Pattern dithering

A method of generating from a source image a target image comprising target pixels having colors limited to colors found in a target palette, the method comprising:

• determining a source color of a region of the source image corresponding to a location of a target pixel;
• generating two or more temporary colors in the vicinity of the source color;
• computing a candidate color for each temporary color, where each candidate color is a color in the target palette closest to the respective temporary color;
• sorting the candidate colors;
• and
• selecting one candidate color for a target color of the target pixel based on the position of the target pixel in the target image.

A method of generating from a source image a target image comprising target pixels having colors limited to colors found in a target palette, the method comprising:

• determining a source color of a region of the source image corresponding to a location of a target pixel;
• evaluating a function to calculate an integer value n in a range of integers 1 to N;
• using the source color to compute a sequence of N candidate colors, where each candidate color is a color in the target palette;
• and
• setting a target color of the target pixel to be the nth candidate color in the sequence of N candidate colors.

A method of generating from a source image a target image comprising target pixels having colors limited to colors found in a target palette, the method comprising:

• determining a source color of a region of the source image corresponding to a location of a target pixel;
• generating two or more candidate colors for a target color of the target pixel from the source color, where the candidate colors are colors in the target palette, where any target palette color can occur more than once among the candidate colors, and where candidate colors are generated to have an average color close to the source color;
• determining a luminance value for each candidate color;
• applying a dither ordering function to select one candidate color from the two or more candidate colors, the dither ordering function operating to spread out luminance differences so that in any local area, overly bright pixels tend to be near overly dark pixels;
• and
• setting the target color of the target pixel to be the selected candidate color.

A system for generating a target image of target pixels having a target palette from a source image, comprising:

• means for determining a source color based on a location of a target pixel;
• means for generating two or more candidate colors for a target color of the target pixel from the source color, where the candidate colors are colors in the target palette;
• means for selecting one candidate color;
• and
• means for setting a target color of the target pixel to be the selected candidate color.

A computer program product stored on a computer-readable medium, for generating a target image of target pixels having a target palette from a source image, the computer program comprising instructions operable to cause a computer to:

• determine a source color of a region of the source image corresponding to a location of a target pixel;
• generate two or more candidate colors for a target color of the target pixel from the source color, where the candidate colors are colors in the target palette;
• select one candidate color;
• and
• set the target color of the target pixel to be the selected candidate color.

A computer program product stored on a computer-readable medium, for generating from a source image a target image comprising target pixels having colors limited to colors found in a target palette, the computer program product comprising instructions operable to cause a computer to:

• determine a source color of a region of the source image corresponding to a location of a target pixel;
• evaluate a function to calculate an integer value n in a range of integers 1 to N;
• use the source color to compute a sequence of N candidate colors, where each candidate color is a color in the target palette;
• and
• set a target color of the target pixel to be the n'th candidate color in the sequence of N candidate colors.

A computer program product stored on a computer-readable medium, for generating from a source image a target image comprising target pixels having colors limited to colors found in a target palette, the computer program product comprising instructions operable to cause a computer to:

• determine a source color of a region of the source image corresponding to a location of a target pixel;
• generate two or more candidate colors for a target color of the target pixel from the source color, where the candidate colors are colors in the target palette, where any target palette color can occur more than once among the candidate colors, and where candidate colors are generated to have an average color close to the source color;
• determine a luminance value for each candidate color;
• apply a dither ordering function to select one candidate color from the two or more candidate colors, the dither ordering function operating to spread out luminance differences so that in any local area, overly bright pixels tend to be near overly dark pixels;
• and
• set the target color of the target pixel to be the selected candidate color.