Method and apparatus for correcting unadjusted threshold arrays for halftoning by use of transfer function tables

The present invention relates generally to image forming equipment and is particularly directed to printers of the type which halftone color or monochrome images. The invention is specifically disclosed as a printer that provides a 10-bit unadjusted stochastic threshold array, and applies a Transfer...

Ausführliche Beschreibung

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Bibliographische Detailangaben
Hauptverfasser: Cooper, Brian Edward, Damon, Brian Wesley, Love, Shaun Timothy
Format: Patent
Sprache:eng
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Beschreibung
Zusammenfassung:The present invention relates generally to image forming equipment and is particularly directed to printers of the type which halftone color or monochrome images. The invention is specifically disclosed as a printer that provides a 10-bit unadjusted stochastic threshold array, and applies a Transfer Function Table at run time to the unadjusted array to derive an 8-bit adjusted threshold array, thereby improving perceptual printer response while saving memory space. A printer that stores a minimal number of unadjusted stochastic threshold arrays in non-volatile memory, in which the unadjusted threshold arrays are used to generate adjusted threshold arrays at run time by use of Transfer Function Tables (TFT's). The unadjusted array for a particular color is stored in the printer's ROM and preferably is stored in a packed configuration to save memory space. The TFT's are used to convert the unadjusted threshold data into adjusted threshold data for each color and type of print media. In a preferred embodiment, the unadjusted threshold array comprises a 128 row by 128 column sized array, and each element of this array comprises a 10-bit number. When the TFT is applied to this unadjusted array, the resulting numeric values for the adjusted array elements are produced as 8-bit numeric values. The greater precision in the originating unadjusted array provides more perceptual levels of intensity (i.e., color brightness), which is particularly important at the lighter shades of each color. The adjusted threshold arrays add only the number of dots per gray level (i.e., per differential threshold array level) that are required to provide a printer response that very nearly approximates the human eye perceptual differential response of intensity.