Browse Prior Art Database

Halftoning Method for Mosaic Color Displays Using Error Diffusion

IP.com Disclosure Number: IPCOM000036519D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 5 page(s) / 48K

Publishing Venue

IBM

Related People

Feigenblatt, RI: AUTHOR

Abstract

The standard method for implementing color on liquid crystal displays, the dominant flat panel technology, is to use a mosaic array of primary color pixels. A careful scheme is required to map the standard image triplet of primary contiguous arrays to the mosaic. This is even more true when basic or practical issues limit the grey level response of the pixels. The following describes such a method based on the mosaic- channeled propagation of round-off errors between pixels.

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Halftoning Method for Mosaic Color Displays Using Error Diffusion

The standard method for implementing color on liquid crystal displays, the dominant flat panel technology, is to use a mosaic array of primary color pixels. A careful scheme is required to map the standard image triplet of primary contiguous arrays to the mosaic. This is even more true when basic or practical issues limit the grey level response of the pixels. The following describes such a method based on the mosaic- channeled propagation of round-off errors between pixels.

In recent years it has become clear that few display applications of interest can forego the advantages made possible by (multi)color. The dominant form of electronic display today, the raster-scanned, continuously-refreshed CRT, realizes color well. However, it is more than possible that by the end of this century, this device will have been replaced in most applications by some sort of liquid-crystal light-modulator addressed by a regular matrix.

Color liquid crystal displays have been built by optically co- projecting the image of several valves at the expense of surrendering the compactness which give LCDs their appeal. Frame-sequential color might yet prove practical with LCDs at the expense of tripled switching speeds. However, to date ALL flat panel LCDs have used a repeating mosaic of color filters to achieve color operation, making examination of this case of primary interest. Study of LCD mosaic color has been reported 1, 2, 3 in the last few years. It is related to the design of single-CRT and single-chip video cameras, which also rely on a color mosaic to encode color information [4].

The problem of color mosaic representation of images has at least two parts: design of a suitable mosaic and choice of a particular mapping scheme between the image and the mosaic.

A method of solving the second problem for a particular solution of the first problem is described. Some examples relate to a repeating color mosaic of three primaries with the following particular nine- pixel repeat pattern: R G B

B R G

G B R

The cited examples assume the pixels are binary, either on or off. Extension of the methods taught herein from this mosaic to others is discussed after the main design examples are explained.

True full-color imaging requires the presence of grey level. Unfortunately, some of the most promising liquid crystal phenomena being explored for liquid crystal display application are rather unamenable to grey level, such as the smectic-C ferroelectric effect of recent great interest. Moreover, even when other methods (such as TFT active matrix) admit grey level in principle, practical considerations of uniformity and yield may greatly limit the number of levels which can be economically achieved.

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The representation of grey-level images via media which are inherently amplitude quantized has long been of interest to the information display community. For centruries bilevelism has bee...