CA1195427A

CA1195427A - Method and apparatus for registering overlapping printed images

Info

Publication number: CA1195427A
Application number: CA000427522A
Authority: CA
Inventors: Yakov Z. Brovman
Original assignee: Harris Graphics Corp
Current assignee: Harris Graphics Corp
Priority date: 1982-05-06
Filing date: 1983-05-05
Publication date: 1985-10-15
Also published as: DE94027T1; DE3373882D1; JPS58217362A; EP0094027B1; EP0094027A1; US4534288A

Abstract

Abstract Method and apparatus are disclosed for indicating and correcting misregister of plural overlapping images produced by a multicolor press. A register indicia (Fig.
3) is used comprising two overlapping sets of parallel lines (R and C), each set being formed in a known position relative to a corresponding one of the images whereby the positional relationship between the sets of lines varies with the positional relationship of the images. The extent of overlap of the sets of lines is dependent upon displacement of the sets of lines in a direction transverse to the lines, whereby the percentage of nonprint area in the register indicia is dependent upon register of the overlapping images in that transverse direction. The percentage of nonprint area is detected by illuminating the register indicia area and measuring the extent to which the area reflects the light. The resulting signal is used to control the register adjustment mechanisms of the multicolor press.

Description

METHOD AND APPARATUS FOR
REGISTERING OVERLAPPING PRIN~ED IMAGES

Background and Field of the Invention The present invention relates to register indicia and to control systems for adjusting the extent to which printed images overlap. More particularly, the inven~ion relates to ~ethod and apparatus for detecting misregister and automatlcally regi.stering two or more printed imagesO
In multi-coloxed printing, color images axe produced by overprinting several images, each printed in dif~erent colors~ To provide ~he proper effect, the several dif~erently colored images should be aligned or "registered" quite precisely atop one another~ To contrvl this, the various pr.intin~ units which toge~ eL make up the multi color press include adjustment mechanisrns enabling one image to be moved relat.ive to another. In order to set these adjustments properly, some technique must irst be provided for detecting misregistration between the differently colored images~
'~

--2~

The sim~Lest method oE detecting misregistration is for the pressman to visually study the printed product to identify the nature and extent of any misregistration between the images. This manual misregis~ra~ion detection 5 and adjustment tecl~nique allows great flexi`~il;cy and permits the pressman to interject his own experience into the registration process. Manual regis~ration adjustment is therefore widely practiced, either alone or in conjunction with automated systems.
Automated systems have some advantages over manual m;sregistration me-thods, principally in the speed with which they operate. Upon the initial start-up of a multi-color press some misregistration generally exists between the various printed color images. All of the 15 printed product produced by the press until this misregistration is corrected is ~iscarded as waste. It is therefore desirable to eliminate misregistration as rapidly as possible in order to reduce the extent of paper waste. Other factors requiring adjustment, notably color 20 ~ensity~ al50 contribute to paper waste.
Because of this, a variety oE automated systems have been provided for detec~ing and correctiny misregistra-tion~ UniEormly, these system require indicia separate and apart from the printed image, per se, in 25 order to simplify the automated process of detecting misregistration. Most generally ~hese indicia take the :~$~

form of individual lines printed by the various units of the press concurrently with the ;mages. The positional relationshlp between the register indicia lines is directly indicati~e o~ the registration between the S corresponding prlnted images. Due to inconsistencles in the printing process, however, the register indicia lines have varying width and density, rendering accurate and repeatable automated determination of their position ~ifficult.
Automatic measurement of the positional relationship between the two register indicia was inherently a dynamic process~ One or more sensor was mounted on the press to detect the passage of the register indicia, and the time between passage of the first and second register indiciums was equated with physical displacement between the two indicia. The measurement was therefore press-speed dependentO
Independently o registration control, color bars have been used in the past for ink density control and press operation diagnostics. The color bars have been printed on the web concurrently with the printing of the image, usually in the margins between the images on the webO No unified system has been used, however, for dealing with both color and registra~ion control; khe two have historically been treated as separate problems with separate printed indicators and separate control processes.

Brief Sumr~ of the Invention It is a general object of the present invention to provide a unified system for measuring and treating registration errors and color errors.
It is another object of t'ne present invention to provide a register error measurement process which is static in nature, in ~hat i~ does no~ rely upon movement between a sensor and the reglster indicat.or in order to detect and quantify register error.
It is another object of the present invention to provide method and apparatus for detecting misregister between two overlapped images produced~ for example, in a multicolor printing operation~
It is also an object o~ the present invention to provide an automated registration detec~ion system which provides accurate and repeatable misregistration detection.
It is still another object of khe present invent;on to provide misregistration detection method and apparatus employing novel register indicia.
~ It is yet another object of the present invention to provide method and apparatus for detecting and correcting misregister employlng a register indicia wherein the percentage of print area in a register indicia area is sensed and used as an indication o. the accuracy of register o~ ~wo overlapped images.
In accordance with one aspect of the present invention a method is provided o detecting misregistration between ~5-two overlapped images. The method comprises the steps of form-ing a first plurality of -transversel~ spaced, su~stantially parallel lines in a first indicia area occupying a known posi~
tion relative to one of the overlapped images, and forming a second plurality of transversely spaced, substantially parallel lines in a second indicia area occupying a ~nown position rela-tive to the other of said overlapped images. The second plurality of lines are oriented substantially parallel to the first plur-ality oE lines such that when the first and second areas overlap one another the extent to which the lines o~erlap one another in the region in which the indicia areas overlap changes with trans-verse displacement between the two lndicia areas. The known position of the second indicia area is selected so -that when the first and second overlapping images are in register, the first and second indicia areas overlap.
According to another aspect, the invention comprises a method of determining the extent of misregister of colors in a multicolor image wherein the percentages of nonprint areas in first and second register indicia fields are each functionall~
dependent upon the extent of misregister of sald colors in a pre-determined direc-tion, and wherein the percentages o:E nonprint area in said first and second fields change in difEerent func-tional dependencies upon changes in the extent of misregister in said predetermined direction~ ~omprising l-he steps of: sensing the percentages of nonprint areas in each of said first and second fields, determining the ratio of the sum of said percen-tages to the difference of said percentages, and determining a `~

-5a said extent of misregister in said predetermined direction in accordance with the results of said ratio determining step.
According to yet another aspect, the invention comprises a method of determining the extent of misregister of colors in a multicolor image having a register indicia area wherein the per-centage of nonprint area is functionally dependent upon misregis-ter of said colors in a predetermined direction, comprising the steps of: illuminating said register indicia area, sensing the amount of light reflected from said area and providing a signa]
having a value which varies therewith, said value thus i.ndica-ting the percentage of nonpr.in-t area in said register indicia area, and utilizing said value to calculate the e~tent of mis~
register of said colors in said predetermined direction.
According to a further aspect, -the invention comprises apparatus for detecting misregister of colors in a multicolor image wherein the measure of a characteristic of a register indicia area is functio.nally dependent upon the extent of mis-register of said colors in a predetermined direction, comprising:
means for sensing the measure of said characteristic of said re-gister indicia area over at least a portion of said area and providing a siqnal indicative thereof, and means responsive to said signal indicative of said measure of said characteristic for c~etermining therefrom the extent of misregister of said colors in said predetermined direction.
Descri~tion of the Drawings The foregoing and other oh~ects and advantages of the present inven-tion will become more readily apparent from the fol-3~
~5b-lowing detailed description, as taken in conjunction with the accompan~ing drawings, wherein:
Fig. 1 is a block diagram of a conventional four color press;
Fig. 2 is a perspective illustration of a web passing through a printing nip, and i5 u.seful in understanding the type of ad-justments to be made in correcting misregistration;
FigO 3 is an illustration of a register indicia in accordance with one aspect of the present invention;
Figs. 4A-4C and 5~-5C are illustra-tions of preLerred forms of printing register indicia, each using two indicia fields, Fig. 6 is a graph indicating the manner in which the printed area of the two register indicia fields shown in FigO 4 change with register error;
Figs. 7A and 7B are. illustrations of a color bar incorporting the regis-ter indicia of Fig. 5 in plural f.ields thereof for detecting circumferential and lateral registration error and cylinder coctcing, Fig. 8 is a plan view oE a scanner assembly for scanning the color bar of Fig. 7;
Fig. 3 is a sectional view of the scanner assembly of Fig. 7 taken alon~ line 9-9 of Fig. 8;
Fig. 10 is a broad blo~k ~iagram of the microcomputer circuitry which responds to the signal.s provided by the scanner assembly of FigsO 8 and 9;
Fig. 11 is a Elow chart illustrating the operations performed by the computer circuit of Fig. 10 in scanning the color bar;
FigsO 12 and 13 are flow charts illustrating the operations performed by the computer to correct register errors;

- ~ -Fi~ is arl elevation view of the ch:ill rolls of the press, showing the placement of two strobe bars in a second embod.iment OL the invention;
Fig. 15 is an illustration of a modifiecl color bar for use with the Fig~ 14 embodiment.

