CA1288982C - Projector using liquid crystal cells - Google Patents
Projector using liquid crystal cellsInfo
- Publication number
- CA1288982C CA1288982C CA000556105A CA556105A CA1288982C CA 1288982 C CA1288982 C CA 1288982C CA 000556105 A CA000556105 A CA 000556105A CA 556105 A CA556105 A CA 556105A CA 1288982 C CA1288982 C CA 1288982C
- Authority
- CA
- Canada
- Prior art keywords
- liquid crystal
- polarizer
- colored
- crystal cell
- color
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 210000002858 crystal cell Anatomy 0.000 title claims abstract description 78
- 239000004973 liquid crystal related substance Substances 0.000 title claims abstract description 62
- 210000004027 cell Anatomy 0.000 claims abstract description 116
- 230000007935 neutral effect Effects 0.000 claims abstract description 17
- 239000004988 Nematic liquid crystal Substances 0.000 claims abstract description 15
- 239000000203 mixture Substances 0.000 claims abstract description 12
- 239000000654 additive Substances 0.000 claims abstract description 9
- 230000000996 additive effect Effects 0.000 claims abstract description 9
- 239000003086 colorant Substances 0.000 claims description 60
- 230000010287 polarization Effects 0.000 claims description 42
- 230000005284 excitation Effects 0.000 abstract description 14
- 239000007788 liquid Substances 0.000 abstract 1
- 238000010521 absorption reaction Methods 0.000 description 16
- 239000011159 matrix material Substances 0.000 description 11
- 230000005540 biological transmission Effects 0.000 description 9
- 238000010586 diagram Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 230000003252 repetitive effect Effects 0.000 description 3
- 239000007787 solid Substances 0.000 description 2
- 238000010276 construction Methods 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
- G02F1/13471—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells
- G02F1/13473—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells for wavelength filtering or for colour display without the use of colour mosaic filters
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
- G02F1/13475—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which at least one liquid crystal cell or layer is doped with a pleochroic dye, e.g. GH-LC cell
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133528—Polarisers
- G02F1/133533—Colour selective polarisers
Abstract
Abstract:
The present invention relates to a projector having an arrangement of polarizers and liquid crystal cells aligned on an axis of light. The order of the polarizers and cells is a first color polarizer colored in red, a first twisted nematic liquid crystal cell, a second twisted nematic liquid crystal cell, a second color polarizer colored in green, a third twisted nematic liquid, a neutral polarizer and a Guest-Host type colored in blue. Since, according to this, a polarizer having inferior color characteristics can be replaced by a Guest-Host type liquid crystal cell, the excitation purity and the scope of color reproduction are improved. Further, since the mixture of color is additive, the brightness of the reproduced color is also much improved.
The present invention relates to a projector having an arrangement of polarizers and liquid crystal cells aligned on an axis of light. The order of the polarizers and cells is a first color polarizer colored in red, a first twisted nematic liquid crystal cell, a second twisted nematic liquid crystal cell, a second color polarizer colored in green, a third twisted nematic liquid, a neutral polarizer and a Guest-Host type colored in blue. Since, according to this, a polarizer having inferior color characteristics can be replaced by a Guest-Host type liquid crystal cell, the excitation purity and the scope of color reproduction are improved. Further, since the mixture of color is additive, the brightness of the reproduced color is also much improved.
Description
~L281!~
A projector using liquid crystal cells The present invention relates to a projector using liquid crystal cells, and more particularly to a color projector with an arrangement of polarizers and liquid crystal cells which are aligned on an axis of the light to be projected.
A detailed description of the prior art will be found hereinbelow.
An object of the present invention is to provide an economical projector using liquid crystal cells, which is capable of reproducing an image in full color with high color purity and with sufficient brightness and which has a wide scope of color reproduction.
A feature of the present invention is in that, in an arrangement of polarizers and liquid crystal cells of a projector, at least one of the liquid crystal cells is of a Guest-Host type and colored in a color selected from among the three primary colors of an additive mixture, at least one of the polarizers is a color polarizer colored in a color selected from the remaining primary colors, and the total number of Guest~Host cel-ls and color polarizers is three, each of which is colored in a different one of the three primary colors.
According to an embodiment of the present invention, there are used a single Guest-Host type liquid crystal cell, ~Z8E~
which is colored in one of the three primary colors, and two color polarizers, which are colored in the remaining two of the three primary colors, respectively.
In another embodiment of the present invention, there are employed a single polarizer which is colored in one of the three primary colors and two Guest-Host type liquid crystal cells, which are colored in the remaining two of the three primary colors, respectively.
In accordance with an aspect of the invention there is provided a projector having a light source for generating white light for projection; means for collimating the white light generated by said light source; polarizer means, arranged on ah axis of the light, for linearly polarizing the collimated light passing therethrough; liquid crystal cell means arranged with a predetermined positional relationship with said polarizer means on the same axis of light and selectively activated and deactivated in accordance with video signals of an image to be reproduced to control the polarization plane of light passing therethrough; and means for projecting light having passed said polarizer means and said liquid crystal cell means to reproduce an image on a screen in full color, characterized in that at least one of said liquid crystal cell means is a Guest-Host type cell which is colored in a color selected from among three primary colors of an additive mixture and the remaining liquid crystal cell means are non-colored twisted nematic liquid crystal cells;
that at least one of said polarizer means is a color polarizer colored in a color selected from the remaining colors and the remaining polarizers are neutral polarizers;
and that a total number of Guest-Host cells and color polarizers is three, each being colored in a different one of the three primary colors in the additive mixture.
The present invention will be described in detail here-inbelow with the aid of the accompanying drawings, in which:
Figs. la and lb show arrangements of polarizers and liquid crystal cells of prior art projectors;
lXt38982 Fig. 2 schematically shows an overall configuration of a projector in accordance with an embodiment of the present invention;
Fig. 3 is a schematic view showing one example of an arrangement of polarizers and liquid crystal cells in the projector shown in Fig. 2;
Figs.4a to 4e are schematic drawings for explaining the operational principle of color reproduction in the arrange-ment of the example of Fig. 3;
Fig. 5 schematically shows a second example of an arrangement of polarizers and liquid crystal cells in a projector according to the present invention;
Fig. 6 schematically shows a third example of an arrange-ment of polarizers and liquid crystal cells in a projector according to the present invention;
Fig. 7 schematically shows a fourth example of an arrangement of poIarizers and liquid crystal cells in a projector according to the present invention;
Figs. 8a to 8e are schematic drawings for explaining the operational principle of color reproduction in the arrange-ment of the example of Fig. 5;
Figs. 9a to 9d are tables summarizing the relationship between colors to be reproduced and the excitation states of li~uid crystal cells in the arrangements of the examples of Figs. 3, S, 6 and 7;
Fig. 10 is a graphical diagram representing the effect of the present invention in the chromaticity coordinates, in which the scope of the color reproduction in the present invention is compared with that in the prior art of Figs.
la and lb; and Fig. 11 is also a graphical diagram representing the effect of the present invention, in which the brightness of colors reproduced by the present invention are compared with that of the prior art.
Conventionally, a color projector had three black and white cathode-ray tubes (CRTs). Each CRT reproduces an 128~3982 image for one primary color. The images reproduced by the three CRTs are colored by dichroic mirrors in the three primary colors, respectively. Thereafter they are projected on a screen through a projection lens to realize the full-color reproduction of the image. However, in such aconventional apparatus the CRTs did not have sufficient brightness for projection on a large-sized screen and in addition, the size of the apparatus was considerably large, because three CRTs were used. The conventional apparatus was additionally very expensive.
In order to make an apparatus small in size and low in price, various kinds of projectors using liquid crystal cells have been proposed. As shown in Fig. la, for example, a typical embodiment thereof uses a neutral polarizer 2 and three Guest-Host type liquid crystal cells 4, 6 and 8, which are colored in cyan, magenta and yellow, respectively. They are aligned on an axis of the light to be projected. In this example, as is apparent from the selection of color of the cells, the full-color reproduction is realized by a so-called subtractive mixture of color.
