Image analysis – Image enhancement or restoration – Artifact removal or suppression
Reexamination Certificate
1999-10-01
2001-04-10
Couso, Yon J. (Department: 2723)
Image analysis
Image enhancement or restoration
Artifact removal or suppression
C348S254000
Reexamination Certificate
active
06215913
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of image display systems, more particularly to methods and systems for reducing artifacts caused by quantization errors in digital display systems.
BACKGROUND OF THE INVENTION
Display systems create visual images from an electrical input image signal. Digital display systems, which use a quantized image signal, have many advantages when compared to the typical analog display system, including increased image rendition accuracy and the prospect of low-cost high-definition television implementation. However, without proper consideration for representation of the image's dynamic range, a digital system can induce new artifacts. Digital display systems can only display a finite number of intensity levels because the image data is quantized. Displaying an image using only a finite number intensity levels can detract from the overall image quality, causing visual artifacts such as false contouring or color shifting.
False contouring occurs when the quantization of an image display signal causes contours to appear in an output image that do not exist in the input image. For example, the image of a smooth ball has a gradual color or intensity gradient. When the analog input is quantized, the smooth image gradient may be transformed into several large blocks of adjacent pixels, wherein each pixel in a block is assigned an identical image signal value. If these large blocks of adjacent pixels are not separated by a region of non-homogenous pixels, the blocks will cause a “stair-step” effect and the smooth curve of the original image will appear to be a series of single-color flat surfaces.
Color shifting is a similar problem that occurs when the jumps in quantization levels do not occur at the same signal level for each color. For example, if the quantization levels are set so that the green component turns on first, followed by the red and blue components, a gray pixel will turn green, then yellow, before finally turning the desired gray. While color shifting is most evident when a pixel is initially turned on, as in the example above, higher intensity pixels may have perceptible changes in color as the three color signals individually increment.
False contouring and color shifting artifacts may be increased by either quantizing or digital processing processes including MPEG encoding or decoding, and the de-gamma processing. A solution to the false contouring and color shifting problem is needed that does not significantly increase the display system cost.
SUMMARY OF THE INVENTION
The present invention provides an improved method and apparatus for converting an input signal to an output signal representing the input signal. According to one embodiment of the present invention, a signal translation circuit is provided for converting an input signal into a digital output signal according to a translation function. The signal translation circuit is comprised of a first translation block for converting the input signal into a digital approximation representing the input signal. A second translation block accumulates an error signal representing the difference between the input signal and the digital approximation thereof. An adder receives the digital approximation from the first translation block and the error signal from the second translation block, and outputs an improved approximation signal representing the digital approximation and the error signal.
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Clatanoff Todd A.
Markandey Vishal
Marshall Stephen W.
Brady III Wade James
Brill Charles A.
Couso Yon J.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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