Detai]ed Description FigO 1 is a schematic representation oE a conventional four color printing press 10. The press 10 includes plural printing units 12/ 14, 16 and 18 for printing on a moving web 20 which unwinds from a reel stand 22. As the web 20 moves through each oE the printing nips associated with the printing unit 12-18, it receives a printed i~age having a color corresponding to the color of the ink laid down b~ that printing unit. The imayes printed by the various printing units 12, 14, 16 and 18 overlap one another so as to provide a color imaye. IJpon exiting the last p.rinting unit 18, the web enters tlle o~tput portion of the printing press, including ink driers as well as slicer, older and trimmer units. The produc-t providecl by the output portion 2Q comprises indi.vidual printed signatures containing color imagesO
The fidelity of the color images produced by the press ~5 is dependent in large part on the extent to which the single color images laid down by the various printing units 12-18 are aligned over one anothe~. To control this a register cont.rol system 26 is included. Register control system 26 provides control signals to the three color printing units 14, 16 and 18 for controlling the loca~ions upon ~he web at which their respective printed images are laid down. More particularl.y, the register control system 26 provides control signals for controlling lateral registration, circum~erential registration, and c~linder cocking.
The nature of the printing unit adjustments controlled by these signals can best be seen in Fig. 2, which is a simplified representation of an offset, perfecting printing unit. In this Figure, the web 20 is shown as moving in the direction indicated by the arrow 28 through .a printing nip 30 formed by rolling contact bet~een two blanket cylinders 32 and 34. The blanket cylinders receive ink images from respective plate cylinders 33 and 35~ upon which are mounted the prinking plates (not shown).
BeEore entering the printing nip 30, the web ~0 already has black images 36 formed thereon due to the operation o~ printing un;t 12. The images printed upon the web 20 by the hlanket cylinder 32 should be in precise registry with the images 36. To adjus-t the location of ~5 the printed image formed by the blanket cylinder 32 the printing unit includes mechanisms for moving the plate ~:~$5; ~7 _g_ cylinder 33 relative to the blanket cylinder 32. These mechanisms are entirely convent.ional and will not be shown or described herein for that reason.
One mechanism is controllable to move the plate cylinder 33 in a direction transverse ~o the ,~ vemen~ of the web 20, as indicated by the arrow 38. By controlling the operation of this mechanism the lateral registra~ion of the images may be controlled. Another mechanism is controllable to cause a phase shift oE the plate cylinder 33 relative to the web so as to thereby slightly adjust the longitudinal position o the ima~e placecl on the web

2~ by the blanket cylinder 32. The motions eEfecting circumEerential register are indicated by t'ne arrow 40. A
third mechanism is controllable to cock the plate cylinder 33 relative to the blanket cylinder 32, thereby controllably slcewing the images placed upon the blanket cylinder 32 by the plate cylinder. The direction of this cylinder cocking is indicated by the arrows 42 and 44.
~].1 three of these mechanisms are contro.lled by the register cont.rol sy~tem 26.
Similar mechanisms are provided for con-trollin(3 the plate cylinder 35. These mec~a;lisms, also, are controlled by the register control system 2~ In the interest of simplicity, however, the following discussion will relate only to the adjustment of the upper plate cylinders of each unit. The lower plate cylinders are ad]usted in similar manner~

~10-The re~ister control system 26 determines t'ne extent of misregistration in Later~l, and circumferential directions in order to de~ermine the exten~ to which lateral and circumEerential registration and skew are to ~e adjusted In accordance wi~h tne presen~ invention the register control system 26 determines the extent of lateral and circumferential misregistration, as well as skew, as part of a unified press control process. The system derives not only color and diagnostic information but also register information rom color bars 46 which are printed concurrently with tlle printing of the images on the web 20. The color bar 46 is comprised o 136 square "fields" arranged along a line extending transversel.y between the two edges of the web 20 in an area normally trimmed or otherwise removed from the finished product.
The color bar could instead be formed elsewh~re t of course, such as along the edges of the web. This is not presently preferred t however, since in this event the color bar would not contain color information relating to -~he ink fountains near the center of the web. Each field of the color bar is, for example, approximately 1/4"
s~uare. In accordance with the present invention a number oE these fields are ormed such that register and skew information can be detected dur;ng scanning of the color 25 ~ar in a fashion to be descr.ibed hereinafter. The register fields have plural parallel lines formed therein so as to serve as regis~er indicia.

--ll--In the ~referred embolilnent, each register indicia field I, as snown in Fig. 3 includes two overlapping 5ets of lines, one set R prin~ed in a reference color (usually black) and the other set C printed in a color (referred ~o herein as a "comparison1' color) whose image position is to be adjusted so as to achieve re~ister with the black image. Each set of lines includes plural linear, parallel lines disposed beside one another across ~he field~ The reerence color lines are preferably o~ equal width T~2 and are spaced apart by the same distance T/2. The lines thereore have a "period" T. The comparison colQr lines preferably have the same width and spacing as the reference color ~black) lines.
The two sets of lines are printed so that the lines o~
one are essentially parallel to the lines of the other.
When Eormed thus the percenta~e oE nonprint area in the register indicia Eield varies with register error in a direction perpendicular to the lines. More partîcularly, when the two sets of lines are aliyned so -~ha~ each comparison color line is in register over a reEerence color linel essentially 50% (i.e., tne area between the lines) of the field will be nonpr;nt area. When the comparison color is transversely displaced from this alignment by an amount corresponding to the thickness of 2S the lines, however, essentially 0~ of the field will be nonprint area since the two sets of lines will be completely inteLlaced, leavilly no unprinted space.
Between these t~o extremes tlle percentage of nonprint area varies linearly with displacement.
Tbe percentage of nonprint area in the register indicia field can therefore be used as a measure of the relatlve positions of the reference and comparison colors in a predetermined direction, i.e., perpendicular to the lines in the register indicia field. Moreover, the sen.sitivity of this register indicator to relative positional changes can be selected by selecting the perîod T of the llnes used. If a large number of thin lines are used ~i,e., small T), the indicia ;s quite sensitive since only a small positional change is then required to move the sets of lines from a~ignment to full interlace. If relatively few, thick lines are used~ however ti.e.r large T), the same positional changes will have less impact on the alignment of the two sets of lines.
Although the register indicia field of Fig. 3 is very useful in detecting changes in register error, it ;s difficult to determine actual magnitude and direction of register error therefrom since there is no standard against which to compare the percentage of nonprint area in the field. Consequently r in a preferred embodiment o the present invent;on two different register indicia fields are employed. The actual amount of re~is~er error is then determined b~ comparing the two fields. The -13~