However, a colored image reproduced by this apparatus was low in purity of color and does not have sufficient brightness. In addition, the scope of the color reproduction was narrow. These problems result mainly from the fact that the subtractive mixture of color was adopted for reproducing a color image.
Another example of a proposed projector is shown in Fig. lb. This example uses three colored pleochroic polarizers 10, 14 and 18, three twisted nematic liquid crystal cells 12, 16 and 20 and a neutral polarizer 22. The three pleochroic polarizers are colored in red, green and blue which are three primary colors in a so-called additive mixture of color.
According to this example, the brightness of a reproduced image is improved because of the adoption of the additive mixture of color. However, at present, it is very difficult ~2~39~32 to get at a low price, colored pleochroic polarizers for all the three colors which ha~e the necessary color characteristics, such as dichroic ratio, brightness etc.. If polarizers having excellent color characteristics are used for the three colors in order to obtain a reproduction of the image with high color purity and sufficient brightness, the apparatus will be expensive. In addition, although the primary colors of red, green and blue can be easily reproduced, the driving control of the liquid crystal cells becomes somewhat complicated when cyan, magenta and yellow are reproduced.
Referring to Fig. 2, an overall configuration of a projector according to an embodiment of the present invention will be explained.
In the figure, reference numeral 24 denotes a light source. A source such as a xenon lamp, a halogen lamp etc.
is preferable for the light source 24, because, in such light sources, the relative spectral energy distribution has a continuous spectrum in the wavelength region of visible light, which is almost the same as that of solar light. The light source 24 has a reflector 26 for the purpose of effectively using most of the light emitted from the source 24.
The light emitted from the source 24 is converted into a parallel ray of light by a collimating lens 28. The collimated ray of light passes through polarizers and liquid crystal cells arranged according to the present invention.
There are positioned a first polarizer 30 which is a colored pleochroic polarizer ~called a color polarizer, hereinafter).
A first liquid crystal cell 32 which is a twisted nematic liquid crystal cell (abbreviated as a TN cell, hereinafter) is in contact with color polarizer 30.
As is well known, the TN cell 32 has transparent matrix electrodes 34 on both sides thereof, across which an AC
voltage is applied from an electric source 36 under control of a switch 38. Although a single switch is shown in the drawing, the switch 38 consists of unit switches of the number corresponding to the number of elements of the matrix 9~32 electrodes 34. Those unit switches are controlled by a video signal for an image to be reproduced in one of the three primary colors. As a result, portions of the liquid crystal cell, which are put between the corresponding elements of both matrix electrodes 34, are selectively excited. The unit switches are usually formed on the same substrate as the liquid crystal cell and the electrodes.
In contact with the first liquid crystal cell 32, there is provided a second liquid crystal cell 40, which is also a TN cell. The TN cell 40 has transparent electrodes 42 on both sides thereof, across which an AC voltage is applied by an electric source 44 through a switch 46. In the second cell 40, it is sufficient that electrodes 42 be plane electrodes provided over the entire surface of both sides of the cell 40. A second polarizer 48, which is a color polarizer, is positioned adjacent to the cell 40.
There is provided a third liquid crystal cell 50, which is a TN cell. The TN cell 50 is provided with transparent matrix electrodes 52 on both sides thereof, across which an AC voltage is applied by an electric source 54 under control of a switch 56. The matrix electrodes 52 and the switch 56 in this cell 50 are constructed in the same manner as those in the first cell 32. Unit switches of the switch 56 are con-trolled by a video signal for an image to be reproduced in another one of the three primary colors. Next to the third liquid crystal cell S0, there is provided a neutral polarizer 58.
Lastly, there is provided a fourth liquid crystal cell 60, which is a TN cell having the Guest-Host effect, in contact with the polarizer 58. Such a TN cell is abbreviated as a TN/GH cell, hereinafter. The TN/GH cell 60 has transparent matrix electrodes 62 on both sides thereof, across which an AC voltage is applied by an electric source 64 under control of a switch 66. In the fourth cell 60, the matrix electrodes 62 and the switch 66 have the same construction as those in the first cell 32. Unit switches 12~1982 forming the switch 66 are controlled by a video signal for an image to be reproduced in the remaining one of-the three primary colors.
The light which has passed the polarizers and the liquid crystal cells arranged as above is projected by a projection lens 68 to a screen 70, on which a colored and enlarged image is reproduced.
The arrangement of the polarizers and the liquid crystal cells of Fig. 2 will be explained in detail, referring to Fig. 3. In Figure 3, the same reference numerals denote the same parts as in Fig. 2. Parts other than the polarizers and the liquid crystal cells are omitted in the figure in order to facilitate the clear understanding of the arrangement thereof.
As already described, the first polarizer 30 is the color polarizer, which is colored in red. A solid line denoted by R on the polarizer 30 represents an absorption axis and a bro~en line denoted by R,G,B thereon a transmission axis. As is well known, light is linearly polarized when it passes the polariz~r 30. At that time, although light having a polarization plane parallel with the axis R,G,B passes the polarizer 30 with its color unchanged, white light having a polarization plane parallel with the axis R is colored in red when it passes therethrough. Namely, in light having a polarization plane parallel with the axis R, only a red component (component having the wavelength corresponding to red) can pass the polarizer 30 and other components, i.e., green and blue, are blocked.
The irst liquid crystal cell 32 is the TN cell, and therefore, when no AC voltage is applied across the electrodes 34, light passing therethrough is subject to a rotary polarization of 90. Incidentally, when no voltage is applied across the electrodes of a cell, it will be understood here-inafter that the cell is in the OFF state or that the excitation state of the cell is OFF. To the contrary, when an AC voltage is applied across the electrodes 34, i.e. the 128~39~
cell 32 is in the ON state, light passes the cell 32 without being subject to any rotary polarization. Since the second cell 40 is also the TN cell, the same applies thereto.
The second polarizer 48 is a color polarizer colored in green and the direction of an absorption axis G coincides with that of the absorption axis R of the first polarizer 30. There-fore, white light having a polarization plane parallel with the axis G is colored in green, when it passes the polarizer 48.
The third polarizer 58 is the neutral polarizer, the absorption axis of which is at a right angle with respect to the absorption axes R and E of the polarizers 30 and 48.
The TN/GH cell 60 is colored in blue. Therefore, when the TN/GH cell 60 is in the OFF state, light passing there-through is subject to a rotary polarization of 90 and is colored in blue. To the contrary, when the TN~GH cell 60 is in the ON state, light passes therethrough without any rotary polarization, so that the color of the light is not changed.
In the arrangement described above, the fourth cell 60, which is the TN/GH cell, was colored in blue. However, the color of the TN/GH cell 60 is not limited to blue, but can be freely selected from among the three primary colors. At that time, the colors of the two color polarizers 30 and 48 must be selected accordingly. If, for example, green is selected as a color of the TN/GH cell 60, red and blue are assigned to the respective color polarizers 30 and 48. For the arrangement as shown in Fig. 3, a total of six combinations of colors for the color polarizers 30 and 48 and the TN/GH cell 60 can be considered.
Referring to Figs. 4a to 4e, the operational principle of the color reproduction in the arrangement of Fig. 3 will be explained. In the figures, the same reference numerals denote the same parts as in Fig. 3.
Fig. 4a is a drawing for explaining the reproduction of red. Natural light, which is collimated by the lens 28, is applied to the aforesaid arrangement of polarizers and liquid crystal cells from the left in the figure. When the light is ~2~9~2 app~ied to polarizer 30, it is linearly polarized so that two kinds of components thereof pass through; one is red light, as denoted by R, having a polarization plane parallel with the absorption axis and the o~her is white light, as denoted by S W, having a polarization plane parallel with the transmission axis.
