Image rendering system and associated method for minimizing contours in a quantized digital color image

Claim 1

A method for minimizing the contouring effects in a quantized digital image, comprising the steps of: a) quantizing an original image using a quantizer to produce a quantized image; b) determining, by a digital computer, the luminance value for each pixel of the original digital image and the quantized version of the original image; c) determining, by the computer, busy and smooth regions in the original digital image; d) for smooth regions, determining, by the computer, luminance variations (gradients) in the original digital image for each pixel by a first Sobel operator; e) for corresponding smooth regions, determining by the computer luminance variations in the quantized digital image for each pixel by a second Sobel operator; f) determining, by the computer, the difference between the original luminance variations and the quantized luminance variations for each pixel by a differencer coupled to said first Sobel operator and coupled to said second Sobel operator; g) selecting, by the computer, a threshold value that when exceeded is indicative of the existence of contours; h) comparing, by the computer, the difference of step f) with the threshold value of step g) and if the threshold is exceeded indexing the presence of a contour at an associated pixel of the quantized image; i) for each pixel (i,j) of the quantized image searching, by the computer, for a contour index in a window of pixels around each pixel; and j) when a contour index is found, computing a new color to be placed at each pixel (i,j).

Claim 2

A method for minimizing the contouring effects in a quantized digital image, comprising the steps of: a) quantizing an original image using a quantizer to produce a quantized image; b) determining, by a digital computer, the luminance value for each pixel of the original digital image and the quantized version of the original image; c) determining, by the computer, busy and smooth regions in the original digital image; d) for smooth regions, determining, by the computer, luminance variations (gradients) in the original digital image for each pixel by a first Sobel operator; e) for corresponding smooth regions, determining by the computer luminance variations in the quantized digital image for each pixel by a second Sobel operator; f) determining, by the computer, the difference between the original luminance variations and the quantized luminance variations for each pixel by a differencer coupled to said first Sobel operator and coupled to said second Sobel operator; g) selecting, by the computer, a threshold value that when exceeded is indicative of the existence of contours; h) comparing, by the computer, the difference of step f) with the threshold value of step g) and if the threshold is exceeded indexing the presence of a contour at an associated pixel of the quantized image; i) for each pixel (i,j) of the quantized image searching, by the computer, for a contour index in a window of pixels around each pixel; and j) when a contour index is found, computing a new color to be placed at each pixel (i,j).

Claim 3

A method for minimizing the contouring effects in a quantized digital color image, comprising the steps of: a) generating an original digital color image; b) quantizing the original digital color image using a quantizer to produce a quantized digital color image of said original digital color image; c) determining, by a digital computer, the luminance value for each color pixel of the original digital image and the quantized digital color image; d) determining, by the computer, busy and non-busy (smooth) regions of the original digital color image; e) for the smooth regions, determining, by the computer, the luminance variations (gradients) in the original digital color image for each pixel; f) for corresponding smooth regions, determining, by the computer, luminance variations in the quantized digital color image for each pixel; g) determining, by the computer, the difference between the original luminance variations and the quantized variations for each pixel of the smooth region; h) selecting, by the computer, a threshold value indicative of contours; i) comparing, by the computer, the difference of step g) with the selected threshold value of step h) and when the threshold is exceeded marking the presence of a contour at an associated pixel of the quantized digital color image; j) for each pixel (i,j) of the quantized digital color image, searching, by the computer, for a contour mark in a window of surrounding pixels; and k) when a contour mark is found, determining, by the computer, a new color to place at each pixel (i,j).

Claim 4

A method for minimizing the contouring effects in a quantized digital color image, comprising the steps of: a) generating an original digital color image; b) quantizing the original digital color image using a quantizer to produce a quantized digital color image of said original digital color image; c) determining, by a digital computer, the luminance value for each color pixel of the original digital image and the quantized digital color image; d) determining, by the computer, busy and non-busy (smooth) regions of the original digital color image; e) for the smooth regions, determining, by the computer, the luminance variations (gradients) in the original digital color image for each pixel; f) for corresponding smooth regions, determining, by the computer, luminance variations in the quantized digital color image for each pixel; g) determining, by the computer, the difference between the original luminance variations and the quantized variations for each pixel of the smooth region; h) selecting, by the computer, a threshold value indicative of contours; i) comparing, by the computer, the difference of step g) with the selected threshold value of step h) and when the threshold is exceeded marking the presence of a contour at an associated pixel of the quantized digital color image; j) for each pixel (i,j) of the quantized digital color image, searching, by the computer, for a contour mark in a window of surrounding pixels; and k) when a contour mark is found, determining, by the computer, a new color to place at each pixel (i,j).

Claim 10

A system for minimizing the contouring effects in a quantized digital image, comprising: a) a quantizer quantizing an original digital image; and b) a computer coupled to the quantizer, said computer comprising: means for determining a luminance value for each pixel of an original digital image and a quantized version of the original digital image; means for determining busy and smooth regions in the digital image; means for determining for smooth regions of the original digital image the luminance variations (gradients), said means for determining original image luminance variations including a first Sobel operator; means for determining the luminance variations in the quantized digital image for regions corresponding to the smooth regions of the original digital image for each pixel, said means for determining quantized image luminance variations including a second Sobel operator; means for determining a difference between the original luminance variations and the quantized luminance variations for each pixel of a smooth region, said means for determining the difference including a differencer coupled to said first Sobel operator and coupled to said second Sobel operator; means for establishing a threshold value that if exceeded is indicative of an existence of contours; means for receiving the difference and the threshold value and for comparing the difference with the threshold value and when the threshold is exceeded providing an index, reflecting a presence of a contour at an associated pixel of the quantized image; and search means for searching for a contour index in a window of pixels around each pixel (i,j) of said quantized image and for computing a new color to place at the pixel (i,j) if a contour index is found.

Claim 11

A system for minimizing the contouring effects in a quantized digital image, comprising: a) a quantizer quantizing an original digital image; and b) a computer coupled to the quantizer, said computer comprising: means for determining a luminance value for each pixel of an original digital image and a quantized version of the original digital image; means for determining busy and smooth regions in the digital image; means for determining for smooth regions of the original digital image the luminance variations (gradients), said means for determining original image luminance variations including a first Sobel operator; means for determining the luminance variations in the quantized digital image for regions corresponding to the smooth regions of the original digital image for each pixel, said means for determining quantized image luminance variations including a second Sobel operator; means for determining a difference between the original luminance variations and the quantized luminance variations for each pixel of a smooth region, said means for determining the difference including a differencer coupled to said first Sobel operator and coupled to said second Sobel operator; means for establishing a threshold value that if exceeded is indicative of an existence of contours; means for receiving the difference and the threshold value and for comparing the difference with the threshold value and when the threshold is exceeded providing an index, reflecting a presence of a contour at an associated pixel of the quantized image; and search means for searching for a contour index in a window of pixels around each pixel (i,j) of said quantized image and for computing a new color to place at the pixel (i,j) if a contour index is found.