register e-cror meas~rement process wi:Ll be described further hereinafter with reference to F;g. 6. A presently preferred form of the two indicla fields will Eirst be described with reference to Figs, 4A, 4B and 4C/ however.
In Fig~ 4A two exemplary reg.ister indicia fields Fl and F2 of the color bar, are shown. Figs. 4B and 4C show the reference and comparison color components separatelyO
As can be seen in Fig. 4B, wherein the shaded portion indicates the portion which is printed in tlle reEerence color, the same set of lines is produced in both fields in the reference color. In each of the fields Fl and F2 the indicator includes plural lines, each extending the entire width of the Eield, and having a line width which is substantially equal to khe spacing between the lines. The areas between the plural lines are unprinted.
As can be seen in Fig~ 4C, wherein the shaded portion indicates t.he area to be printed in the compar.ison color, the images printed in the two fields Fl and F2 are siml:Lar to each other but are transversely offset by T/4. ~ach consists of plural lines extending across the widths of the respective ~ields, w;th the lines havi.ng the same spacing and width as the reference color lines of Fig.
4B. The comparison color lines in field F2 are transversely displaced by T/4 with respect to the ~5 comparison color lines in 'leld Flo When the reference and comparison colors are in proper register, the plural 1 'I -lines in field ~1 are displaced sligh-~ly downward with respect to the reference color lines, whereas the comparison color lines in field F2 are displaced sliyhtly upward with respect tc the reference lines. The two fields Fl and F2 then appear as shown in Fig. 4A~
As seen in Fig. 4A, perfect registration between the two colors results in the extent of overlap oE tlle colors in the first field (Fl) being equal to the extent of overlap of the two images in the second field (F2). In field Fl the plural lines of ~he comparison color protrude below the corresponding lines in the reference color by an amount corresponding to one quarter of ~he thickness of the lines (i.e., to T/8), whereas in the second field F2 the plural lines of the comparison color rise above the corresponding lines in the reEerence color by the same amoun~.
The period T oE the lines i5 rather ~arge in -the Fig.
4 example, Of course, the period T of the lines may be selected to provide any desired indicia sensitivity. When a smaller period T is employed, a larger number oE lines will be present in the ~ields. When a larger period T i5 employed, a smaller number of lines will be present in the fields. Figs. 5A~ B and C correspond with Figs. 4A, B, and C but represent a situation where a larger T is selected such that fewer reference and comparison color lines are present in each field.

~l~s~ 7 Register erro.r in a directio~ perpendicular to the direction of extension of the comparison color and reference color lines can be calculated in accordance with the percentage of nonprint areas in the two fields Fl and F2. ~rom Fiy. 4A it is apparent that the percentage of nonprint area oE the two fields Fl and F2 is equal when the two images are in regis~er. When the co~arison image is displaced upward (from the position shown in FigO 4~ by an amount less than T/8 with respect to the reference color, the percentage of nonprint area in field Fl will increase whereas tha-t in field F2 will decrease. The percentage of nonprint area in field Fl will then be greater than the percentage of nonprint area in field F2.
When, on the other hand, the comparison color is displaced downward (from the position shown in Fig. 4) by an amount less than T/8 with respect to the reference color, the percentage of nonprint area in field Fl w;ll diminish~
whereas that in field F2 will increase. The percentage oE
nonprint area in field F2 will then be greater than the percentage of nonpr.int area in field Fl.
T'ne relationship between misregister and the percenta~e of nonprint area in the t~o fields is shown graphically in FigO 6, where the curve Fl indicates the percentage of nonprint area in field Fl, and the curve F2 represents the percentage of nonprint area in field F2.
The fields Fl and F2 achieve maximum percentage of ~5~ 7 nonprin~ area at misreg;sters of -t T/8 and ~ T/8, respectively. At these displacements the sets of lines in the comparison color in one fie]d are aligned wit'n the sets of lines in ~he reference color. The percentage o-E
5 nonprint area decreases linearly from ~hese peaks until reaching a value of 0 at displacements wherein the lines in the comparison color completely block the nonprint area in the reference color ~iOe., the sets of lines are interlaced~ This occurs at a displacement o plus and minus 3T/8 for the fields F2 and Fl, respectively.
The magnitude and direction of register error can be directly calculated in accordance with the percentage of nonprint area in each of the two fields Fl and F2. I~ we presume that the reLerence color and the comparison color are misr~gistered by an amount Xl, ~hen the percentage o nonprint areas in the fields Fl and F2 will be Yl and Y2, respectively. But:

Fl = B -~ AX (l) F2 = B AX (2) where B is the Y axis intercept value oE both unctions~ i.e~, the percentage of nonprint area in each ~ield when the re~ister error X

is equal to zero, '7 and A is tlle slope of the linear portion of function Fl in the region between X = 0 and X = -~T/~, and t'ne negative oE the slope o~
F2 in the same region.
But since Fl(X13 = Yl and F2(Xl) - Y2, then-Yl = B -~ AXl ~ ) Y = B - AX (4) Both of these equat~ons are dlpendent upon unknown constants B and ~, hence ~he register error Xl may not be readily calculated from either, by itselfD For this reason it is dificult to calculate absolute register error based solely upon the percentage o~ nonprint area in a single register indicia field. The Y axis intercep.
value B can be shown to be equal to 3AT/8, where A is again the slope and T is the period of the lines in fields Fl and F2. When this is substituted into e~uations (3) and (4~ the unknown term "B" can be elimina-ted. The unknown l'A", however, is still present. By manipulating these ~wo equations, however, we find tha-t:

X = (Yl_ ~2) 3T
1 (~1 2) T~e unknowns A and B do not appear in this equation.

The register error X is instead expressed solely in terms of the known variables Yl and Y2 and the known constant T. Furthermore, the result of the equation will be the same even if the "percentage of nonprint area"
terms ~1 and Y2 axe multiplied by the same galn constant, as might occur during the process of determining the values of these ~erms. This is because such arbitrary gain constants will appear in both the numerator and denominator of equation (5) 9 and will therefore cancel.
The foregoing equations hold true, however~ only for misregistration errors in the range of -~ T/8, Outside of this region (region I) the slope of one or the other of the lines changes, hence equations l13 and t2) no longer apply. In the region (region II) between registration errors of +T/8 and ~3T/8, the equations for functions Fl and F2 are:

Fl = 5AT - AX (6) F2 = 3AT - AX (7) Equation (7) is the same as equation {4~, except that the Y axis intercept value B is expressed in terms of the 20 slope ~ and line period To If we presume that F15X2) - Y3 and F2(X2~ -Y4, then:

Y = 5AT - AX (8)

3 8 2 Y = 3AT - AX l9)

4 ~ ~

These equations may again be manipulated to derive a resulk which is independent of the slope ~ and which ~s simila.ely independent of ar'oitrary gain constants. Thus, by manipulating equations (8) and ~9) we get D

= T - ~Y3 ~ Y~ T (10 ~ 2 (Y3 - Y~) 8 This same equation is also applicable to registration errors in the range -T/8 to ~3T/8.
Equations (5) and (10) permit identification of the actual registration error X in dependence solely upon the percentage of nonprint areas in the two fields Fl and F2 and the known period T sf the lines. The percentage of nonprint area in a given field can be readily ~etermined by measuring the amount of light refle~ted from the field. Th.is process will be described hereinaEter.
Since the two equations (5) and ~1.0) provide different X values for khe same Y values/ it is necessary ko determine which of the two equations to apply Eor any given pai.r of Y valuesD This can be determined by utilizing the measured Y values to calculate an X value Erom equation 15~ the X value thus determined llas an absolute magnitude less than T/8, then the X value is accurate. If the absolute value of the X value is above T/8, however, then the value thus determîned is inaccurate and a recalculation must be done with equation (lO~o Using the relations of equations (5) and (10)l register errors in the range of -~ 3T/8 to - 3T/8 can be quantified If T is large, the range is similarly large and thus gross register errors can be salculated. If T i5 small, however, small register errors can be calculated with greater precision. For this reason, it is presen~ly preferred that two pairs of fields having different T
values be usedO Each pair of fields i5 referred to hereinaEt~r as one "digitl' of register indicator. One digit has a large T value and is used for coarse register control~ The other digit has a small T value and is used for fine register control~
In accordarlce with the present invention, the registration indicia are utilized to detect lateral and circumferential misregister~ as well as cocking, in a multicolor press simultaneously with detecting color variations and diagnosing press conditions. This is possible because the register indicator which has been described can readily be Eormed as part of a color bar.
Register error detection and measurement can therefore be accomplished during the scanning of the color bar. (The register indicia described could, however, be Eormed elsewhere on the web, including within the printed image.) To accomp]ish this, the color bar 46 (Fig. 2) is designed to include plural rey;ster indicia of the type described above with respect to Fig. 5. ~he color bar is shown in greater detail in Figs. 7A and 7B~ As described previously, the color bar 46 includes 136 square fields disposed adjacent one ano~her in a line extending transversely between the two edges of the web.
The 136 fields are grouped into nine register bands/
two diagnostic bands, and twelve color bands. The color bands alternate with the eleven register and diagnostic bands across the color bar. ~ach color band includes four fields, each field being printed in a different solid color (i.e~, without screens or lines). The register ~ands, on the other hand~ include eight fields, four of which are devoted to two digits of registration indicial and four of ~hich contain lines and screens in the color to which the registration indicia for that band relate (i.e., in the comparison color).
~ig. 7~ shows the conten~s of the irst 12 fields oE
the color bar~ The first four fields of the color bar are solid black, cyan/ mayenta, and yellow, respectively.
These our fields represen~ one color band. Fields 5 and 6 represent one "digit" o~ the register indicator for regis~ering ~he cyan color in a circumferen~ial direction~ These two fie1ds may, for example, be ~a~