Here, it is to be noted that arrows are attached to both the light having passed the polarizer 30 only for the purpose of facilitating the understanding of the effect of the rotary polarization in the liquid crystal cells. The same is applied to the following explanation.
The first cell 32 is maintained in an ON state, and therefore the rotary polarization does not occur in this cell.
This state is represented by solid and broken lines indicated in parallel on both sides of the cell 32. The light from the polarizer 30 passes the cell 32 without any change.
The second cell 40 is kept in the OFF state. Therefore, rotary polarization takes place on the light passing there-through. This state is represented by solid and broken lines at right angles on both sides of the cell 40. The light from the cell 32 is subject to a rotary polarization of 90 in cell 40. This effect will be easily understood from the condition of the arrows attached to the light having passed through the cell 40.
White light from the cell 40 is colored green by the polarizer 48, because its polarization plane is in parallel with the absorption axis of the polarizer 48. Red light passes the polarizer 48 as it is, because its polarization plane is in parallel with the transmission axis of the polarizer 48.
Therefore, the light having passed through the polarizer 48 contains green and red components, as shown in the figure.
The TN cell 50 is in the OFF state, and therefore the light from the polarizer 48 is subject to a rotary polarization of 90 so that the polarization plane of a green component of the light from the cell 50 becomes parallel with the ~2~9~Z
absorption axis of the polarizer 58. As a result, the green component is blocked by the polarizer 58, and only the red component passes therethrough.
Since the TN/GH cell 60, which is colored in blue, is in the ON state, the light from the polarizer 58 is not subject to any rotary polarization in the cell 60 and there-fore passes therethrough without any change in color. As a result, when the light having passed the TN/GH cell 60 is projected on the screen 70, an image colored in red is reproduced thereon.
Referring next to Fig. 4b, the operational principle of the reproduction of a green image will be explained. In this case, as apparent from the figure, the polarization condition of the light having passed the second polarizer 48 is the same as that in the case of Fig. 4a. This results from the fact that, although there is a difference in the order of excitation of the first and second cells 32 and 40 between Figs. 4a and 4b, nevertheless the polarization plane of the polarized light is rotated only once.
Being different from the case of Fig. 4a, the third cell 50 is in the ON state. Therefore, the light from the polarizer 48 passes the cell 50 without any rotary polarization. Of the two components of the light having passed the cell 50, the red component is blocked by the polarizer 58, because its polarization plane is parallel with the absorption axis of the polarizer 58. Only the green component, the polarization plane of which is parallel with the transmission axis of the polarizer 58, passes therethrough.
Similar to the case of Fig. 4a, since the TN/G~ cell 60 is in the ON state, the light from the polarizer 58 passes the cell 60 without any rotary polarization and hence with no change in the color. As a result, when the light having passed the cell 60 is projected by the projection lens 68, an image colored in green is reproduced on the screen 70.
In Fig. qc, there is shown the operational principle of the reproduction of an image based on blue light. It will be ~X~1~9~2 understood from the foregoing explanation that the polarization condition of light from the cell 40 is shifted by 90 from that in Fig. 4b or 4a, because the light from the polarizer 30 is rotated twice by 90. As a result, the red component in the light from the cell 40 is blocked by the polarizer 48, because its polarization plane is parallel with the absorption axis thereof, and only the white component passes the polarizer 48, because its polarization plane is parallel with the transmission axis thereof.
The light having passed the polarizer 48, which contains only the white component, is subject to a rotary polarization of 90 in the cell 50, which is in the OFF state. The polarization plane of light having passed the cell 50 becomes parallel with the transmission axis of the neutral polarizer lS 58, so that the light passes therethrough.
Since the TN/GH cell 60 is in the OFF state, white light passing therethrough is rotated by 90 and colored in blue.
Therefore, if the light having passed the cell 60 is projected by the projection lens 68, an image colored in blue is reproduced on the screen 70.
In Figs. 4d and 4e, the reproduction of white and black is shown~ However, the detailed explanation thereof is omitted to avoid a redundant explanation. The operational principle thereof will be followed by referring to the fcre-going explanation In order to realize the reproduction of an image in fullcolor, it is necessary to be capable of reproducing not only the primary colors in the additive mixture, i.e., red (R), green (G) and blue (B?, but also those in the subtractive mixture, i.e., cyan (C?, magenta (M) and yellow (Y)~
Here it is to be noted that the following relations exist in the six colors mentioned above G + B = W - R = C
B + R = W - G = M
R + G = W - s = Y
1;~l38982 Therefore, cyan, magenta and yellow can be reproduced by using the operational principles for reproducing red, green and ~lue, in view of the aforesaid relationship.
For the purpose of reproducing of yellow, for example, the operations for reproducing red and green are combined.
Namely, if the excitation state of the cells as shown in Fig. 4a and that as shown in Fig. 4b are repeated at pre-determined frequencies, an image colored in red and an image colored in green are reproduced on the screen 70 alternately.
From Figs. 4a and 4b, it will be understood that there is a difference in the excitation condition of the cells 32, 40 and 50. In this repetitive operation, therefore, only the cells 32, 40 and 50 are controlled intermittently and the cell 60 is maintained at the ON state, during the reproduction of yellow.
If the frequency of the repetitive operation is selected to be more than 30 Hz, the human eye cannot see both images in distinction from each other, but only recognize a single yellow-colored image. Further, if the ratio of the duration of the state of Fig. 4a or 4b to the repetition period is changed, reddish or greenish yellow can be reproduced.
Similarly, on the basis of the above mentioned relation-ship, if the excitation states of Figs. 4a and 4c are repeated at a frequency of more than 30 Hz, an image colored in magenta can be reproduced. If the ratio of the duration of the state of Fig. 4a or 4c to the repetition period is changed, the reproduction of redd.ish or bluish magenta can be realized. Further, if the excitation states of Figs. 4b and 4c are repeated, the reproduction of an image colored in cyan can be realized. Also in this case, if the ratio of the duration of the state of Fig. 4b or 4c to the repetition period is changed, it is possible to reproduce greenish or bluish cyan.
In this manner, a full-color image can bP reproduced by the arrangement of Fig. 3. The excitation state of the liquid crystal cells 32, 40, 50 and 60 in this embodiment ~Z8~
is summarized in a table shown in Fig. 9a. In the table, the indications "ON/OFF" and "OFF/ON" mean that cells with these indications are subject to the repetitive operation of the intermittent excitation as described above.
Some modifications of the combination of the polarizers and the liquid crystal cells will be explained, referring to Figs. 5, 6 and 7.
Referring first to Fig. 5, there is shown an example of an arrangement of polarizers and liquid crystal cells, in which two color polarizers 62, 66, two TN cells 64, 68, a neu-tral polarizer 70 and a TN/GH cell 72 are used. In this arrangement, there is one less TN cell than in the arrangement shown in Fig. 3.
In Fig. 3, the TN cell 40 has no matrix electrodes and is used only for rotating the polarization plane of light passing therethrough. The red image, for example, is already produced by the cooperation of the polarizer 30 and the selective excitation of the matrix electrodes of the cell 32.
In Fig. 5, the function done by the two TN cells 32 and 40 in Fig. 3 is achieved by the single TN cell 64. Therefore, the cell 64 must be provided with the matrix electrodes on both sides.
Similarly to the case of Fig. 3, the first polarizer 62 is colored in red and the second polarizer 66 in green.
However, the absorption axis of the second polarizer 66 is at right angles to that of the first polarizer 62. This difference in the direction of the absorption axis is because the TN cell 40 has been omitted. The TN/GH cell 72 is colored in blue.
Further, the color of the TN/GH cell 72 is not limited to blue, but can be freely selected from among the three primary colors. The color of the polarizers must be selected in view of the color selected for the TN/GH cell. If green is determined for the TN/GH cell, the colors of the two color polarizers must be selected from red and blue, respectively.
Therefore, six combinations for the selection of colors for ~2~3~9~32 the polarizers and a TN/GH cell are considered.
