Television – Image signal processing circuitry specific to television – Transition or edge sharpeners
Reexamination Certificate
1999-09-22
2001-11-06
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Transition or edge sharpeners
C348S631000, C348S712000
Reexamination Certificate
active
06313883
ABSTRACT:
This invention relates to video signal processing and more particularly to processing color video signals so as to enhance the video images produced by such signals.
BACKGROUND OF THE INVENTION
The design of picture reproduction systems Involves consideration of a number of factors which affect how a picture is perceived by the human eye, including but not limited to the following factors: (1) sharpness or pictorial clarity, (2) contrast between light areas, dark areas and the related background illumination, and (3) realistic color values. In this context it should be noted that the eye does not respond equally to radiated energy of all visible wavelengths, there is a wide variation in response between observers, and the eye's response is a function of light intensity. See W. C. Hughes, “Electronic Engineers' Handbook”, 1st Ed., pp. 20-3, 20-4, McGraw-Hill 1975.
Color video (television) standards are based on the manner in which the eye perceives colored light. In color video systems a wide range of colors can be reproduced for reception by the eye by the addition of only three monochromatic light sources, red, green and blue. The color signals produced by a video camera are encoded before being transmitted to a television receiver or other video display device, the encoded signals comprising a luminance information signal and color signals. As explained by Hughes (supra), p.20-3, the luminance of a surface is the effect on the average eye of the light emitted by a unit area of the surface. Luminance is the integrated effect of the eye response and the visible light power radiated by the surface, both of which are functions of wavelength.
Spatial frequency is the frequency at which an image changes over distance. Luminance is more significant than color at higher spatial frequencies. The human eye response to high spatial frequency information is not the same as it is for low spatial frequency information. Accordingly efforts have been made to process spatial frequency video information signals for the purpose of enhancing the sharpness of reproduced video images. One such effort is represented by U.S. Pat. No. 4,721,998, issued Jan. 26, 1988 to W. E. Glenn for “Method And Apparatus For Processing Color Video Signals”. Other such efforts may be known to persons skilled in the art.
The idea of enhancing the images produced by a video camera is particularly intriguing in the case of producing images for surgical or medical purposes. For such purposes, video cameras are utilized in the form of video endoscopes, so-called because the camera is embodied as an integral part of the endoscope, or as an accessory that is attached to the back end of a conventional optical endoscope. In many surgical procedures it is often helpful to enhance color video images in a way which will add to the information perceived by the medical specialist. Details such as small or large blood vessels, differences in tissue condition or tissue types, and the margins between them can be made more distinct and informative by appropriately electronically enhancing the image reproduced by use of the video signals.
OBJECTS AND SUMMARY OF THE INVENTION
A primary object of the invention is to provide a novel method of processing video signals representative of an image so as to produce an enhanced reproduction of that image, or a portion thereof.
Still another object is to provide a method and apparatus for electronically processing video signals representing images of an object or scene so that details of some portion or all of said object or scene are enhanced in the video display reproduction of said images.
These and other objects are achieved by deriving one or more digital color-representative signals and a digital luminance signal from a suitable source, for example, a color video camera or a video recording system or from previously processed video signals. The digital luminance signal is passed through a low-pass FIR (finite impulse response) filter that removes the higher spatial frequency components. The resulting low pass digital data is subtracted from the original luminance image data, leaving the digital data representing the high-pass image components that were rejected by the low-pass filter. The high-pass digital data for each pixel is subjected to amplification (“boost”) according to a function of the low-pass data value at that pixel. Essentially the high frequency components of different pixels in an image are boosted differently according to the low spatial frequency components of the same pixels. The lower the value of the lower spatial frequency components, the more the higher spatial frequency components get boosted. The low-pass data and the selectively boosted high-pass data are subsequently added together to form the finite local enhancement version of the luminance data. The finite local enhanced luminance data is used to generate a display of the observed image with all or part of the displayed image being enhanced. To maximize the benefit of the enhancement process, at each pixel the enhanced values of luminance are compared against predetermine minimum and maximum values allowed for image data. Values beyond the valid range are set equal to the predetermined minimum or maximum values respectively.
The invention enables different degrees of enhancement of the light and dark areas of the image, with the darker parts of the picture getting more boost than the lighter areas, unless the operator deliberately selects some other result. The operator may interface with the boost table by selecting a region of the image to be enhanced, and/or by selecting a profile of boost values (less and/or greater than unity) to produce a desired enhancement result.
REFERENCES:
patent: 4400721 (1983-08-01), Macovski
patent: 4721998 (1988-01-01), Glenn
patent: 4868645 (1989-09-01), Kobayashi
patent: 5012331 (1991-04-01), Schuster
patent: 5053865 (1991-10-01), Ubukata
patent: 5891015 (1999-04-01), Strahle
W.C. Hughes, “Electronic Engineers' Handbook”, 1st Ed., pp. 20-3, 20-4, McGraw-Hill 1975.
Hsia Sherrie
Pandiscio & Pandiscio
Vista Medical Technologies, Inc.
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