identical to the fiel~s sho~n in Fig. 5, and have a line thickness of one~tenth of an inch such that T=~2"~ This register digit is used for coarse register controlO
Fields 7 and 8 are 80% and 20~ screens in the cyan color, whereas fields 9 and 10 are different thickness lines in the cyan color. Fields 11 and 12/ which are the last fields in this register band represent the second "digit"
of registration indicator. In this second digit the period T of the lines used is substantially reduced (e.g.
equal to one-hundredth of an inch such that T=.02") so that the indicator is much more sensitive to small register errors than is the first digit. The second digit is used for fine register control. The reference and comparis~n sets of lines in the two fields of the second digit are again displaced from one another by ~ T/8 and -T/8 , as described with reference to Fig~ 4.
Fig. 7B illustrates schematically the arrangement of the 11 reglster and diagnostic bands and the 12 color bands which separate them. In this Figure the cross-hatched portions each represent a color band similar to the first four fields of the color bar. The register bands, on the other hand, each includes eight fields arranged similar to the cyan circumEerential register band illustrated in FigO 7A (i.e~ t fields 5-12~. The nine register bands are indicated in Fig. 7B as Bl~B3, BS-B7, and Bg-Bll. The comparison color used ;n each register '7 band correspollds to the color to be registeredJ and the orientation of the lines is perpendicular to the direction in whicn register is being detected. The bands B4 and B8 are diagnostic bands whose ~ields include colors representing mixtures oE the pure colors which are laid down by the various printing units.
The first three regis-ter bands and last three register bands ~B1~3 and B9~Bll~ are used ~or detecting circumEerent;al register error and cylinder cocking. In bands Bl and ~11 the comparison color is cyan. ~n bands B2 and B10 the comparison color is magenta and in bands B3 and B9 the comparison color is yellow. In all six of these fields the orientation of the llnes in both digits of the registration indicia is parallel to the orientation of the color bars ~i.e., transverse to the web)) whereby register error is detected in a circumerential direction, a~ indicated by the arrow 40 in Fig. 2. Bands B5, B6 and B7, which are the center three bands o~ the color bary are used Eor detecting register error in a direction transverse to the web, and therefore are referred to as lateral re~ister bands. In these bands the indicia Eields are each rotated 90 so that the lines in the various register indicia diglts are oriented in a direction perpendicular to that shown in Fig. 7, and thus run parallel to the edges of the web. In register band B5 the comparison color is cyan, whereas in bands ~6 and B7 the comparison colors are magenta and yellow, respectively.

-~4-Gener~lly statedg the color bar is scanned by se~uentially illuminating each field ~ith electromagnetic energy (usually light, eitller visible, infrared or ultraviolet) and measuring the amount of energy re1ected from the field. The frequency of electromagnetic energy to be used is selected such that the energy is absorbed by the .ink which forms the indicia and reflected by the background. The selection of the appropriate frequency range may be made by using a source which radiates only at those frequencies, a detector which is sensitive to only those frequencies, or by placing appropriate filters at some point in the path of the energy. If the field is entirely covered by the indicia~ very little of the electromagnetic energy is reflected~ If, however~ the field is entirely free of printed indicia, the background is completely exposed and a relatively great amount of the energy is reflected. The measure of reflecked energy is therefore indicative of the extent to which the indicia covers the background on that field. In the example being 20 described/ the background is unprinted. Consequently, the measure of reflected energy is also a measure of the percentage of nonprint area in the field.
It will be noted that t7ne process for reading each field of the color bar is essentially static in nature;
the amount of reflected energy is measured at a given instant in time, rather than over a finite period while -25~

the indicia moves relative to the sensor. Furtnermore, the value obtained is representative of a characteristic o~ the entire area, rather than a distance or dimension measurement of details within the field.
An automated system is used to scan ~he color bae.
One method of accomplishing this, which will be described later herein, is to sense the percentage of nonprint areas in the various digits of the registration bands at some point on the press, while the web is still intact. A
second is to scan the color bars only after the web has been sectioned into signatures and the si~natures delivered at the output of khe press. In this second method, the signatures are carried to a scan table where they are aligned underneath a scanning device for scanning the various registration bands either simultaneously or se~uentially. One mechanisrn for implementing this second method is illustrated and will be described hereinaEter with respect to Figs. 8~10.
Fig. 8 is a plan view of a scanning rnechanism, whereas Fig. 3 is a sectional view taken along line 9-9 o~ Fig.
8. In these Figures~ the scanning mechanism 100 is shown as including a scanning assembly 102 and a guide channel 104. The scanning assembly 102 includes a rectangular base plate 106 having a window 108 fcrmed therein~ and a ~5 scanning head 110 disposed over the windowO The scanning head includes plural connections for fiber optic cables which both illuminate and observe ~he color bar ~hrough the window 108. The guide channel 104 is a planar bar having a width which is s;mllar to the width of the base plate 106 of the scannlng assembly 10~ The scanning assembly 102 rests atop ~he guide channel 104 and slides back and forth in a longitudinal direction over the guide channel~ The guide channel 104 has opposed lateral edges 112 and 114 which are curled upwardly and inwardly so as - to confine the opposiny edges of the base plate 106 of the scanning assembly 1020 The guide channel 10~ also includes a centrally disposed elongated window 116 which extends mos-t of the length of the bar and is formed generally in lateral register with the window 108 of the base plate 1060 The window 11.6 is sized such that a signature bearing a color bar as shown in Fig. 7B may be located beneath the guide channel 104 in alignment with the window 116, whereby the scanning assembly 102 may be manually moved baclc and forth over the opening to thereby scan each anA every field oE
the color bar. The scanning head 110 protrudes beneath the lower surface of the base p:Late 106 into the window 115 o the guide channel 104. The scann.ing head 110 protrudes far enough into window 11~ that its bottom surface is nearly flush wi.th the lower surface of the 25 guide channel 104.
The scanning head 110 includes two optical assemblies mounted side by side over the window 108 in the base plate '7 -27~

