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COLOR Image Processing for a Printer With a Multi-Line Printhead

IP.com Disclosure Number: IPCOM000060388D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 7 page(s) / 57K

Publishing Venue

IBM

Related People

Daniels, PR: AUTHOR

Abstract

A method is described for processing color image data (pel data) from an input format to a format which is transferred directly to the multi- line printhead for subsequent printing to matrix color printing technologies, such as resistive ribbon thermal transfer, that use a multi- line printhead and a ribbon with multiple color tracks. The specific items disclosed are the data structures and the processes unique for color image data. A typical resistive ribbon thermal transfer printer which makes use of the arrangement described contains a printhead with 120 equally spaced electrodes which span a vertical dimension of one-half inch. Such a printhead is typically used to simultaneously print three text lines at 6 lines/inch, 4 text lines at 8 lines/inch, etc.

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COLOR Image Processing for a Printer With a Multi-Line Printhead

A method is described for processing color image data (pel data) from an input format to a format which is transferred directly to the multi- line printhead for subsequent printing to matrix color printing technologies, such as resistive ribbon thermal transfer, that use a multi- line printhead and a ribbon with multiple color tracks. The specific items disclosed are the data structures and the processes unique for color image data. A typical resistive ribbon thermal transfer printer which makes use of the arrangement described contains a printhead with 120 equally spaced electrodes which span a vertical dimension of one-half inch. Such a printhead is typically used to simultaneously print three text lines at 6 lines/inch, 4 text lines at 8 lines/inch, etc. For monochrome printing, the ribbon used with such a printer is all black with a width which exceeds the half-inch printhead height by an amount sufficient to compensate for manufacturing and positioning tolerances. For color printing, the ribbon contains four color tracks, one for black plus one for each of the primary colors (additive or subtractive). Another typical color ribbon arrangement has only three color tracks and is not able to print black. In either case, the ribbon width exceeds the printhead height by an amount which is the same as the black ribbon. A significant difference in usage between the color ribbon and the black ribbon is the ability to print across the entire width. Because of manufacturing tolerances and color track positioning tolerances with respect to the printhead, a portion of ribbon at the interface between different colors cannot be used. This is due to the uncertainty as to which of the two colors on either side of the interface will be aligned with which electrodes. This area of ribbon is referred to as a guard band. Typical widths of a guard band, relative to the printhead resolution, are 8 to 16 pels high centered on the nominal position of the color band interfaces. A typical printer which makes use of the matrix technology contains a swath buffer as a key component. A swath is defined as the two-dimensional matrix of pel data placed on the paper during each horizontal pass of the printhead across the paper. For a 120- electrode printhead, the swath is 120 pels high by a number of pels wide which equals the product of the maximum printline and the horizontal print resolution in pels per inch. The swath buffer is a unit of storage which contains the pel data for a swath. Data is transferred from this swath buffer to the printhead by columns with each column delivered to the printhead at a rate which corresponds to the print speed and the horizontal resolution. The following assumptions are descriptions to facilitate an understanding of the processes and as bases for illustrative examples. 1. A swath buffer is contained in the basic printer electronics and is not unique for colo...