Methods of controlling dot size in digital halftoning with multi-cell threshold arrays
First Claim
1. A method of displaying a high quality image on a raster display device having predetermined gray levels made up of halftone dots of substantially equal shape and size in a supertile that includes K digital cells, each supertile having a geometric center of gravity, K corresponding ideal cells each having geometric centers and a plurality of pixels having coordinates to reproduce the image by applying a spot function selected from a wide range of spot functions to the coordinates of a selected list of pixels, comprising the steps of:
- a) creating a list of pixels in a digital cell;
b) determining the x and y coordinates in cell space of the pixels in the said digital cell;
c) determining an offset vector having x and y coordinates to be applied to said pixel coordinates in cell space of that digital cell;
d) adding said offset vector to the coordinates of said pixels in said list;
e) selecting a spot function from a wide variety of spot functions;
f) ranking said pixels in said list according to the value resulting from applying said selected spot function to their coordinates;
g) selecting pixels for display according to the results of said ranking in order to properly reproduce said predetermined gray levels of the image being reproduced; and
h) displaying a high quality image including the pixels that have been selected for display using a ranking resulting from applying a spot function selected from a wide range of spot functions.
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Abstract
A method of equalizing the shape and size of halftone dots in a supertile having digital cells, corresponding ideal cells and pixels to faithfully reproduce an image having predetermined gray levels. Various techniques include: (1) adding offset vectors to the coordinates of pixels in digital cells; (2) determining twice as many smaller digital cells as original digital cells; and (3) determining a model digital cell and ranking pixels in remaining digital cells to mimic the ranking of pixels in the model cell.
35 Citations
19 Claims
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1. A method of displaying a high quality image on a raster display device having predetermined gray levels made up of halftone dots of substantially equal shape and size in a supertile that includes K digital cells, each supertile having a geometric center of gravity, K corresponding ideal cells each having geometric centers and a plurality of pixels having coordinates to reproduce the image by applying a spot function selected from a wide range of spot functions to the coordinates of a selected list of pixels, comprising the steps of:
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a) creating a list of pixels in a digital cell; b) determining the x and y coordinates in cell space of the pixels in the said digital cell; c) determining an offset vector having x and y coordinates to be applied to said pixel coordinates in cell space of that digital cell; d) adding said offset vector to the coordinates of said pixels in said list; e) selecting a spot function from a wide variety of spot functions; f) ranking said pixels in said list according to the value resulting from applying said selected spot function to their coordinates; g) selecting pixels for display according to the results of said ranking in order to properly reproduce said predetermined gray levels of the image being reproduced; and h) displaying a high quality image including the pixels that have been selected for display using a ranking resulting from applying a spot function selected from a wide range of spot functions. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of displaying an image on a raster display device having predetermined gray levels made up of halftone dots of substantially equal shape and size in a supertile which represent predetermined gray levels of the image being displayed, said supertile including a predetermined number of digital cells of a first type in a first digital halftone grid and twice said predetermined number of digital cells of a second type in a second digital halftone grid, each of said digital cells having a plurality of pixels, comprising the steps of:
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a) assigning an equal number of pixels to each of said second type of digital cells; b) computing a threshold value for each pixel in each of said digital cells of said second type; and c) comparing said threshold values to said gray levels and on the basis of the results of that comparison, selecting the pixels for display in order to properly reproduce said predetermined gray levels of the image; and d) displaying the image including the pixels selected for display. - View Dependent Claims (11, 12, 13, 14)
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15. A method of displaying an image on a raster display device having predetermined gray levels made up of halftone dots of substantially equal shape and size in a supertile that includes a predetermined number of digital cells, each digital cell having a plurality of pixels, a first of said digital cells and each remaining digital cell having a cell data structure representing pixels which allows the operations of sorting, ranking and selecting pixels of predetermined rank, comprising the steps of:
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a) selecting a spot function from a wide variety of spot functions; b) ranking the plurality of pixels in said first digital cell according to the value resulting from applying said selected spot function to their cell space coordinates to establish for the plurality of pixels for such cell a first rank order; c) ranking the plurality of pixels in the remaining digital cells in the same manner as for said first digital cell to provide a first ranking for the plurality of pixels of each said remaining digital cells; d) for each of said remaining digital cells, selecting one pixel from the plurality of pixels in each such cell which was assigned the lowest rank in step c), above, and assigning said one pixel, a second rank which is as low as possible; e) iteratively ranking the remaining pixels in each of said remaining digital cells so that a given pixel of each such remaining cell is assigned a given second rank, where the number of previously second-ranked pixels contiguous to said given pixel is approximately equal to a number of pixels in said first digital cell which are;
(1) contiguous to a pixel whose first rank in said first rank order is equal to said given second rank of said given pixel; and
(2) which itself has a rank less than or equal to said given second rank, thereby establishing a second ranking of pixels;f) selecting pixels for display according to the results of said given second ranking for the purpose of properly reproducing said predetermined gray levels of the image; and g) displaying the image including the pixels that have been selected for display using a ranking resulting from applying a spot function selected from a wide range of spot functions. - View Dependent Claims (16, 17, 18, 19)
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Specification