10~. ~ach op~ical assembly 1~ and 120 of the scanning head 110 has a hemispherical chamber formed therein which opens ontQ the window 116, but which is otherwise sealed from external light. The chambers in the two optical assemblies 118 and 120 are sealed from one another, as well. Each optical assembl~ 118 and 120 further includes three tapped openings therein Eor the connection of respective ~iber optic cables such that the cables are in optical communication with the correspondiny chamber o the optical assembly.
When affixed to the respectivè optical assembly of the scanning head 110, each fiber optic cable i5 directed toward the center of the window 116 whereby it views the various fields o~ the color bar positioned underneath the guide channel 104 as the scanning assembly 102 is moved back and forth thereover~
More particularlyl the fields of view of all three optical fibers coincide with the circular area delineated by the dotted line 121 in Fig. 4A. In the embodirnen-t being described, the center optical fiber 122 oE optical assembly 118 is attached to a light source ~not shown), whereby the field locatecl within the field of view of that portion of the scanner assembly is illuminated there~yv The remainincJ two optical fibers 124 and 126 are attached to photosensitive detector assemblies 128 and 130 (Fig, 10) 7 respectively. Similarly, the center optical fiber of ~$~ '7 the second optical asseml~ly 120 of the sc~nner head is connected to an optical source, and the other two optical fibers 132 and 13~ oE t'nat assembly are connected to associated detector assemblies 136 and 138. The fiber optic cables have been omit~ed from Fig. ~ to .simplify the drawing.
The four detector assemblies are all similar, each including a corresponding filter 140-143 and photosensitive element 144-147. The four filters 140-143 are the compliments of the four colors printed by the multi-colored press~ 5ince the four proper colors printed by the press are mage-nta, cyan, yellow and black, the our filters are green, red, blue and yellow. When a re~istration indicia such as that shown in Fig. 4A is viewed through a ~ilter which is the compl.iment of the comparison color, both of the sets of lines appear to be black. Consequently, the amount of reflected light can be used as an indication of the percentage oE nonprint area within the field of view of the filterO
To take readings of the amount of reElec-ted light from each field as viewed through each of the complimentary filters, the scanning assembly 102 .is moved by hand from one extreme end of the window 116 to the other. ~s the scanning assembly 102 moves along the window the outputs of the four detector elements 144-147 are per~odically sampled by a microcomputer (Fig. 10), with the resu~ting R~ 7 sampled values represen~ing the "Y" val~e.s reEerred to previously with respect to Fig. ~.
In the embodiment currently being describe~ the outputs of the four pho~osensi~ive elements :L44-147 are connected to respective input lines of an analog input interface 1480 The interface 1~8 includes circuitry for sampling the analog signals provided by each of the photosensitive elements, under control of the - microcomputer lS0. The sampled analog levels are converted to corresponding digital sgnals by an analog-to-digital convertor included within the inter~ace~ The resulting digital signals are provided to the microcomputer for use in determination of register error. The analog input interface 148 and microcomputer 150 are two elemen~s of a conventional measurement and control processor such as the ~ewlett Packard HP2250.
Other elemenks of the measurement and control processor include a digital input interface 152 and an analog or digital output interface 154~ Since these elements are en~irely conventional and are readily available, the~ will not be described in detail he.rein~
In the present embodiment, the microcomputer 150 is triggered to sample the outputs of the optical detectors 144-147 by trigger signals generated from t.iming marks 156 aligned adjacent the wîndow 116 in ~he guide ~hannel 104 ThP timing mark~ 156 are inscribed on the guide channel such that, when a color bar is properly a:Ligned w;t'nin the window 116, ~he timing marks are aligned above the centers of corresponding fields of the color bar.
Two other marks, referred to as start and stop marksr are inscribed below the window 116. These marks define the Eirst and last fields in the color bar, and are used to initiate and conclude a scan of the color bar.
Conventional indicia sensors 162 and 164 are moun~ed on the base plate 106 of the scanning assembly 102 in order to detect ~he passage of the timing marks 156, 158 and 160. The sensors may, for example, be similar to those used to sense the bar codes now provided on most consumer products.
The sensors 162 and ].64 are located in transverse alignment with the second optical assembly 120 of the scanning head 110. Consequently, ea~h time one of the timing marks 155 is detected by the timing mark sensor 162, the second optical assembly 120 is aligned above a corresponding one of the fields oE the color bar. The Eield of view of the firs~ optical assembly 118 of scanning head 110 ls displaced from the field of view o second optical assembly 120 by a distance correspondln~ to the width of four f:ields. Consequently, the second optical assembly 120 is located in optical alignrnent with ~5 one of the fields each time the first optical assembly :L18 is located in optical alignment with one of the fields Since it is deslrable to have each of the assemblies 118 and 1~0 scan eac'n of the ~ields o the color bar, the scanner assembly 102 is moved over a total number ields which is four greater ~han the actual number o~ fields in the color barO Consequen~ly, there are 140 of the timing marks 156, four more tha-n the to-~al number of fields.
This insures that each op~ical assembly views each field of the color bar, even though the two assemblies are displaced from one another.
In operation, a slgnature S printed b~ the press is taken from the press output and aligned under the guide channel 104 such that the color bar is in registra~ion with the window 116 therein. More particularlyr the color bar is aligned within the window 116 such that each of the ~iming marks 156 is aligned over a center of a corresponding one of the ~ields, with the start mark 158 being aligned beneath the center of the first field in the color bar. In this position the last ~ield of the color bar is displaced rightward (as viewed in Fig. 8) by our fields with respect to the star~ mark 158.
A~ter having been thus positioned, the gu;de channel 104 is clamped in its position over the signature S by clamping elements not shown in the Figures. The scanner assembly 102 is then moved to the ~ar left of the window 116 t whereby the timing sensors 162 and 164 are located leftward (again a5 viewed in Fig. 8) of the start mark 158 ~5 ~'7 and the leftward most one of the field tirnin~ ~arks 155.
The opera-tor sets one of the switches of the switch array 155 to a position indica~ing w'nether tlle color bar to be scanned is from the top or bottom oE the web. The operator then depresses another of the switches of the swikch array 1S5 to initiate the acquisition of data. The operator thereafter moves the scanner assembly 102 along the window 116 until it reaches the extreme right end of the window.
Fig. 11 is a flow chart of the steps performed by the microcomputer 150 .1uring the scanning of a color barO As the scanner assembly 102 is moved rightward~ the timing sensor 164 first de-tects the start timin~ mark 1580 In step 184 the microcomputer waits for the start mark, then proceeds to step 186 to wait for the field timing marks.
Each time the field timing mark sensor 162 detec.s one of the ti.-ning marks 156, it proYides a pulse to the microcomputer 150. In response to each pulse (step 188 the microcomputer 150 reads the values oL ~-~ach oE the analog signals provided by the sensors 144-147 through the analog input interface 14B. The microcomputer determines which o~ the fields is being scanned by each optical assembly 118 and 120 of the scanner head 110 by keeping track o the number of the timing marks 156 which have passed the ~iming sensor 162 since the start mark 158 was detected. The analog values read by the microcomputer 150 from each Lield o.~ the co].or bar are stored in corresponding locations in memory for later processing.
The microcomputer then increments the timing mark counter (step 190) and returns to step 186.
Eventuall~, the scanner assembly 102 reaches the point at which the timing sensor 164 detects the s~p mark 160, thereby indicating to the microcomputer 150 that the entire color bar has been scanned. When the microcomputer xeceives the pulse from timing mark sensor 164 (step 192) it checks the value of the timing mark counter tstep 194). If the correct number of fields timing ~arks 156 were detected between the times of detection of the start timing mark 158 and the stop timing mark 160, the microcomputer 150 validates the sean (step 196) and advises the opera~or oE -tnis validation by an appropriate indication, e.g., the illumination or darkening of an indicator lamp, etc~ If the total number of timing marks counted between the times of oceurrence of the start and stop marks 158 and 160 is nat correct, however, (due, for example, to inadvertent momentary movement of the scanning head 102 in a lefward di.rection) the scan will not be validated by the microcomputer. Instead, the microcomputer will lndiclate that an error has taken pl~ce (step 198)~ In this event the operator should repeat the scanning process, as outlined aboveO
The data thus acquired in th;s process is sui-table for both register control and color control, as well as or -3~

