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FAST CHANGES IN A DISPLAYED FLOYD-HALFTONE

IP.com Disclosure Number: IPCOM000025291D
Original Publication Date: 1984-Jun-30
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 116K

Publishing Venue

Xerox Disclosure Journal

Abstract

A preferred method to display a grey scale image on a one bit/pixel screen is to use a Floyd type two dimensional halftone. However, because the halftone is created by an error diffusion process, it is difficult to introduce in real time local changes in the display, as needed by airbrushing methods, without affecting the quality of the display. A method is described which minimizes the visible artifacts in the display when local changes are made.

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KEROX DISCLOSURE JOURNAL

FAST CHANGES IN A DISPLAYED

358/260 CI. US. Proposed FLOYD-HALFTONE Dorian Kermisch Classification

Int. C1. H04n 1/00

A preferred method to display a grey scale image on a one bit/pixel screen is to use a Floyd type two dimensional halftone. However, because the halftone is created by an error diffusion process, it is difficult to introduce in real time local changes in the display, as needed by airbrushing methods, without affecting the quality of the display. A method is described which minimizes the visible artifacts in the display when local changes are made.

As needed with airbrushing techniques, the image or part of it, is stored in a computer buffer. To display the image, a Floyd halftoning procedure is run. This procedure, usually in microcode, halftones one line at a time. As each line is halftoned, the procedure stores into an error buffer the errors to be used when halftoning the next line. Sometimes it is desired to refresh, with changed pixel values, only part of the display. However, unless the errors diffused to the starting line of the refresh are known, certain artifacts appear in the display. The artifacts are caused by the discontinuity in the error diffusion.

To store all the errors in a buffer is impractical. The errors are represented by integers, and the required buffer has to be 16 times larger than the display buffer. A compromise between refresh speed and the size of the available buffer can be achieved if only every nth line of errors is stored. For n=16, for example, the size of the error storage buffer is equal to that of the display buffer. If it is desired to start a refresh of display from an image line which is a multiple of n, the stored error line can be used, transferred into the error buffer, and the haltoning process from that line down can be started. Because the correct line of errors is used, the display will not have any artifacts.

When airbrushing is performed, the pixels within a given local area, indicated by the cursor, are changed whenever a given mouse key is pressed or when the key stays pressed and the cursor position changes. To speed up the displayed changes, as long as that key is pressed, a different procedure Floyd-halftones only the area under the cursor, using as initial...