The operational principles of reproduction of red, green, blue, white and black are shown in Figs. 8a to 8e in a similar manner to Figs. 4a to 4e. In the following, however, S only the reproduction of red will be explained, referring to Fig. 8a, because of the similarity of the operation and hence the avoidance of a redundant explanation.
In Fig. 8a, when a natural light passes the polarizer 62, the light is converted into a light composed of a red component having a polarization plane parallel with the absorption axis of the polarizer 62 and a white component having a polarization plane parallel with the transmission axis thereof. Since the TN cèll 64 is in the ON state, the light from the polarizer 62 passes the cell 64 without any rotary polarization.
The light from the TN cell 64 passes the polarizer 66.
At that time, the white component from the TN cell 64 is colored green, because the polarization plane of the white component is parallel with the absorption axis of the polarizer 66 which is colored green. The red component, the polarization plane of which is parallel with the transmission axis, passes the polarizer 66 without any change in color.
The TN cell 68 is maintained in the ON state, and there-fore the light from the polarizer 66 passes therethrough without any rotary polarization. Although the light having passed the TN cell 68 has two components of red and green, since the polarization plane of the green component is parallel with the absorption axis of the neutral polarizer 70, it is blocked and only the red component, the polarization plane of which is parallel with the transmission axis, passes the polarizer 70.
The TN/GH cell 72 is in the ON state, and therefore the light from the polarizer 70 passes the cell 72 without any rotary polarization and hence without any change in color.
When the light having passed the TN/GH cell 72 is projected by the pro~ection lens 68, an image colored in red is reproduced on the screen 70.
In an analogous way, green and blue can be reproduced as is shown in Figs. 8b and 8c, and also white and black can be reproduced as is shown in Figs. 8d and 8e. The excitation condition of the cells in the reproduction of these colors are summarized in a table shown in Fig. 9b. Also in this case, as will be understood from the table, yellow, magenta and cyan can be reproduced by repeatedly switching between two states selected from among the states of Figs. 8a to 8c.
In Fig. 6 there is shown another example of an arrange-ment of polarizers and liquid crystal cells, in which a neutral polarizer 74, a TN/GH cell 76, two TN cells 78, 82 and two color polarizers 80, 84 are employed. Also in this example, all the cells must be provided with matrix electrodes on both sides Df their respective cells in a similar manner to the case of Fig. 5. The TN/GH cell 76 is colored in blue, and the two color polarizers 80 and 84 are colored in red and green, respectively. Further, the absorption axes of the two color polarizers 80 and 84 are at right angles to 2Q each other.
Similarly to the foregoing examples, the color of the TN/GH cell is not limited to blue, but can be freely selected from among the three primary colors. The colors of the two color polarizers must be selected, taking into account the color selected for the TN/GH cell. I~ green is determined for the TN~GH cell, the colors of the polarizers must be selected from red and blue, respectively. There are six combinations f~r the selection of colors for the polarizers and the TN/GH cell.
The excitation condition of the cells of this example is summarized in a table shown in Fig. 9c. Although the operational principle of this example is not shown, it will be understood from the table of Fig. 9c and the analogy of the foregoing description that all the six colors and white and black can be reproduced.
9~2 Still another example of an arrangement of polarizers and liquid crystal cells is shown in Fig~ 7. In this example, there are employed a single color polarizer 86, two TN cells ~8, 96, two neutral polarizers 90, 98 and two TN/GH cells 92, 94. A feature of this example which is different from the foregoing examples is in the use of the two TN/GH cells 92 and 94. The single color polarizer 86 is colored in red and the TN/GH cells 92 and 94 are colored in green and blue, respectively.
Also in this case, the color of the TN/GH cells are not limited to green and blue, but can be freely selected from among the three primary colors. The color of the color polarizer must be selected in view of the colors selected for the TN/GH cells.
The excitation condition of the cells in this example is summarized in a table shown in Fig. 9d. Also with respect to this example, although the operational principle is not shown, it will be understood from the table of Fig. 9d and the foregoing description that eight colors, i.e., red, green, blue, yellow, magenta, and cyan including white and black, can be reproduced.
The effect of the present invention ~ill be discussed, compared with the prior art. The arrangement of the polarizers and the liquid crystal cells shown in Fig. 3 is taken as an example of the present invention, and both the arrangements of E'igs. la and lb are taken as examples of the prior art.
Fig. 10 is a known chromaticity diagram, in which coordinates of red, green and blue reproduced by the above mentioned three examples are indicated. The rightmost correspond to the coordinates of red and the leftmost to those of blue. The coordinates lying therebetween are of green. The area of triangles formed by these coordinates represent the scope of color which can be reproduced by the respective examples. As is apparent from the diagram, the scope of the color reproduction of the present invention is considerably improved, compared with that of the prior art ~2~3898Z
of Fig. la (cf. triangles of a solid line and a chain line in Fig. 10).
In this diagram, coordinates of red, green and blue reproduced by a color CRT in accordance with color signals in the NTSC system are indicated by black dots R, G and ~, respectively. It is to be noted that they do not indicate the coordinate of respective colors which are reproduced by a projector using CRTs. The scope of colors capable of actually being reproduced by a CRT type projector becomes smaller than that indicated by the black dots R, G and B, because it greatly depends on the characteristics and capabilities of dichroic mirrors used in the projector. From this diagram, it will be understood that the present invention reproduces colors which are closer to those reproduced by the color CRT, compared with two other examples. Further, a mark x indicates coordinates of a standard C source.
Referring next to Fig. 11, the comparison of the bright-ness of reproduced colors will be discussed. In the figure, the ordinate represents luminance of respective colors reproduced by the above mentioned three examples in term of the ratio when the value of the present invention is made 1Ø
The abscissa thereof represents a dominant wavelength ~d f the respective colors. Marks indicative of respective values are the same as ones in Fig. 10. For the comparison, values of the dominant wavelength of respective colors reproduced by a color CRT are indicated on the abscissa.
As is apparent from the figure, with respect to blue, for example, the present invention is about 20% brighter than the prior art of Fig. la and about 50~ brighter than that of Fig. lb. With respect to green, the present invention is about 50% brighter than the prior art of Fig. la and about 10% brighter than that of Fig. lb. Further, with respect to red, the present invention is over 30% brighter than the prior art of Fig. la and about 10% brighter than that of Fig. lb. In this manner, as a whole, the present invention is 10% to 5Q~ superior in the brightness of the reproduced colors over the prior art.
A projector using liquid crystal cells The present invention relates to a projector using liquid crystal cells, and more particularly to a color projector with an arrangement of polarizers and liquid crystal cells which are aligned on an axis of the light to be projected.
A detailed description of the prior art will be found hereinbelow.
An object of the present invention is to provide an economical projector using liquid crystal cells, which is capable of reproducing an image in full color with high color purity and with sufficient brightness and which has a wide scope of color reproduction.
A feature of the present invention is in that, in an arrangement of polarizers and liquid crystal cells of a projector, at least one of the liquid crystal cells is of a Guest-Host type and colored in a color selected from among the three primary colors of an additive mixture, at least one of the polarizers is a color polarizer colored in a color selected from the remaining primary colors, and the total number of Guest~Host cel-ls and color polarizers is three, each of which is colored in a different one of the three primary colors.
According to an embodiment of the present invention, there are used a single Guest-Host type liquid crystal cell, ~Z8E~
which is colored in one of the three primary colors, and two color polarizers, which are colored in the remaining two of the three primary colors, respectively.
In another embodiment of the present invention, there are employed a single polarizer which is colored in one of the three primary colors and two Guest-Host type liquid crystal cells, which are colored in the remaining two of the three primary colors, respectively.