diagnosing such press problems as picking-up paper and inlc disseminat;,on. Thus, total press control is achieved in a single, unified process oE data ac~uisition and processing. ~he manner in which the acquired data is used for color control and diagnostics is irrelevant to the present invention and therefore will not be described herein.
Fig. 12 is a flow chart illustrating gene~ally the registration procedures performed by the microcomputer 150 upon the completion of scanning of the color bar in the manner descri,bed above. The microcomputer jumps into this procedure at step 200 when the operator initiates the procedure by depressing an appropriate switch associated with the switch array 1S5~ In step 202 the microcomputer fetc'nes the register indicia field data relating to the first color to be reyi~tered from memory. This data is the data obtained during the scanning procedure detailed above.
In step 204, the microcomputer determines la-teral register error El from the data fetched in step 202.
(The manner in which this register error is determined will be described in greater detail hereinafter with reference to Fig. 13~) For examplet if the color cyan is being registered, the register error is determined by processing the data obtained from scanning register band B5. This register error value will later be applied to '7 the lateral register error control mech~lnism ~or correction of lateral registration. In step 208 the microcomputer determines the circumferential errors ECl, EC2 on the l.eft and right sides of the color bar as viewed in Figs. 7~ and 7Bo In step 210 circumerential error is determined by averaging the two terms ECl and EC2. The averaging of ECl and ~c2 eliminates the influence of skew on the circumferential error determination.
~kew of the color image being registered is detected in step 214 by subtracting the circumferential re~.ister error terms ECl and EC2. If khe blanket cylinder is properly cocked, the circumferential errors on -the left and right side of the color bar will be the same whereby the skew error value ~s will be e~ual to zero. The extent to which thi.s terms difers from zero corresponds to the extent of image skew.
Having thus determined circumferential reg,ister, lateral register, and skew error values for one color, the microcomputer proceeds on to condi-tional step 218~ If error values for all three colors have now been determined, the microcomputer proceeds on to step 220.
If, on the other hand, error values must yet be determined for one or more other colors, the microcomputer jumps instead to step 222l wherein data for -the next color to be registered is fetched from memory~ Ater step 222t the -~,6-microcomputer repeats steps 204-214 ln order to find updated reglster and skew error vallles for the new color.
When all colors have been processed, the microcomputer proceeds on to step 220, wherein the updated regis~er values are read out to the press. The var.ious adjustment mechanisms associated therewith respond by adjusting the register and skew of the associated unit in accordance with the error signals~ The updated register values are outputted on twelve output lines 221 through the analog or digital output interface 15~. The nature of these signals (dîgital or analog, voltage and current values) will of course be dependent upon the requirements of the various adjustment mec'nanisms being controlled. T'ne microcomputer also provides an upper/lower deck control signal indicating whether the upper or lower deck is to respond to the control signals being prov.ided. The value of this control signal is dependent upon whether the color bar which was scanned originated from the top or bottom o the web.
After waiting an appropriate interval to allow the updated register and skew values to set into the press, the pressman takes another siynature Erom the output o the press and scans the color bar with the scan.n.ing mechani.sm described above with respect to ~igs, $ and 9 r and then initiates microcomputer adjustMent of the register of the press. This process continues until the registration oE the press is acceptable to the pressman.

Fig. 13 illustrates in grea~er ~etail t'ne operatlons perEormed by t.he microcomputer in determining register errors~ whether circumferential or lateral. -The steps illustrated in Fig. 13 are performed in each of steps 204

5 and 208. In step 230~ the microcomputer fetches the 11y~7 readings from two fields Fl and F2 of the ~irst dig.it of the variable being registered, T'nus, if circumEerential register is being adjusted, then data .LrOm tlle two fields Fl a~d F2 such as shown in Fig. 7 will be Eetched from memory.
From the scanning procedure described previously with respect to Fig. 11, it is apparent that each of the fields of the color bar is viewed through each of four different filters 140-143 of Fig. 9. Consequently four different readin~s are available for each field of the color bar.
In detecting misregister, the values o interest are those produced when viewing the fields through the filter which is the compliment o the color being registered. Thus~
for example/ if magenta .i~ being registered, then the data Eetched in skep 230 will be that data which was acqu.ired through a green filter, since green is the compl.iment of magenta. As viewed through this filter, both the magenta and the black image will appear black, whereby the percentage of nonprint areas in the two fields may be used ~5 to determine register ~rror in the fashion described heretofore with respect to Figs. 3 and 4.

~S~27 In step 232 the microcomputer calculates register error as a functlon of the percentage oE nonpr:int areas in the fields Fl and F2. The calculations performed by the microcomputer in determining this error have been described above with respect to equat.ions (5) and (10) and will not be repeaked Eor that reason~ Beore using equatlons (5~
and (10) the measured Y values are corrected to remove an offset value YO introduced by the measurement process~
The mathematical manipulations leading to equations (5) and ~10) presume that tlle measured Y value will be zero for a register indicia field where the reEerence and comparison color lines are perfectly interlaced. OEten, however, the measured Y value (which will be referred to as YO) will not be zero under these conditions. Worse, the extent to which the YO value deviates from zero will not be fixed, instead varying with the type and ~ensity of the ink used, the extent to which the press is l'picking up paper" and other factorsO
To relnove the resulting YO oEfset it is presently preferred that the m.icrocomputer determine a YO value for each register band, and then subtract the YO value ~hus determ.ined from each measured Y value for that register bandO When the Y values have been corrected in this fashion, e~uati.ons ~5) and (10) can be used as described previously.
The ~O value for each register band can be determined by several methods~ Tne presently preferred method is to average the Y readings taken Erom the fields pr;nted in the solid reference arld comparison color inks.
The resultiny value should correspond to the YO value, which is after all the Y value measured for a fie]d which is printed half in the reference color and half in the comparison color.
To accomplish the ~O value determination the microcomputer first fetches ~wo ~ values from memory relating to an adjacent color band. The two Y values chosen are thQse measured for the fields which are printed in the reference and comparison colors, as viewed through a complementary filter. These two Y values are then avera~ed to get YO.
For example, the two Y values selected for register band Bl (where the reference color is cyan) are those Erom fields 1 (solid black) and 2 (solid cyan) of the color band, as measured through the red filter (since red is the complement of cyan)~ These two Y values are then averaged b~ adding them together and dividing their sum by two.
The resulting value is YO for register band Bl.

The register error calculated throu~h use of equations (5) and (10) i5 compared with a limit in step ~34 to de~ermine whether or not the error is small enough that the register error indicated by the second digit is valid. If the register error is in the range of plus or mi~us 3T/8 (T being the period of the lines in t~le second ~S ~,'7 ~40-.

digit), tlle microcompuker proceeds on to step 23~, wherein the data rela~ing to fields Fl and F2 of the second digit is fe-tc'ned for calculaLing a more refined reg;s~er error indication. This procedure is essentlally the same as that conducted in step 232, except t~at the period T of the lines is much srnaller~ Thus, the exror in this case becomes the error calculated in step 238, rather than that calculated in step 232. After calculating the error in t.his fashion, the microcomputer returns to the main program (F.ig. 12).
In the emboæiment which has been described above, the registra~ion is accomplished by a t'm~n-in-the-loop"
feedback arrangement, wherein a press operator is relied upon to obtain a copy o a signature Erom the press output and to then insert the signature into a device for scanning the color bar so that data relating to circumferenti.al and lateral register and skew may be obtained therefrom. Alternatively~ thls operation may be perEormed in a completel~ automatic feedback loop. In such a s~stem ~he devices for sensing ~ne percelltage oE
nonprint areas in the register indicia fields are loca-ted upon the press itself/ whereby intervention by a press operator is not required Fig. 14 illustrates one embodiment wherein the sensing o~ ~he regis~er indic.ia is performed in the vicinity of two chill rollers 250 and 252 located at the output 24 -41.-~Fi.g. l) o~ the press. In this embodiment a first strobebar 254 is located adjacent chill roll 250 and second strobe bar 256 is located adjacent chill roll 25~. 5ince the web 258 is rounded around the chill rolls 250 and 252 in an S-wrap configuration, the upper surEace of the web is exposed around chill roll 250, whereas the lower surface of the web is exposed around chill roll 252. The two strobe bars 254 and 256 therefore view di~ferent surfaces of the web and provide data for registering the upper and lower declcs, respectively, of each printing unit~
The strobe bars 254 and 256 are longitudinal bars extending essentially the entire width of the web 2S8.
Each scanning bar ~54 includes four optical assemblies for each of the register bands, where each o~ the assembli2s is positioned laterally across the web so that it is aligned with a corresponding one of the four fields included in the two digits of that register band. Since there are a total of nine register bands; each including four fields of register indicia, there need only be a total of 36 sensors associated with each oE the scanning bars 254 and 256 in order to obtain register in:Eormation.
Preferahlyr however, other sensors will be included for obtaining color and diagnostic inEorma-tion from other fields of the color bar. The color used as the comparison color in the field of view of each of the sensors is known, so that the sensor need include only a light source ?J~9 and a s.ingle p'notosensitive sensor. The sensor includes a single filter corresponding to the compliment of the co.llparison color being viewed by t'nat sensor~
The color ba.rs which are scanned by the strobe bars 254 and 256 are aligned under the color bars only for a brief moment as the web 258 travels around the chill rolls. The color bar may be modified slightly in order to simplify the "on the fly" data acquisition from the color bar. One possible altered color bar configuration is shown in Fig. 15. The principle distinguishing feature of this altered con~iguratlon is the inclusion of a timing mark 260 laterally adjacent the color bar 46. This laterally extending timing mark 260 is sensed by an indicia sensor mounted at the end of each strobe bar 254 and 256. The indicia sensor triggers the microcomputer 152 each time the timing mark 260 is sensed. The microcomputer respollds by reading ~he outputs from the sensors disposed along the strobe bar. rrhe microcomputer may be programmed to read all of tlle sensors eac'n time a trigger pulse is received or, alternatively, to read the sensor sequentially upon secluential trigyer pulses. At the time of sensing of this tlming mark, the fields o view 262 of the sen.sors are in proper circumEerential alignment with a ~orresponding E.ield vf the color bar 46.
The color bar 46 preferably has expanded circumEerential dimensions so that the fields of vie~ 262 of the sensors will remain within its boundaries during the reading process, regardless of skew of the color bar relative to the strobe bar ~54, 256, minor timing errors, etc. After the register data is acquired "on the fly", the remainder of the register operation is as de.scribed heretofore.
Although t'ne invention has been described with respect to a preferred embodiment, it will be appreciated that various rearrangements and alterations of parts may be made without departing from the spirit and scope of the present invention, as defined in the appended claims~

