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United States Patent m
[li] 4,156,914  May 29, 1979
 COMPUTER IMAGE DISPLAY SYSTEM AND PROCESSOR THEREFOR
 Inventor: William E. Westell, Weston, Mass.
 Assignee: Baird Corporation, Bedford, Mass.
 Appl. No.: 825,693
 Filed: Aug. 18,1977
 Int. C1.2 G06J 1/00; G06G 7/19
 U.S. CI 364/515; 358/903;
364/518; 364/604; 364/825
 Field of Search 364/514, 515, 518, 521,
364/604, 724, 728, 819, 822, 825; 350/162 SF;
 References Cited
U.S. PATENT DOCUMENTS
3,337,870 8/1967 Allen et al 364/819 X
3,809,873 5/1974 Klahr 364/822
3,971,921 7/1976 Schmit et al 364/822 X
4,025,772 5/1977 Constant 364/728
OTHER PUBLICATIONS Crooker et al. "Measurement of Optical Autocorrela
tion Functions Using a Signal Averager" Rev. of Sci. Instrum., vol. 47, No. 5, May 1976.
Primary Examiner—Joseph F. Ruggiero
Attorney, Agent, or Firm—Morse, Altman, Oates &
A computer image display system in which digital sampled data, generated by an image transducer and processed by a computer, is convolved with a Gaussian function in a display processor in order to produce a continuous analog image presentation on a diplay. First, the Gaussian function is convolved vertically with computer stored intensities in a vertical slice of interest, that is, multiplied by those intensity values in the vertical slice and summed to derive a resultant intermediate value on a given horizontal line. Then, the Gaussian function is convolved with the resultant intermediate value on a given horizontal line in order to derive final values which are to be displayed.
13 Claims, 6 Drawing Figures
U.S. Patent May 29, 1979 Sheet 1 of 2 4,156,914
U.S. Patent May 29, 1979 Sheet 2 of 2 4,156,914
COMPUTER IMAGE DISPLAY SYSTEM AND
BACKGROUND OF THE INVENTION 5
1. Field of the Invention
The present invention relates to display systems and, more particularly, is directed towards computer displays, TV displays, digital image processing, radiographic instrumentation, two-dimensional spatial 10 matched filtering, sampled-data reconstruction (interpolation and smoothing), optical image processing, solid-state imaging array display and low-bandwidth TV picture transmission and reception.
2. Description of the Prior Art 15 Two-dimensional images that have been spatiallysampled, for example in computer processing, generate display artifacts due to aliasing, leakage and data quantization if the digital image data is simply converted to analog intensity values and is displayed directly. These 20 artifacts seriously degrade the quality of image perception. The well-known electrical communication theory solution to minimize display artifacts includes the use of
a sharp cut-off low-pass filter having a sin x/x weighting function (impulse response) with zeroes 25 matched to the sampling intervals. In addition, an aliasing filter is employed before sampling to satisfy the band-limiting requirements (Nyquist Limit) of the classical sampling theorem.
However, implementation of this theoretically- 30 optimum technique for sampled-data reconstruction, interpolation and smoothing is often impractical even for one-dimensional data because (1) the sin x/x response requires a very high order filter (many poles) to merely approximate the theoretical optimum, and (2) 35 the sin x/x time response must be maintained precisely matched to the sampling rate to avoid spurious artifacts (aliasing or moire effects). Two-dimensional implementation is even more impractical because of complexity and criticality of matching; with serious artifact genera- 40 tion resulting from only slight mismatching. Practical approximations to the ideal filter generate artifacts which are particularly noticeable when the image is moved, especially when the image is rotated.
SUMMARY OF THE INVENTION 45
It is an object of the present invention to provide a computer image display system and processor which does not suffer from the heretofor mentioned disadvantages and limitations. 50
Another object of the present invention is to provide a computer image display system and processor employing non-critical and practical techniques.
A futher object of the present invention is to provide an optical matched filter for optimization of image per- 55 ception by minimizing display noise.
A still further object of the invention is to provide a computer image display system in which digital sampled data, generated by an image transducer and processed by a computer, is convolved with a Gaussian 60 function in a display processor in order to produce a continuous analog image presentation on a display. The processor includes a two-dimensional Gaussian interpolation filter. The Gaussian function provides data smoothing having rotational symmetry of the final dis- 65 play response. The processing can be performed by simple sequential operation on X and Y coordinate data. The equivalent one-dimensional Gaussian function is
first convolved vertically with computer stored intensities in a vertical slice of interest. That is, Gaussian function is multiplied by intensity values in the vertical slice and summed to derive resultant intermediate values at each point on a given horizontal line. The same equivalent one-dimensional Gaussian function is then convolved with these resultant intermediate values on a given horizontal line in order to derive final values which are to be displayed.
Other objects of the present invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the methods and systems, together with their steps, parts, elements and interrelationships that are exemplified in the following disclosure, the scope of which will be indicated in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
A fuller understanding of the nature and objects of the present invention will become apparent upon consideration of the following detailed description taken in connection with the accompanying drawings, wherein:
FIG. 1 is a block diagram of a digital image-processor and display system embodying the present invention;
FIG. 2 is a block diagram of a digital communications link embodying the present invention;
FIG. 3 is a block diagram of a computer imageprocessor and display system embodying the present invention;
FIG. 4A is a block and schematic diagram of the image-processor embodying the present invention;
FIG. 4B is a schematic diagram illustrating vertical convolution principles of the invention; and
FIG. 4C is a schematic diagram illustrating horizontal convolution principles of the invention.
DETAILED DESCRIPTION OF THE
Referring now to the drawings, particularly FIG. 1, there is shown a digital image-processor and display system 20 for computer processing and display of signals generated by an image transducer 22, for example a camera, such as a TV camera, a solid state camera, an infrared camera or a gamma-camera. Image transducer 22 includes an imager such as a lens or collimator and an image sensor such as an image dissector, an image orthicon, a vidicon, a solid state array such as a charge-coupled device, a charge-injection device, silicon-diode or infrared-detector array, or a multi-crystal photomultiplier array of the type used in a gamma camera. The signals generated by transducer 22 are processed in an image processor 24 which generates digital data representation of the sensed image. Image processor 24 is operative to correct diffidences and/or limitations of transducer 22, for example, corrects for improper responses, image distortion, non-uniformity of the response, etc. The digital data generated by image processor 24 is applied to a display processor 26 which includes a two-dimensional Gaussian interpolation filter 27 that convolves the digital data with the Gaussian function for continuous analog image presentation on a display 28, for example, a cathode-ray tube television monitor. As hereinafter described in connection with the detailed description of processor 26, the Gaussian function is first convolved vertically with computer stored intensities in a vertical slice of interest, that is, multiplied by those intensity values ill the vertical slice and summed to derive resultant intermediate values at