In accordance with an aspect of the invention there is provided a projector having a light source for generating white light for projection; means for collimating the white light generated by said light source; polarizer means, arranged on ah axis of the light, for linearly polarizing the collimated light passing therethrough; liquid crystal cell means arranged with a predetermined positional relationship with said polarizer means on the same axis of light and selectively activated and deactivated in accordance with video signals of an image to be reproduced to control the polarization plane of light passing therethrough; and means for projecting light having passed said polarizer means and said liquid crystal cell means to reproduce an image on a screen in full color, characterized in that at least one of said liquid crystal cell means is a Guest-Host type cell which is colored in a color selected from among three primary colors of an additive mixture and the remaining liquid crystal cell means are non-colored twisted nematic liquid crystal cells;
that at least one of said polarizer means is a color polarizer colored in a color selected from the remaining colors and the remaining polarizers are neutral polarizers;
and that a total number of Guest-Host cells and color polarizers is three, each being colored in a different one of the three primary colors in the additive mixture.
The present invention will be described in detail here-inbelow with the aid of the accompanying drawings, in which:
Figs. la and lb show arrangements of polarizers and liquid crystal cells of prior art projectors;
lXt38982 Fig. 2 schematically shows an overall configuration of a projector in accordance with an embodiment of the present invention;
Fig. 3 is a schematic view showing one example of an arrangement of polarizers and liquid crystal cells in the projector shown in Fig. 2;
Figs.4a to 4e are schematic drawings for explaining the operational principle of color reproduction in the arrange-ment of the example of Fig. 3;
Fig. 5 schematically shows a second example of an arrangement of polarizers and liquid crystal cells in a projector according to the present invention;
Fig. 6 schematically shows a third example of an arrange-ment of polarizers and liquid crystal cells in a projector according to the present invention;
Fig. 7 schematically shows a fourth example of an arrangement of poIarizers and liquid crystal cells in a projector according to the present invention;
Figs. 8a to 8e are schematic drawings for explaining the operational principle of color reproduction in the arrange-ment of the example of Fig. 5;
Figs. 9a to 9d are tables summarizing the relationship between colors to be reproduced and the excitation states of li~uid crystal cells in the arrangements of the examples of Figs. 3, S, 6 and 7;
Fig. 10 is a graphical diagram representing the effect of the present invention in the chromaticity coordinates, in which the scope of the color reproduction in the present invention is compared with that in the prior art of Figs.
la and lb; and Fig. 11 is also a graphical diagram representing the effect of the present invention, in which the brightness of colors reproduced by the present invention are compared with that of the prior art.
Conventionally, a color projector had three black and white cathode-ray tubes (CRTs). Each CRT reproduces an 128~3982 image for one primary color. The images reproduced by the three CRTs are colored by dichroic mirrors in the three primary colors, respectively. Thereafter they are projected on a screen through a projection lens to realize the full-color reproduction of the image. However, in such aconventional apparatus the CRTs did not have sufficient brightness for projection on a large-sized screen and in addition, the size of the apparatus was considerably large, because three CRTs were used. The conventional apparatus was additionally very expensive.
In order to make an apparatus small in size and low in price, various kinds of projectors using liquid crystal cells have been proposed. As shown in Fig. la, for example, a typical embodiment thereof uses a neutral polarizer 2 and three Guest-Host type liquid crystal cells 4, 6 and 8, which are colored in cyan, magenta and yellow, respectively. They are aligned on an axis of the light to be projected. In this example, as is apparent from the selection of color of the cells, the full-color reproduction is realized by a so-called subtractive mixture of color.
However, a colored image reproduced by this apparatus was low in purity of color and does not have sufficient brightness. In addition, the scope of the color reproduction was narrow. These problems result mainly from the fact that the subtractive mixture of color was adopted for reproducing a color image.
Another example of a proposed projector is shown in Fig. lb. This example uses three colored pleochroic polarizers 10, 14 and 18, three twisted nematic liquid crystal cells 12, 16 and 20 and a neutral polarizer 22. The three pleochroic polarizers are colored in red, green and blue which are three primary colors in a so-called additive mixture of color.
According to this example, the brightness of a reproduced image is improved because of the adoption of the additive mixture of color. However, at present, it is very difficult ~2~39~32 to get at a low price, colored pleochroic polarizers for all the three colors which ha~e the necessary color characteristics, such as dichroic ratio, brightness etc.. If polarizers having excellent color characteristics are used for the three colors in order to obtain a reproduction of the image with high color purity and sufficient brightness, the apparatus will be expensive. In addition, although the primary colors of red, green and blue can be easily reproduced, the driving control of the liquid crystal cells becomes somewhat complicated when cyan, magenta and yellow are reproduced.
Referring to Fig. 2, an overall configuration of a projector according to an embodiment of the present invention will be explained.
In the figure, reference numeral 24 denotes a light source. A source such as a xenon lamp, a halogen lamp etc.
is preferable for the light source 24, because, in such light sources, the relative spectral energy distribution has a continuous spectrum in the wavelength region of visible light, which is almost the same as that of solar light. The light source 24 has a reflector 26 for the purpose of effectively using most of the light emitted from the source 24.
The light emitted from the source 24 is converted into a parallel ray of light by a collimating lens 28. The collimated ray of light passes through polarizers and liquid crystal cells arranged according to the present invention.
There are positioned a first polarizer 30 which is a colored pleochroic polarizer ~called a color polarizer, hereinafter).
A first liquid crystal cell 32 which is a twisted nematic liquid crystal cell (abbreviated as a TN cell, hereinafter) is in contact with color polarizer 30.
As is well known, the TN cell 32 has transparent matrix electrodes 34 on both sides thereof, across which an AC
voltage is applied from an electric source 36 under control of a switch 38. Although a single switch is shown in the drawing, the switch 38 consists of unit switches of the number corresponding to the number of elements of the matrix 9~32 electrodes 34. Those unit switches are controlled by a video signal for an image to be reproduced in one of the three primary colors. As a result, portions of the liquid crystal cell, which are put between the corresponding elements of both matrix electrodes 34, are selectively excited. The unit switches are usually formed on the same substrate as the liquid crystal cell and the electrodes.
In contact with the first liquid crystal cell 32, there is provided a second liquid crystal cell 40, which is also a TN cell. The TN cell 40 has transparent electrodes 42 on both sides thereof, across which an AC voltage is applied by an electric source 44 through a switch 46. In the second cell 40, it is sufficient that electrodes 42 be plane electrodes provided over the entire surface of both sides of the cell 40. A second polarizer 48, which is a color polarizer, is positioned adjacent to the cell 40.
There is provided a third liquid crystal cell 50, which is a TN cell. The TN cell 50 is provided with transparent matrix electrodes 52 on both sides thereof, across which an AC voltage is applied by an electric source 54 under control of a switch 56. The matrix electrodes 52 and the switch 56 in this cell 50 are constructed in the same manner as those in the first cell 32. Unit switches of the switch 56 are con-trolled by a video signal for an image to be reproduced in another one of the three primary colors. Next to the third liquid crystal cell S0, there is provided a neutral polarizer 58.
Lastly, there is provided a fourth liquid crystal cell 60, which is a TN cell having the Guest-Host effect, in contact with the polarizer 58. Such a TN cell is abbreviated as a TN/GH cell, hereinafter. The TN/GH cell 60 has transparent matrix electrodes 62 on both sides thereof, across which an AC voltage is applied by an electric source 64 under control of a switch 66. In the fourth cell 60, the matrix electrodes 62 and the switch 66 have the same construction as those in the first cell 32. Unit switches 12~1982 forming the switch 66 are controlled by a video signal for an image to be reproduced in the remaining one of-the three primary colors.
The light which has passed the polarizers and the liquid crystal cells arranged as above is projected by a projection lens 68 to a screen 70, on which a colored and enlarged image is reproduced.
The arrangement of the polarizers and the liquid crystal cells of Fig. 2 will be explained in detail, referring to Fig. 3. In Figure 3, the same reference numerals denote the same parts as in Fig. 2. Parts other than the polarizers and the liquid crystal cells are omitted in the figure in order to facilitate the clear understanding of the arrangement thereof.