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of indicating misregister between two overlapped images, comprising the steps of:
forming a first plurality of spaced lines in a first indicia area occupying a known position relative to one of said two overlapped images, said lines being substantially straight and disposed substantially parallel to one another, forming a second plurality of spaced lines in a second indicia area occupying a known position relative to the other of said overlapped images, said second plurality of lines being substantially straight and oriented substantially parallel to one another and to said first plurality of lines such that when said first and second areas overlap one another the extent to which said lines of said first and second areas overlap one another changes with displacement between said two indicia areas in a direction transverse to said lines, said known position relative to the other of said overlapped images being selected so that when said overlapping images are in register said first and second indicia areas overlap, detecting the extent of overlap of said lines of said first and second indicia areas, and utilizing said extent as a measure of misregister of said overlapping images.

2. A method as set forth in claim 1, wherein said step of forming said first plurality of lines comprises the step of forming said first plurality of lines such that said straight lines are of equal width and are transversely spaced from one another by a distance which is substantially the same as the width of said lines.

3. A method as set forth in claim 2, wherein said step of forming said second plurality of lines comprises the step of forming said lines of width and spacing substantially equal to the width and spacing of said first plurality of straight lines.

4. A method as set forth in claim 2 wherein said step of forming said second plurality of lines comprises the step of forming said lines to have substantially the same width and spacing as said first plurality of straight lines and in a location relative to said other of said overlapped images such that when said overlapped images are in register said second plurality of lines is displaced relative to said first plurality of lines by a fraction of the thickness of said lines, whereby misregister of said overlapped images in a first direction causes said first and second plurality of lines to overlap to a greater extent and misregister in an opposite direction causes said first and second plurality of lines to overlap to a lesser extent.

5. A method as set forth in claim 1, further comprising the steps of forming a third plurality of lines, similar to said first plurality of lines, in a third indicia area occupying another known position relative to said one of said overlapping images and forming a fourth plurality of lines, similar to said second plurality of lines, in a fourth indicia area occupying another known position relative to said other of said overlapping images, wherein said other known positions of said third and fourth indicia areas relative to said overlapped images are selected such that said third and fourth pluralities of lines overlap one another to a different extent than said first and second pluralities of lines.

6. A method as set forth in claim 5, wherein said step of detecting comprises the step of detecting the extent of overlap of said lines of said first and second indicia areas and providing a first value in accordance therewith and detecting the extent of overlap of said lines of said third and fourth indicia areas and providing a second value which varies in accordance therewith, and wherein said step of utilizing comprises the steps of determining the ratio of the sum of said first and second values to the difference of said values, and determining from said ratio the extent of misregister of said overlapping images.

7. A method as set forth in claim 5, wherein one of said steps of forming said third and fourth pluralities of lines includes the step of forming said lines such that the position of said third plurality of lines is displaced relative to said fourth plurality or lines by one quarter the period of said lines from the relative position of said first and second pluralities.

8. A method as set forth in claim 1, wherein said step of detecting comprises the steps of illuminating said first and second register indicia areas and detecting the amount of light reflected from the area in which said first and second indicia areas overlap, said detected amount of reflected light indicating the extent of overlap of said lines of said first and second indicia areas.

9. A method as set forth in claim 8, wherein said step of detecting the extent of overlap further comprises the steps of determining an offset value representing the amount of light which will be reflected when the lines of said first and second register indicia areas are interlaced, and correcting said detected amount of reflected light in accordance with said offset value.

10. A method as set forth in claim 9, wherein said step of correcting comprises the step of subtracting said offset value from said amount of reflected light so as to provide a difference indication which is proportional to the extent of overlap of said lines.

11. A method as set forth in claim 9, wherein said step of determining said offset value comprises the steps of determining the amount of light reflected from an area formed in a solid color corresponding to the color of said first lines, determining the amount of light reflected from an area formed in a solid color corresponding to the color of said second lines, and averaging the amounts determined in the preceding two determining steps so as to thereby provide an average indication corresponding to said offset value.

12. Apparatus for detecting misregister of colors in a multicolor image wherein the measure of a characteristic of a register indicia area is functionally dependent upon the extent of misregister of said colors in a predetermined direction, comprising:
means for sensing the measure of said characteristic of said register indicia area over at least a portion of said area and providing a signal indicative thereof, and means responsive to said signal indicative of said measure of said characteristic for determining therefrom the extent of misregister of said colors in said predetermined direction.

13. Apparatus as set forth in claim 12 wherein said characteristic is the reflectivity of said register indicia area, and wherein said means for sensing comprises means for sensing the reflectivity of said register indicia area.

14. Apparatus as set forth in claim 13, wherein said means for sensing the reflectivity of said register indicia area comprises means for illuminating said register indicia area, and means for sensing the amount of light reflected from said area and providing a signal having a value which varies therewith, said signal value thus indicating the measure of said characteristic in said register indicia area.

15. Apparatus as set forth in claim 12, wherein said means responsive to said signal indicative of said measure of said characteristic comprises a computer programmed to convert said signal indicative of said measure into a misregister correction signal for application to a misregistration correction device.

16. Apparatus as set forth in claim 15, wherein said computer is programmed with a function correlating said measure with register error.

17. Apparatus as set forth in claim 12 wherein said multicolor image is formed on a planar printing medium, and wherein said apparatus further comprises means positionable over said printing medium such that said sensing means is aligned above said register indicia area.

18. Apparatus as set forth in claims 12, wherein said multicolor image is formed on a moving web and wherein said apparatus further comprises means for mounting said sensing means over said moving web such that said sensing means is aligned at the transverse location on said moving web at which said register indicia area is formed.

19. Apparatus as set forth in claim 18, and further wherein said determining means includes means responsive to a trigger signal for sampling said signal provided by said sensing means, and further comprising means for providing said trigger signal when said register indicia area is passing said sensing means during movement of said web.

20. A method of determining the extent of misregister of colors in a multicolor image wherein the percentages of nonprint areas in first and second register indicia fields are each functionally dependent upon the extent of misregister of said colors in a predetermined direction, and wherein the percentages of nonprint area in said first and second fields change in different functional dependencies upon changes in the extent of misregister in said predetermined direction, comprising the steps of:
sensing the percentages of nonprint areas in each of said first and second fields, determining the ratio of the sum of said percentages to the difference of said percentages, and determining a said extent of misregister in said predetermined direction in accordance with the results of said ratio determining step.

