Method of processing a digital image by means of ordered dithering technique description
AssigneeSTMicroelectronics S.r.l.
InventorsPier Luigi Gardella, Massimiliano Barone, Gary Sweet, Danilo Pau, Stephen Hill, Simon Goda
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Abstract
A dither matrix is applied to a high-resolution image to compare the value of each of the pixels that compose it with a threshold value of the matrix and to obtain an output value of the matrix (Dither matrix value) from each comparison. To each pixel value of the image there is applied an algorithm involving simple but displacement operation, namely shifts to the left and shifts to the right. The pixel values of a low-resolution image are output from the applied algorithm.
Claims20
An ordered dithering method for processing a starting image having a first chromatic resolution and formed by N×M pixels, for obtaining an output image having a second chromatic resolution, said second resolution being lower than said first chromatic resolution, said starting image being suitable for being decomposed in three color channels, respectively R (red), B (blue) and G (green), and a brightness channel (A), said method comprising the steps of:
- predisposing a first and a second dither matrix, each of said matrices comprising a multiplicity of threshold values ordered in j rows and j columns, where j is smaller than both N and M,
- repeatedly applying the first dither matrix to the R, B and A channels of the starting image and the second dither matrix to the G channel of the starting image for comparing the value of each of the pixels that compose said channels with a selected respective threshold value belonging to the respective dither matrix;
- wherein said first and second dither matrices comprise the same threshold values, said threshold values being arranged differently within said two matrices.
A method for processing a starting image having a first chromatic resolution and formed by NxM pixels to generate an output image having a second chromatic resolution, the second chromatic resolution being lower than said first chromatic resolution, the method comprising:
- generating a first dither matrix including a plurality of threshold values;
- generating a second dither matrix including the plurality of threshold values, the plurality of threshold values being arranged differently within the second dither matrix than within the first dither matrix, and arranged such that the second dither matrix is not the additive inverse of the first dither matrix;
- repeatedly applying the first dither matrix to selected groups of pixels in the starting image by comparing a value of each of the pixels in the group to a corresponding threshold value in the first dither matrix, wherein the application of the matrix to each selected group of pixels generates corresponding groups of pixels in the output image;
- and
- repeatedly applying the second dither matrix to at least one selected group of pixels in the starting image by comparing a value of each of the pixels in the group to a corresponding threshold value in the second dither matrix, wherein the application of the matrix to each selected group of pixels generates corresponding groups of pixels in the output image.
A method for processing a starting image having a first chromatic resolution and formed by N×M pixels to generate an output image having a second chromatic resolution, the second chromatic resolution being lower than said first chromatic resolution, the method comprising:
- generating a first dither matrix including a plurality of first threshold values;
- generating a second dither matrix including a plurality of second threshold values, the second threshold values being the same as the first threshold values but the second threshold values being arranged differently within the second dither matrix than the first threshold values are arranged within the first dither matrix;
- repeatedly applying the first dither matrix to selected groups of pixels in the starting image by comparing a value of each of the pixels in the group to a corresponding threshold value in the first dither matrix, wherein the application of the matrix to each selected group of pixels generates corresponding groups of pixels in the output image;
- and
- repeatedly applying the second dither matrix to at least one selected group of pixels in the starting image by comparing a value of each of the pixels in the group to a corresponding threshold value in the second dither matrix, wherein the application of the matrix to each selected group of pixels generates corresponding groups of pixels in the output image;
- wherein the first dither matrix is applied to red, blue, and luminosity groups of pixels in the starting image and wherein the second dither matrix is applied to green pixels in the starting image.
A computer-readable medium storing a dither matrix data structure for application to digital image data, the dither matrix data structure comprising:
- a table including sets of X and Y values, each set of X and Y values pointing to an associated threshold value given by the formula Round (Range *N/elements+0.5);
- wherein Range=2bitin—−bitout—1 where bitin represents the number of input bits for each input pixel in the image data and bitout represents the number of output bits for each pixel in an output image generated by application of the dither matrix data structure to the input pixels in the image data;
- wherein elements=dim_Mtx2 where dim_Mtx represents the dimension of the dither matrix);
- wherein Round represents an operator who rounds off the expression in parentheses to the nearest whole number;
- and
- wherein the parameter N is one of the whole numbers between zero and the dimension of the dither matrix dim13 Mtx, with the values for N associated with each set of X and Y values being a function of the dimension of the dither matrix dim_Mtx.
A method for processing a starting image having a first chromatic resolution and formed by N×M pixels to generate an output image having a second chromatic resolution, the second chromatic resolution being lower than said first chromatic resolution and the starting image including red, green, blue, and luminance groups of pixels, the method comprising:
- generating a first dither matrix;
- including a plurality of first threshold values;
- generating a second dither matrix including a plurality of second threshold values arranged differently than the first threshold values in the first dithering matrix;
- repeatedly applying the first dither matrix to the red, blue, and luminance groups of pixels in the starting image;
- and
- repeatedly applying the second dither matrix to the green group of pixels in the starting image.
Dependencies are inferred from the claim text.