As already described, the first polarizer 30 is the color polarizer, which is colored in red. A solid line denoted by R on the polarizer 30 represents an absorption axis and a bro~en line denoted by R,G,B thereon a transmission axis. As is well known, light is linearly polarized when it passes the polariz~r 30. At that time, although light having a polarization plane parallel with the axis R,G,B passes the polarizer 30 with its color unchanged, white light having a polarization plane parallel with the axis R is colored in red when it passes therethrough. Namely, in light having a polarization plane parallel with the axis R, only a red component (component having the wavelength corresponding to red) can pass the polarizer 30 and other components, i.e., green and blue, are blocked.
The irst liquid crystal cell 32 is the TN cell, and therefore, when no AC voltage is applied across the electrodes 34, light passing therethrough is subject to a rotary polarization of 90. Incidentally, when no voltage is applied across the electrodes of a cell, it will be understood here-inafter that the cell is in the OFF state or that the excitation state of the cell is OFF. To the contrary, when an AC voltage is applied across the electrodes 34, i.e. the 128~39~
cell 32 is in the ON state, light passes the cell 32 without being subject to any rotary polarization. Since the second cell 40 is also the TN cell, the same applies thereto.
The second polarizer 48 is a color polarizer colored in green and the direction of an absorption axis G coincides with that of the absorption axis R of the first polarizer 30. There-fore, white light having a polarization plane parallel with the axis G is colored in green, when it passes the polarizer 48.
The third polarizer 58 is the neutral polarizer, the absorption axis of which is at a right angle with respect to the absorption axes R and E of the polarizers 30 and 48.
The TN/GH cell 60 is colored in blue. Therefore, when the TN/GH cell 60 is in the OFF state, light passing there-through is subject to a rotary polarization of 90 and is colored in blue. To the contrary, when the TN~GH cell 60 is in the ON state, light passes therethrough without any rotary polarization, so that the color of the light is not changed.
In the arrangement described above, the fourth cell 60, which is the TN/GH cell, was colored in blue. However, the color of the TN/GH cell 60 is not limited to blue, but can be freely selected from among the three primary colors. At that time, the colors of the two color polarizers 30 and 48 must be selected accordingly. If, for example, green is selected as a color of the TN/GH cell 60, red and blue are assigned to the respective color polarizers 30 and 48. For the arrangement as shown in Fig. 3, a total of six combinations of colors for the color polarizers 30 and 48 and the TN/GH cell 60 can be considered.
Referring to Figs. 4a to 4e, the operational principle of the color reproduction in the arrangement of Fig. 3 will be explained. In the figures, the same reference numerals denote the same parts as in Fig. 3.
Fig. 4a is a drawing for explaining the reproduction of red. Natural light, which is collimated by the lens 28, is applied to the aforesaid arrangement of polarizers and liquid crystal cells from the left in the figure. When the light is ~2~9~2 app~ied to polarizer 30, it is linearly polarized so that two kinds of components thereof pass through; one is red light, as denoted by R, having a polarization plane parallel with the absorption axis and the o~her is white light, as denoted by S W, having a polarization plane parallel with the transmission axis.
Here, it is to be noted that arrows are attached to both the light having passed the polarizer 30 only for the purpose of facilitating the understanding of the effect of the rotary polarization in the liquid crystal cells. The same is applied to the following explanation.
The first cell 32 is maintained in an ON state, and therefore the rotary polarization does not occur in this cell.
This state is represented by solid and broken lines indicated in parallel on both sides of the cell 32. The light from the polarizer 30 passes the cell 32 without any change.
The second cell 40 is kept in the OFF state. Therefore, rotary polarization takes place on the light passing there-through. This state is represented by solid and broken lines at right angles on both sides of the cell 40. The light from the cell 32 is subject to a rotary polarization of 90 in cell 40. This effect will be easily understood from the condition of the arrows attached to the light having passed through the cell 40.
White light from the cell 40 is colored green by the polarizer 48, because its polarization plane is in parallel with the absorption axis of the polarizer 48. Red light passes the polarizer 48 as it is, because its polarization plane is in parallel with the transmission axis of the polarizer 48.
Therefore, the light having passed through the polarizer 48 contains green and red components, as shown in the figure.
The TN cell 50 is in the OFF state, and therefore the light from the polarizer 48 is subject to a rotary polarization of 90 so that the polarization plane of a green component of the light from the cell 50 becomes parallel with the ~2~9~Z
absorption axis of the polarizer 58. As a result, the green component is blocked by the polarizer 58, and only the red component passes therethrough.
Since the TN/GH cell 60, which is colored in blue, is in the ON state, the light from the polarizer 58 is not subject to any rotary polarization in the cell 60 and there-fore passes therethrough without any change in color. As a result, when the light having passed the TN/GH cell 60 is projected on the screen 70, an image colored in red is reproduced thereon.
Referring next to Fig. 4b, the operational principle of the reproduction of a green image will be explained. In this case, as apparent from the figure, the polarization condition of the light having passed the second polarizer 48 is the same as that in the case of Fig. 4a. This results from the fact that, although there is a difference in the order of excitation of the first and second cells 32 and 40 between Figs. 4a and 4b, nevertheless the polarization plane of the polarized light is rotated only once.
Being different from the case of Fig. 4a, the third cell 50 is in the ON state. Therefore, the light from the polarizer 48 passes the cell 50 without any rotary polarization. Of the two components of the light having passed the cell 50, the red component is blocked by the polarizer 58, because its polarization plane is parallel with the absorption axis of the polarizer 58. Only the green component, the polarization plane of which is parallel with the transmission axis of the polarizer 58, passes therethrough.
Similar to the case of Fig. 4a, since the TN/G~ cell 60 is in the ON state, the light from the polarizer 58 passes the cell 60 without any rotary polarization and hence with no change in the color. As a result, when the light having passed the cell 60 is projected by the projection lens 68, an image colored in green is reproduced on the screen 70.
In Fig. qc, there is shown the operational principle of the reproduction of an image based on blue light. It will be ~X~1~9~2 understood from the foregoing explanation that the polarization condition of light from the cell 40 is shifted by 90 from that in Fig. 4b or 4a, because the light from the polarizer 30 is rotated twice by 90. As a result, the red component in the light from the cell 40 is blocked by the polarizer 48, because its polarization plane is parallel with the absorption axis thereof, and only the white component passes the polarizer 48, because its polarization plane is parallel with the transmission axis thereof.
The light having passed the polarizer 48, which contains only the white component, is subject to a rotary polarization of 90 in the cell 50, which is in the OFF state. The polarization plane of light having passed the cell 50 becomes parallel with the transmission axis of the neutral polarizer lS 58, so that the light passes therethrough.
Since the TN/GH cell 60 is in the OFF state, white light passing therethrough is rotated by 90 and colored in blue.
Therefore, if the light having passed the cell 60 is projected by the projection lens 68, an image colored in blue is reproduced on the screen 70.
In Figs. 4d and 4e, the reproduction of white and black is shown~ However, the detailed explanation thereof is omitted to avoid a redundant explanation. The operational principle thereof will be followed by referring to the fcre-going explanation In order to realize the reproduction of an image in fullcolor, it is necessary to be capable of reproducing not only the primary colors in the additive mixture, i.e., red (R), green (G) and blue (B?, but also those in the subtractive mixture, i.e., cyan (C?, magenta (M) and yellow (Y)~
Here it is to be noted that the following relations exist in the six colors mentioned above G + B = W - R = C
B + R = W - G = M
R + G = W - s = Y
1;~l38982 Therefore, cyan, magenta and yellow can be reproduced by using the operational principles for reproducing red, green and ~lue, in view of the aforesaid relationship.
For the purpose of reproducing of yellow, for example, the operations for reproducing red and green are combined.
Namely, if the excitation state of the cells as shown in Fig. 4a and that as shown in Fig. 4b are repeated at pre-determined frequencies, an image colored in red and an image colored in green are reproduced on the screen 70 alternately.