21. A method as set forth in claim 20, wherein said sensing step comprises the steps of illuminating each of said first and second fields, and detecting the amount of reflected light from each said field when thus illuminated, said detected amount of reflected light being indicative of said percentages of nonprint areas.

22. A method as set forth in claim 21, wherein said sensing step also comprises the additional steps of determining the extent to which said detected amounts of reflected light are offset from being proportional to percentage of nonprint area, and correcting said detected amounts of reflected light in accordance with said offset so as to provide indications which are proportional to percentage of nonprint areas.

23. A method as set forth in claim 21, wherein said step of correcting comprises the step of subtracting the value of said offset from the value of each said amounts of reflected light so as to provide difference indications having values proportional to percentage of nonprint area.

24. A method of determining the extent of misregister of colors in a multicolor image having a register indicia area wherein the percentage of nonprint area is functionally dependent upon misregister of said colors in a predetermined direction, comprising the steps of:
illuminating said register indicia area, sensing the amount of light reflected from said area and providing a signal having a value which varies therewith, said value thus indicating the percentage of nonprint area in said register indicia area, and utilizing said value to calculate the extent of misregister of said colors in said predetermined direction.

25. Apparatus for determining the extent of misregister of colors in a multicolor image having a register indicia area wherein the reflectivity of said area is functionally dependent upon misregister of said colors in said predetermined direction, comprising:
means for illuminating said register indicia area;

means for sensing the intensity of light reflected from said area and for providing a signal having a value which varies in accordance therewith, said signal value thus indicating the reflectivity in said register indicia area, and means responsive to said signal for determining the extent of misregister in said predetermined direction in accordance with said signal value.

26. Apparatus as set forth in claim 25, wherein a second register indicia area is provided wherein the reflectivity of said area is functionally dependent upon misregister of said colors in said predetermined direction, said functional dependency being different than the functional dependency of said first register area, wherein said means for illuminating comprises means for illuminating each of said register indicia areas, wherein said means for sensing comprises means for sensing the intensity of light reflected from each of said register indicia areas and for providing corresponding signals in accordance therewith, and further wherein said means for determining the extent of misregister comprises means for determining the polarity and magnitude of misregister in said predetermined direction in accordance with the values of said corresponding signals.

27. Apparatus as set forth in claim 26, wherein said means for determining comprises means for determining the ratio of the difference of the values of said corresponding signals to the sum of the values of said corresponding signals, and for determining said polarity and magnitude of misregister in accordance with said ratio.

28. Apparatus as set forth in claim 25, wherein said register indicia area is formed as part of a color bar and wherein said apparatus further includes means for scanning said color bar with said means for illuminating and means for sensing.

29. Apparatus as set forth in claim 28, wherein said means for scanning said color bar comprises means for moving said means for illuminating and means for sensing along said color bar so that different portions of said color bar are sequentially illuminated and so that said sensing means provides at least one signal which sequentially assumes values representative of said sequentially illuminated portions of said color bar.

30. Apparatus as set forth in claim 25, wherein a second register indicia area is provided wherein the reflectivity of said second register indicia area is functionally dependent upon misregister of said colors in a second predetermined direction, wherein said means for illuminating comprises means for illuminating each of said register indicia areas, wherein means for sensing comprises means for sensing the intensity of light reflected from each of said register indicia areas and for providing corresponding signals in accordance therewith, and further wherein said means for determining the extent of misregister comprises means for determining the extent of misregister in each of first and second orthogonal directions in accordance with the values of said corresponding signals.

31. Apparatus as set forth in claim 25, wherein at least one additional area is provided whose reflectivity is indicative of the color density of at least one of said colors, wherein said means for illuminating includes means for illuminating said at least one additional area, wherein said means for sensing includes means for sensing the intensity of light reflected from said at least one additional area and for providing a signal indicative thereof and further wherein said means for determining comprises means for determining the extent of misregister in accordance with the values of the signals indicative of the intensity of relfected electromagnetic energy from said register indicia area and said additional area.

32. Apparatus as set forth in claim 31, wherein said register indicia area has two overlapping images formed therein in different colors, wherein two of said additional areas are provided, each having a solid image formed therein in a corresponding one of said different colors, wherein said means for illuminating and means for sensing respectively illuminate said areas and sense intensity of reflected light from each said additional area, and wherein said means for determining comprises means for averaging the values of signals provided by said sensing means for each additional area, and for utilizing the resulting average value to correct the value of said signal provided by said sensing means for said register indicia area.

33. Apparatus as set forth in claim 25, wherein said multicolor image is formed by a printing press having a lateral register direction representing said predetemined direction and wherein said determining means determines the extent of misregister in said lateral register direction in accordance with said signal value.

34. Apparatus as set forth in claim 25, wherein said multicolor image is formed by a rotary printing press having a circumferential register direction representing said predetermined direction, and wherein said determining means determines register direction in accordance with said signal value.

35. Apparatus as set forth in claim 25, wherein said multicolor image is formed by a rotary printing press having a circumferential register direction and has at least two register indicia areas formed thereon at different transverse locations, for each of which said predetermined direction corresponds to said circumferential register direction, wherein said illuminating means and sensing means respectively illuminate said areas and sense reflected light therefrom, and wherein said determining means determines skew of said colors relative to one another in accordance with differences in the values of the signals provided by said sensing means for each.

36. A method of determining the extent of misregister of two overlapping images, comprising the steps of:
forming a first register indicia in a known position relative to one of said two overlapping images, said first register indicia comprising plural straight, parallel lines, forming a second register indicia in a known position relative to the other of said two overlapping images, said second register indicia comprising plural straight, parallel lines which are also substantially parallel to the plural lines of said first register indicia, said known positions being selected such that said first and second register indicia overlap when said two overlapping images are in proper register, illuminating the area in which said first and second register indicia overlap, sensing the amount of light reflected from said illuminated area and providing an indication which varies in accordance therewith, and processing said indication to determine the extent of misregistration therefrom.

37. A method of determining misregistration between two overlapped printed images, said method comprising the steps of:
printing a first registration indicator in a first area at a known position relative to a first of said overlapped printed images, said first registration indicator including a first plurality of substantially parallel straight lines of predetermined width and transversely spaced apart from one another by a first predetermined dimension, printing a second registration indicator in a second area at a known position relative to a second of said two overlapped printed images, said second registration indicator including a second plurality of substantially parallel straight lines of predetermined width and transversely spaced apart from one another by a second predetermined dimension, said second plurality of lines at least partially overlapping said first plurality of lines, detecting the extent of overlap of said first and second plurality of lines by determining the amount of resultant printed or space area within said first and second areas, and utilizing said extent of overlap as a measure of misregistration of said two overlapping printed images.

38. The method set forth in claim 37 wherein the measure of misregistration is in a direction substantially perpendicular to said first and second plurality of lines.

39. The method set forth in claim 37 wherein said first registration indicator includes a third plurality of substantially parallel straight lines of predetermined width and transversely spaced apart from one another by a third predetermined dimension, said second registration indicator including a fourth plurality of substantially parallel straight lines of predetermined width and transversely spaced apart from one another by a fourth predetermined dimension, said fourth plurality of lines being substantially parallel to said third plurality of lines and at least partially overlapping said third plurality of lines, said fourth plurality of lines being transversely offset from said third plurality of lines by a pre-determined dimension, and further including the additional step of detecting the extent of resultant space between said first and second overlapping registration lines and the resultant space between said third and fourth overlapping registration lines, and utili-zing said extents as an indication of the direction of misregis-tration of said overlapping printed images.

40. Apparatus as set forth in claim 12, adapted for use in conjunction with a register indicia area having two similar over-lapping sets of parallel, straight lines, each set being formed in a different color, where in each set the spacing between the lines is comparable to the widths of the lines, and wherein said means for sensing comprises an optical detector for sensing light reflected from said area, said detector having a field of view which is broad enough that multiple ones of said lines of said overlapping sets of lines are within the field of view of said optical detector at one time, whereby the signal provided by said detector has a single value which is representative of the aver-age reflectivity of a portion of said area including multiple lines.