Halftoning with color error diffusion of one separation based on color error diffusion of a previous separation

A method comprising:

• halftoning a source image, the halftoning including error diffusion processing of a first separation of the plural color separations of a pre-rendered image after error diffusion processing a second separation of the plural color separations of the pre-rendered image, the error diffusion processing of the first separation comprising, for respective pixel values corresponding to the first separation, choosing respective magnitudes of the respective pixel values as a function of the error diffusion processing of the second separation;
• outputting a rendered image including the same plural color separations, the output rendered image being populated with, for the first separation, pixel information based on the respective magnitudes;
• and
• printing or displaying the output for each color separation to produce a halftoned image;
• wherein error diffusion processing is performed on each of the plural color separations in a given sequential order, and wherein the outputting of the rendered image comprises, for each output color separation, selecting image dots or pixels as active if a modified input for the image dot or pixel is greater than a particular threshold determined as a function of an error value associated with a corresponding dot or pixel in a previously processed color separation, and selecting image dots or pixels as inactive otherwise;
• and
• wherein the outputting of the rendered image includes outputting, for each color separation, for each pixel or dot within a given color separation k, a “1” when a modified input for the same pixel or dot is greater than 0.5 minus the sum of the products of an impact parameter times an error value for each of the previously processed color separations.

A machine-readable medium comprising encoded information, the encoded information, when operably interacting with the machine, causing:

• halftoning of a source image, thereby converting multiple-level pixel input values, of each of plural color separations of a pre-rendered image, to binary output pixel values, the halftoning including error diffusion processing of a first separation of the plural color separations of the pre-rendered image after error diffusion processing a second separation of the plural color separations of the pre-rendered image, the error diffusion processing of the first separation including, for respective ones of the multiple-level input pixel values of the first separation, corresponding binary output pixel values as a function of the error diffusion processing of the second separation;
• outputting of a rendered image comprising the same plural color separations, the output rendered image being populated with, for the first separation, pixel information based on the respective magnitudes;
• and
• performing error diffusion processing on each of the plural color separations in a given sequential order, wherein the outputting of the rendered image includes, for each output color separation, selecting image dots or pixels as active if a modified input for the image dot or pixel is greater than a particular threshold determined as a function of an error value associated with a corresponding dot or pixel in a previously processed color separation, and selecting image dots or pixels as inactive otherwise, the error value being calculated by determining a difference between an output of the previously processed color separation and a modified input of the previously processed color separation.

Apparatus comprising:

• a color separation processor to separate a source image having a given color scheme into color separations of a different color scheme;
• an error diffusion engine;
• a controller to control the error diffusion engine to halftone a source image, thereby converting multiple-level pixel input values, of each of plural color separations of a pre-rendered image, to binary output pixel values, the halftoning including error diffusion processing of a first separation of the plural color separations of the pre-rendered image after error diffusion processing a second separation of the plural color separations of the pre-rendered image, the error diffusion processing of the first separation including, for respective ones of the multiple-level input pixel values of the first separation, corresponding binary output pixel values as a function of the error diffusion processing of the second separation;
• and
• rendering circuitry to output a rendered image including the same plural color separations, the output rendered image being populated with, for the first separation, pixel information based on the respective magnitudes;
• wherein the error diffusion processing is controlled by the controller to be performed on each of the plural color separations in a given sequential order, and wherein the output of the rendered image comprises, for each output color separation, selecting image dots or pixels as active if a modified input for the image dot or pixel is greater than a particular threshold determined as a function of an error value associated with a corresponding dot or pixel in a previously processed color separation, and selecting image dots or pixels as inactive otherwise, the error value being calculated by determining a difference between an output of the previously processed color separation and a modified input of the previously processed color separation.