From Figs. 4a and 4b, it will be understood that there is a difference in the excitation condition of the cells 32, 40 and 50. In this repetitive operation, therefore, only the cells 32, 40 and 50 are controlled intermittently and the cell 60 is maintained at the ON state, during the reproduction of yellow.
If the frequency of the repetitive operation is selected to be more than 30 Hz, the human eye cannot see both images in distinction from each other, but only recognize a single yellow-colored image. Further, if the ratio of the duration of the state of Fig. 4a or 4b to the repetition period is changed, reddish or greenish yellow can be reproduced.
Similarly, on the basis of the above mentioned relation-ship, if the excitation states of Figs. 4a and 4c are repeated at a frequency of more than 30 Hz, an image colored in magenta can be reproduced. If the ratio of the duration of the state of Fig. 4a or 4c to the repetition period is changed, the reproduction of redd.ish or bluish magenta can be realized. Further, if the excitation states of Figs. 4b and 4c are repeated, the reproduction of an image colored in cyan can be realized. Also in this case, if the ratio of the duration of the state of Fig. 4b or 4c to the repetition period is changed, it is possible to reproduce greenish or bluish cyan.
In this manner, a full-color image can bP reproduced by the arrangement of Fig. 3. The excitation state of the liquid crystal cells 32, 40, 50 and 60 in this embodiment ~Z8~
is summarized in a table shown in Fig. 9a. In the table, the indications "ON/OFF" and "OFF/ON" mean that cells with these indications are subject to the repetitive operation of the intermittent excitation as described above.
Some modifications of the combination of the polarizers and the liquid crystal cells will be explained, referring to Figs. 5, 6 and 7.
Referring first to Fig. 5, there is shown an example of an arrangement of polarizers and liquid crystal cells, in which two color polarizers 62, 66, two TN cells 64, 68, a neu-tral polarizer 70 and a TN/GH cell 72 are used. In this arrangement, there is one less TN cell than in the arrangement shown in Fig. 3.
In Fig. 3, the TN cell 40 has no matrix electrodes and is used only for rotating the polarization plane of light passing therethrough. The red image, for example, is already produced by the cooperation of the polarizer 30 and the selective excitation of the matrix electrodes of the cell 32.
In Fig. 5, the function done by the two TN cells 32 and 40 in Fig. 3 is achieved by the single TN cell 64. Therefore, the cell 64 must be provided with the matrix electrodes on both sides.
Similarly to the case of Fig. 3, the first polarizer 62 is colored in red and the second polarizer 66 in green.
However, the absorption axis of the second polarizer 66 is at right angles to that of the first polarizer 62. This difference in the direction of the absorption axis is because the TN cell 40 has been omitted. The TN/GH cell 72 is colored in blue.
Further, the color of the TN/GH cell 72 is not limited to blue, but can be freely selected from among the three primary colors. The color of the polarizers must be selected in view of the color selected for the TN/GH cell. If green is determined for the TN/GH cell, the colors of the two color polarizers must be selected from red and blue, respectively.
Therefore, six combinations for the selection of colors for ~2~3~9~32 the polarizers and a TN/GH cell are considered.
The operational principles of reproduction of red, green, blue, white and black are shown in Figs. 8a to 8e in a similar manner to Figs. 4a to 4e. In the following, however, S only the reproduction of red will be explained, referring to Fig. 8a, because of the similarity of the operation and hence the avoidance of a redundant explanation.
In Fig. 8a, when a natural light passes the polarizer 62, the light is converted into a light composed of a red component having a polarization plane parallel with the absorption axis of the polarizer 62 and a white component having a polarization plane parallel with the transmission axis thereof. Since the TN cèll 64 is in the ON state, the light from the polarizer 62 passes the cell 64 without any rotary polarization.
The light from the TN cell 64 passes the polarizer 66.
At that time, the white component from the TN cell 64 is colored green, because the polarization plane of the white component is parallel with the absorption axis of the polarizer 66 which is colored green. The red component, the polarization plane of which is parallel with the transmission axis, passes the polarizer 66 without any change in color.
The TN cell 68 is maintained in the ON state, and there-fore the light from the polarizer 66 passes therethrough without any rotary polarization. Although the light having passed the TN cell 68 has two components of red and green, since the polarization plane of the green component is parallel with the absorption axis of the neutral polarizer 70, it is blocked and only the red component, the polarization plane of which is parallel with the transmission axis, passes the polarizer 70.
The TN/GH cell 72 is in the ON state, and therefore the light from the polarizer 70 passes the cell 72 without any rotary polarization and hence without any change in color.
When the light having passed the TN/GH cell 72 is projected by the pro~ection lens 68, an image colored in red is reproduced on the screen 70.
In an analogous way, green and blue can be reproduced as is shown in Figs. 8b and 8c, and also white and black can be reproduced as is shown in Figs. 8d and 8e. The excitation condition of the cells in the reproduction of these colors are summarized in a table shown in Fig. 9b. Also in this case, as will be understood from the table, yellow, magenta and cyan can be reproduced by repeatedly switching between two states selected from among the states of Figs. 8a to 8c.
In Fig. 6 there is shown another example of an arrange-ment of polarizers and liquid crystal cells, in which a neutral polarizer 74, a TN/GH cell 76, two TN cells 78, 82 and two color polarizers 80, 84 are employed. Also in this example, all the cells must be provided with matrix electrodes on both sides Df their respective cells in a similar manner to the case of Fig. 5. The TN/GH cell 76 is colored in blue, and the two color polarizers 80 and 84 are colored in red and green, respectively. Further, the absorption axes of the two color polarizers 80 and 84 are at right angles to 2Q each other.
Similarly to the foregoing examples, the color of the TN/GH cell is not limited to blue, but can be freely selected from among the three primary colors. The colors of the two color polarizers must be selected, taking into account the color selected for the TN/GH cell. I~ green is determined for the TN~GH cell, the colors of the polarizers must be selected from red and blue, respectively. There are six combinations f~r the selection of colors for the polarizers and the TN/GH cell.
The excitation condition of the cells of this example is summarized in a table shown in Fig. 9c. Although the operational principle of this example is not shown, it will be understood from the table of Fig. 9c and the analogy of the foregoing description that all the six colors and white and black can be reproduced.
9~2 Still another example of an arrangement of polarizers and liquid crystal cells is shown in Fig~ 7. In this example, there are employed a single color polarizer 86, two TN cells ~8, 96, two neutral polarizers 90, 98 and two TN/GH cells 92, 94. A feature of this example which is different from the foregoing examples is in the use of the two TN/GH cells 92 and 94. The single color polarizer 86 is colored in red and the TN/GH cells 92 and 94 are colored in green and blue, respectively.
Also in this case, the color of the TN/GH cells are not limited to green and blue, but can be freely selected from among the three primary colors. The color of the color polarizer must be selected in view of the colors selected for the TN/GH cells.
The excitation condition of the cells in this example is summarized in a table shown in Fig. 9d. Also with respect to this example, although the operational principle is not shown, it will be understood from the table of Fig. 9d and the foregoing description that eight colors, i.e., red, green, blue, yellow, magenta, and cyan including white and black, can be reproduced.
The effect of the present invention ~ill be discussed, compared with the prior art. The arrangement of the polarizers and the liquid crystal cells shown in Fig. 3 is taken as an example of the present invention, and both the arrangements of E'igs. la and lb are taken as examples of the prior art.
Fig. 10 is a known chromaticity diagram, in which coordinates of red, green and blue reproduced by the above mentioned three examples are indicated. The rightmost correspond to the coordinates of red and the leftmost to those of blue. The coordinates lying therebetween are of green. The area of triangles formed by these coordinates represent the scope of color which can be reproduced by the respective examples. As is apparent from the diagram, the scope of the color reproduction of the present invention is considerably improved, compared with that of the prior art ~2~3898Z
of Fig. la (cf. triangles of a solid line and a chain line in Fig. 10).
