Method and apparatus for image manipulation via a dither matrix
AssigneeSilverbrook Research Pty Ltd
InventorsRichard Thomas Plunkett, Simon Robert Walmsley, Kia Silverbrook, Raul Evelio Vera
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Abstract
Efficiently processing contone image data by determining one or more characteristics of the image data and using these characteristics to manipulate the dither matrix so that the printed image is enhanced.
Claims9
A method of operating a micro-processor to manipulate a contone image data to be halftoned with a dither matrix, the contone image data having colour level values for pixels in the image, the colour level values having a certain distribution within a predetermined range of discrete colour levels, the method comprising:
- deriving a secondary dither matrix from a predetermined primary dither matrix, the primary dither matrix having a range of threshold values and the secondary dither matrix has a compressed range of threshold values, the compressed range of threshold values being determined in accordance with the following algorithm:
- Tnew=Lmin+Told·(Lmax−Lmin)/Ltotal
- where:
- Lmax is the maximum number of discrete colour levels if a predetermined top-most portion of the colour level values of the contone image data is disregarded;
- Lmin is the minimum number of discrete colour levels that contain a predetermined bottom-most number of the colour level values of the contone image data;
- Ltotal is the total number of levels in the range of discrete colour levels;
- Tnew is the compressed threshold values in the secondary dither matrix;
- and,
- Told is the threshold value in the primary dither matrix;
- and,
- halftoning the contone image data with the secondary dither matrix.
A print engine controller for an inkjet printer, the print engine controller comprising:
- a processor for receiving contone image data, the contone image data having colour level values for pixels in the image;
- memory storing a predetermined primary dither matrix, the primary dither matrix having a range of threshold values;
- wherein,
- the processor is configured to determine at least one characteristic of the contone image data and derive a secondary dither matrix, the secondary dither matrix has a compressed range of threshold values for comparison to the colour level values of the contone image data during halftoning;
- such that,
- the contone image data is halftoned with the secondary dither matrix prior to printing;
- wherein the threshold values in the compressed range in the secondary matrix are determined in accordance with the following algorithm:
- Tnew=Lmin+Told·(Lmax−Lmin)/Ltotal
- where:
- Tnew is the compressed threshold values in the secondary dither matrix;
- Told is the threshold value in the primary dither matrix;
- Lmax is the maximum number of discrete colour levels if a top-most portion of the colour level values of the contone image data is disregarded;
- Lmin is the minimum number of discrete colour levels that contain a bottom-most number of the colour level values of the contone image data;
- and,
- Ltotal is the total number of levels in the range of discrete colour levels.
Dependencies are inferred from the claim text.