Computer graphics processing and selective visual display system – Display peripheral interface input device
Reexamination Certificate
1997-04-23
2001-01-30
Shankar, Vijay (Department: 2778)
Computer graphics processing and selective visual display system
Display peripheral interface input device
C348S557000
Reexamination Certificate
active
06181321
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computerized color image processing of digital color images, and more particularly to systems and techniques for automatic contrast enhancement, automatic color cast removal with contrast enhancement, and combined color cast removal and contrast enhancement where a user can adjust a single control for maximum color cast removal, maximum contrast enhancement, or any intermediate position.
2. Description of the Related Art
In many instances an original color image will include an undesirable color cast or tint. For example, as photographs age they often acquire a yellow cast. In addition, color casts may arise from a variety of circumstances, including the type of lighting or the quality/color sensitivity of photographic film used when taking a photograph.
Conventional techniques have been employed in order to reduce or eliminate color casts in original color images. However, in order to achieve good results, it has generally been necessary to have significant user input. This can be inconvenient in many instances, and can also lead to less than optimal results.
For example, in one conventional technique the user is required to identify the white point in the image, and then the image colors are adjusted accordingly. However, with such a technique, different users might disagree about which point in the image is the white point. Accordingly, the image processing parameters will generally be based upon a subjective determination, which might not always be desirable. Moreover, a user's determination of the white point might be skewed based on the color makeup of the image. For example, a point might erroneously appear to be the white point only because surrounding colors interfere with the user's perception of the point's true color. Finally, selecting the white point in each image can be very tedious and burdensome, particularly when many images are to be processed, and generally will be impractical if one wishes to process frame images on a real time basis.
Another common defect of color images is poor contrast. This problem can obscure image information, as well as negatively affect the general appearance of the image. Although conventional techniques exist for enhancing contrast, such conventional techniques generally do not provide optimal results in many situations. For example, many conventional contrast enhancement techniques do not provide acceptable results when the original image has both very dark and very bright pixels.
Moreover, it is often desirable to allow a user to have some control over the amount of contrast enhancement and color cast removal performed on the original image. For instance, a fully automatic color cast removal technique probably will be incapable of determining when a user subjectively wants the image to have a color cast, such as when a user has taken a photograph through a colored filter or when a user intentionally wishes to mimic an old and yellowed photograph. Similarly, a user might, for aesthetic reasons, want to vary the amount of color contrast in an image. Conventionally, however, in order to permit a user to adjust both the amount of contrast enhancement and the degree of color cast removal, at least two controls have been provided (one for color cast removal and one for contrast enhancement). Accordingly, simultaneous adjustment of both color cast removal and contrast enhancement using conventional techniques has not heretofore been possible.
SUMMARY OF THE INVENTION
The present invention addresses these problems by providing techniques for automatic color cast removal, automatic contrast enhancement, and combined color cast removal and contrast enhancement where a user can adjust a single control for maximum color cast removal, maximum contrast enhancement, or any intermediate position.
In one embodiment of the invention, an original image is digitally processed so as to automatically enhance color contrast in the original image. According to this embodiment, the original image is designated as highkey only if, for each color component in the original image, there exists a sufficient percentage of pixels having a pixel intensity level for that color component which is greater than or equal to a first threshold intensity value. The original image is designated as lowkey only if, for each color component in the original image, there exists a sufficient percentage of pixels having a pixel intensity level for that color component which is less than or equal to a second threshold intensity value. A first mapping is performed for each color component of the original image if the original image is not both highkey and lowkey, and a second mapping is performed, for each color component of the original image if the original image is both highkey and lowkey. The second mapping, which is different than the first mapping, enhances contrast for a range of the brightest pixels and a range of the darkest pixels and reduces contrast for pixels having an intensity between the ranges of darkest and brightest pixels for which contrast is enhanced.
By virtue of this arrangement, contrast enhancement is provided automatically and without user input. Moreover, the foregoing arrangement is designed to specifically address the situation where an original image contains both very dark and very bright pixels. Accordingly, the foregoing embodiment can provide good results in situations where conventional systems typically fail.
In a further embodiment, an original image is digitally processed so as to automatically remove color cast from the original image. According to this embodiment, pixel intensity levels for each color component i in an original image are obtained. The pixel intensity levels for each color component i are separately mapped to new pixel intensity levels for that color component by (a) determining a value d
i
′ based on the darkest d
i
percent of pixels, (b) mapping pixels darker than d
i
′ to a small first range of dark intensity levels, (c) determining a value b
i
′ based on the brightest b
i
percent of pixels, (d) mapping pixels brighter than b
i
′ to a small second range of bright intensity levels, and (e) mapping the remainder of the pixels to fall between the first and second ranges, where d
i
and b
i
are numbers pre-selected for each color component i. Finally, a new image is created using the new pixel intensity levels for each of the color components.
The foregoing arrangement thus provides for fully automatic color cast removal and can provide good results under a variety of circumstances without any user input. For example, the foregoing embodiment can provide good results without the necessity of requiring the user to designate a white point.
In a further embodiment, an original image is digitally processed while permitting a user to control an amount of color cast removal and an amount of color contrast enhancement performed on the original image. According to this embodiment, a user interface, which includes a control element having a single degree of freedom, is provided. The original image is digitally processed. User adjustment of the control element is responded to by simultaneously varying the degree of color cast removal and the amount of color contrast enhancement performed on the original image during the digital processing.
By virtue of this arrangement, a user can easily and without significant training or experience simultaneously adjust the amount of contrast enhancement and the degree of color cast removal performed on an original image. Moreover, these adjustments can be made with a single control, and generally without the necessity of significant user action, such as locating a white point.
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patent: 4984071 (1991-01-01), Yonezawa
patent: 5172224 (1992-12-01), Collette et al.
patent: 5201027 (1993-04-01), Casini
patent: 5245417 (1993-09-01), Hibi et al.
patent: 5265200 (1993-11-01), Edgar
patent: 5335097 (1994-08-01), Murakami
paten
Hui Jonathan
Kohler Timothy L.
Zhao Jun
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Frenel Vanel
Shankar Vijay
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