In this diagram, coordinates of red, green and blue reproduced by a color CRT in accordance with color signals in the NTSC system are indicated by black dots R, G and ~, respectively. It is to be noted that they do not indicate the coordinate of respective colors which are reproduced by a projector using CRTs. The scope of colors capable of actually being reproduced by a CRT type projector becomes smaller than that indicated by the black dots R, G and B, because it greatly depends on the characteristics and capabilities of dichroic mirrors used in the projector. From this diagram, it will be understood that the present invention reproduces colors which are closer to those reproduced by the color CRT, compared with two other examples. Further, a mark x indicates coordinates of a standard C source.
Referring next to Fig. 11, the comparison of the bright-ness of reproduced colors will be discussed. In the figure, the ordinate represents luminance of respective colors reproduced by the above mentioned three examples in term of the ratio when the value of the present invention is made 1Ø
The abscissa thereof represents a dominant wavelength ~d f the respective colors. Marks indicative of respective values are the same as ones in Fig. 10. For the comparison, values of the dominant wavelength of respective colors reproduced by a color CRT are indicated on the abscissa.
As is apparent from the figure, with respect to blue, for example, the present invention is about 20% brighter than the prior art of Fig. la and about 50~ brighter than that of Fig. lb. With respect to green, the present invention is about 50% brighter than the prior art of Fig. la and about 10% brighter than that of Fig. lb. Further, with respect to red, the present invention is over 30% brighter than the prior art of Fig. la and about 10% brighter than that of Fig. lb. In this manner, as a whole, the present invention is 10% to 5Q~ superior in the brightness of the reproduced colors over the prior art.
Claims (9)
1. A projector having:
a light source for generating white light for projection;
means for collimating the white light generated by said light source;
polarizer means, arranged on an axis of the light, for linearly polarizing the collimated light passing there-through;
liquid crystal cell means arranged with a predeter-mined positional relationship with said polarizer means on the same axis of light and selectively activated and de-activated in accordance with video signals of an image to be reproduced to control the polarization plane of light passing therethrough; and means for projecting light having passed said polarizer means and said liquid crystal cell means to reproduce an image on a screen in full color, characterized in that at least one of said liquid crystal cell means is a Guest-Host type cell which is colored in a color selected from among three primary colors of an additive mixture and the remaining liquid crystal cell means are non-colored twisted nematic liquid crystal cells;
that at least one of said polarizer means is a color polarizer colored in a color selected from the remaining colors and the remaining polarizers are neutral polarizers;
and that a total number of Guest-Host cells and color polarizers is three, each being colored in a different one of the three primary colors in the additive mixture.
a light source for generating white light for projection;
means for collimating the white light generated by said light source;
polarizer means, arranged on an axis of the light, for linearly polarizing the collimated light passing there-through;
liquid crystal cell means arranged with a predeter-mined positional relationship with said polarizer means on the same axis of light and selectively activated and de-activated in accordance with video signals of an image to be reproduced to control the polarization plane of light passing therethrough; and means for projecting light having passed said polarizer means and said liquid crystal cell means to reproduce an image on a screen in full color, characterized in that at least one of said liquid crystal cell means is a Guest-Host type cell which is colored in a color selected from among three primary colors of an additive mixture and the remaining liquid crystal cell means are non-colored twisted nematic liquid crystal cells;
that at least one of said polarizer means is a color polarizer colored in a color selected from the remaining colors and the remaining polarizers are neutral polarizers;
and that a total number of Guest-Host cells and color polarizers is three, each being colored in a different one of the three primary colors in the additive mixture.
2. A projector according to claim 1, wherein said polarizer means includes two color polarizers and said liquid crystal cell means includes a single Guest-Host type cell
3. A projector according to claim 2, wherein one of the two color polarizers is colored in red, the other color polarizer is colored in either green or blue, and the Guest-Host cell is colored in the remaining color.
4. A projector according to claim 3, wherein the Guest-Host cell is colored in blue.
5. A projector according to claim 2, wherein said polarizer means and said liquid crystal cell means are arranged in the order of a first polarizer colored in a first one of the three primary colors, a first twisted nematic liquid crystal cell, a second twisted nematic liquid crystal cell, a second polarizer colored in a second one of the three primary colors, a third twisted nematic liquid crystal cell, a third polarizer which is neutral, and a fourth liquid crystal cell which is a Guest-Host type and colored in a third one of the three primary colors.
6. A projector according to claim 2, wherein said polarizer means and said liquid crystal cell means are constructed by an arrangement of polarizers and liquid crystal cells arranged in the order of a first polarizer colored in a first one of the three primary colors, a first twisted nematic liquid crystal cell, a second polarizer colored in a second one of the three primary colors, a second twisted nematic liquid crystal cell, a third polarizer which is neutral, and a third liquid crystal cell which is of a Guest-Host type and colored in a third one of the three primary colors.
7. A projector according to claim 2, wherein said polarizer means and said liquid crystal cell means are constructed by an arrangement of polarizers and liquid crystal cells arranged in the order of a first polarizer which is neutral, a first liquid crystal cell which is of a Guest-Host type and colored in a first one of the three primary colors, a second twisted nematic liquid crystal cell, a second polarizer colored in a second one of the three primary colors, a third twisted nematic liquid crystal cell, and a third polarizer colored in a third one of the three primary colors.
8. A projector according to claim 1, wherein said polarizer means includes a single color polarizer and said liquid crystal cell includes two Guest-Host type cells.
9. A projector according to claim 1, wherein said polarizer means and said liquid crystal cell means are constructed by an arrangement of polarizers and liquid crystal cells arranged in the order of a first polarizer colored in a first one of the three primary colors, a first twisted nematic liquid crystal cell, a second polarizer which is neutral, a second liquid crystal cell which is of a Guest-Host type and colored in a second one of the three primary colors, a third liquid crystal cell which is of a Guest-Host type and colored in a third one of the three primary colors, a fourth twisted nematic liquid crystal cell, and a third polarizer which is neutral.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62001636A JPH0666018B2 (en) | 1987-01-09 | 1987-01-09 | LCD projection device |
| JP62-1636 | 1987-01-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1288982C true CA1288982C (en) | 1991-09-17 |
Family
ID=11507015
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000556105A Expired - Lifetime CA1288982C (en) | 1987-01-09 | 1988-01-08 | Projector using liquid crystal cells |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4838655A (en) |
| EP (1) | EP0274391B1 (en) |
| JP (1) | JPH0666018B2 (en) |
| CA (1) | CA1288982C (en) |
| DE (1) | DE3888983T2 (en) |
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| US5272553A (en) * | 1988-10-28 | 1993-12-21 | Sharp Kabushiki Kaisha | Projection type liquid crystal display device with twisted nematic liquid crystal layers |
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| JPH04251219A (en) * | 1990-04-09 | 1992-09-07 | Proxima Corp | Stacked-type display panel and manufacture thereof |
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| US3703329A (en) * | 1969-12-29 | 1972-11-21 | Rca Corp | Liquid crystal color display |
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-
1987
- 1987-01-09 JP JP62001636A patent/JPH0666018B2/en not_active Expired - Lifetime
-
1988
- 1988-01-06 US US07/141,144 patent/US4838655A/en not_active Expired - Fee Related
- 1988-01-07 DE DE3888983T patent/DE3888983T2/en not_active Expired - Fee Related
- 1988-01-07 EP EP88100117A patent/EP0274391B1/en not_active Expired - Lifetime
- 1988-01-08 CA CA000556105A patent/CA1288982C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0274391A2 (en) | 1988-07-13 |
| JPS63170614A (en) | 1988-07-14 |
| DE3888983T2 (en) | 1994-10-13 |
| EP0274391B1 (en) | 1994-04-13 |
| JPH0666018B2 (en) | 1994-08-24 |
| DE3888983D1 (en) | 1994-05-19 |
| EP0274391A3 (en) | 1990-01-10 |
| US4838655A (en) | 1989-06-13 |
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| MKLA | Lapsed |