Dither method and apparatus
First Claim
1. A method of creating a three dimensional halftone dither matrix, said matrix being divided into a predetermined number of levels with each level comprising a two dimensional matrix of activation indicators having positional values including x and y positional components, said method being performed using a computer and comprising the steps of:
- (a) creating a series of three dimensional curves, from a two dimensional array of dither values, said two dimensional array being of the same dimensions as said two dimensional matrix and comprising level value entries, each of said level value entries having a corresponding three dimensional curve, said three dimensional curve starting at a starting level corresponding to said dither matrix value and at a position corresponding to the x and y positional components of said level value entry, said three dimensional curve terminating on the highest level of said three dimensional halftone dither matrix and taking one x and y positional value on each level between said starting level and said highest level,(b) forming an objective function having at least two components, a first component being a measure of the evenness of the distribution of the positional values of said curves for a particular level, and the second component being a measure of the deviation of said curve from a straight vertical line,(c) optimising said objective function so that the positional values at any of said levels of said series of curves have a high degree of evenness of distribution and said curves have a low degree of deviation from a straight vertical line, and(d) forming said three dimensional halftone dither matrix wherein said activation indicators are active in positions corresponding to the paths of each of said curves.
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Abstract
A method of creating a three dimensional halftone dither matrix, in which the matrix is divided into a predetermined number of levels with each level comprising a two dimensional matrix of activation indicators having positional values including x and y positional components. The method includes the steps of firstly creating a series of three dimensional curves, from a two dimensional array of dither values, the two dimensional array being of the same dimensions as the two dimensional matrix and including level value entries, each of the level value entries having a corresponding three dimensional curve, the three dimensional curve starting at a starting level corresponding to the dither matrix value and at a position corresponding to the x and y positional components of the level value entry, the three dimensional curve terminating at the highest level of the three dimensional halftone dither matrix and taking one x and y positional value on each level between the starting level and the highest level. Secondly, the method forms an objective function having at least two components, a first component being a measure of the evenness of the distribution of the positional values of the curves for a particular level, and the second component being a measure of the deviation of the curve from a straight vertical line. Thirdly, the method optimizes the objective function so that the positional values at any of the levels of the series of curves have a high degree of evenness of distribution and the curves have a low degree of deviation from a straight vertical line. Lastly, the method forms the three dimensional halftone dither matrix wherein the activation indicators are active in positions corresponding to the paths of each of the curves.
19 Citations
11 Claims
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1. A method of creating a three dimensional halftone dither matrix, said matrix being divided into a predetermined number of levels with each level comprising a two dimensional matrix of activation indicators having positional values including x and y positional components, said method being performed using a computer and comprising the steps of:
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(a) creating a series of three dimensional curves, from a two dimensional array of dither values, said two dimensional array being of the same dimensions as said two dimensional matrix and comprising level value entries, each of said level value entries having a corresponding three dimensional curve, said three dimensional curve starting at a starting level corresponding to said dither matrix value and at a position corresponding to the x and y positional components of said level value entry, said three dimensional curve terminating on the highest level of said three dimensional halftone dither matrix and taking one x and y positional value on each level between said starting level and said highest level, (b) forming an objective function having at least two components, a first component being a measure of the evenness of the distribution of the positional values of said curves for a particular level, and the second component being a measure of the deviation of said curve from a straight vertical line, (c) optimising said objective function so that the positional values at any of said levels of said series of curves have a high degree of evenness of distribution and said curves have a low degree of deviation from a straight vertical line, and (d) forming said three dimensional halftone dither matrix wherein said activation indicators are active in positions corresponding to the paths of each of said curves. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for halftoning an input image comprising:
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an inputting device for inputting pixel data values including intensity level and address data, a table look up device, connected to said inputting device, and containing a series of two-dimensional arrays of dither values comprising level value entries, each of said level value entries having a corresponding three-dimensional curve starting at a starting level corresponding to a three-dimensional halftone dither matrix value and at a position corresponding to x and y positional components of said level value entry, said three-dimensional curve terminating on a highest level of said three-dimensional halftone dither matrix and taking one x and y positional value on each level between said starting level and said highest level wherein said level value entries have been optimised so that said level value entries of said curves have a high degree of evenness of distribution and said curves have a low degree of deviation from a straight vertical line, said intensity level data being used to select one of said series of two-dimensional arrays and address data being used to address a data value within said selected two-dimensional array, and a marking device, connected to said look-up device, for making an output image when said data value exceeds a predetermined threshold.
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Specification