Method for halftoning a multi-channel digital color image having at least one group of similar color channels

A method for halftoning a multi-channel digital color image having an x,y array of color pixel values, wherein at least two color channels are similar having substantially the same color but with low- and high-densities, said method comprising:

• providing a set of dither matrices including:
• a) a matrix of dither values for each group of similar color channels wherein two or more of the matrices of dither values are designed jointly to minimize a visual cost function;
• and
• b) for at least one group of similar color channels, an inverted matrix of dither values formed by subtracting the value of each element of the matrix of dither values for that group from a predetermined maximum value, the inverted matrix of dither values being associated with one of the low- or high-density color channels, and the matrix of dither values for that group being associated with the other low- or high-density color channel.

A method for halftoning a multi-channel digital color image having an x,y array of color pixel values, wherein at least two of the color channels are similar having substantially the same color but with low- and high-densities, comprising the steps of:

• a) providing a set of dither bitmaps for each group of similar color channels wherein the dither bitmaps for at least two of the groups of similar color channels are designed jointly to minimize a visual cost function;
• b) for at least one group of similar color channels, forming an inverted set of dither bitmaps by subtracting the value of each element of the dither bitmaps for that group from a predetermined maximum value, associating the inverted set of dither bitmaps with one of the low- or high-density color channels, and associating the set of dither bitmaps for that group with the other low- or high-density color channel;
• c) for each color channel of the multi-channel digital color image, selecting the dither bitmap from the set of dither bitmaps associated with that color channel corresponding to the pixel value for a pixel in the multi-channel digital color image;
• d) for each color channel modularly addressing the selected dither bitmap with the location of the pixel to obtain an output halftone image value;
• and
• e) repeating steps c) and d) for each pixel in the multi-channel digital color image.

A method for halftoning a multi-channel digital color image having an x,y array of color pixel values, wherein at least two color channels are similar having substantially the same color but with low- and high-densities, comprising:

• providing a set of dither bitmaps including:
• a) a set of dither bitmaps for each group of similar color channels wherein two or more of the sets of dither bitmaps are designed jointly to minimize a visual cost function;
• and
• b) for at least one group of similar color channels, an inverted set of dither bitmaps formed by subtracting the value of each element of the dither bitmaps for that group from a predetermined maximum value, the inverted set of dither bitmaps being associated with one of the low- or high-density color channels, and the set of dither bitmaps for that group being associated with the other low- or high-density color channel.

A method for halftoning a multi-channel digital color image having an x,y array of color pixel values, wherein at least two of the color channels are similar having substantially the same color but with low- and high-densities, comprising the steps of:

• a) providing a set of first bitmaps for each group of similar color channels;
• b) for at least one group of similar color channels, forming an inverted set of second bitmaps by subtracting the value of each element of the first bitmaps for that group from a predetermined maximum value, associating the inverted set of second bitmaps with one of the low- or high-density color channels, and associating the set of first bitmaps for that group with the other low- or high-density color channel;
• c) for each color channel of the multi-channel digital color image, selecting the bitmap from the set associated with that color channel corresponding to the pixel value for a pixel in the multi-channel digital color image;
• d) for each color channel modularly addressing the selected bitmap with the location of the pixel to obtain an output halftone image value;
• and
• e) repeating steps c) and d) for each pixel in the multi-channel digital color image.

A method for halftoning a multi-channel digital color image having an x,y array of color pixel values, wherein at least two color channels are similar having substantially the same color but with low- and high-densities, comprising:

• providing a set of dither bitmaps including:
• a) a set of dither bitmaps for each group of similar color channels;
• and
• b) for at least one group of similar color channels, an inverted set of dither bitmaps formed by subtracting the value of each element of the dither bitmaps for that group from a predetermined maximum value, the inverted set of dither bitmaps being associated with one of the low- or high-density color channels, and the set of dither bitmaps for that group being associated with the other low- or high-density color channel.

A method for halftoning a multi-channel digital color image having an x,y array of color pixel values, wherein at least two color channels are similar having substantially the same color but with low- and high-densities, comprising:

• providing a set of bitmaps including:
• a) a set of first bitmaps for each group of similar color channels;
• and
• b) for at least one group of similar color channels, an inverted set of second bitmaps formed by subtracting the value of each element of the first bitmaps for that group from a predetermined maximum value, the inverted set of second bitmaps being associated with one of the low- or high-density color channels, and the set of first bitmaps for that group being associated with the other low- or high-density color channel.