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Video Data Path in Color Raster Displays With Variable Pixel Data Structure

IP.com Disclosure Number: IPCOM000060484D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 73K

Publishing Venue

IBM

Related People

Lumelsky, L: AUTHOR

Abstract

Pixel (picture element) data structure heavily depends on the application. The "true color" raster graphics systems are using a direct color definition approach, because it allows the simultaneous use of a virtually unlimited number of colors [1]. In such systems the pixel value in the frame buffer corresponds directly to the value that is sent to the digital-to-analog converters (DACs). The pixel structure is simple and usually includes three equal fields. Conventionally, 8-bit red, green and blue fields are used. For the system with 1K by 1K resolution it requires 24 Mbits of memory. Three-dimensional screen transformations frequently require an additional field, representing depth as a Z-value [2]. Other fields can be included, such as transparency control, screen area identifier, etc.

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Video Data Path in Color Raster Displays With Variable Pixel Data Structure

Pixel (picture element) data structure heavily depends on the application. The "true color" raster graphics systems are using a direct color definition approach, because it allows the simultaneous use of a virtually unlimited number of colors
[1]. In such systems the pixel value in the frame buffer corresponds directly to the value that is sent to the digital-to-analog converters (DACs). The pixel structure is simple and usually includes three equal fields. Conventionally, 8-bit red, green and blue fields are used. For the system with 1K by 1K resolution it requires 24 Mbits of memory. Three-dimensional screen transformations frequently require an additional field, representing depth as a Z-value [2]. Other fields can be included, such as transparency control, screen area identifier, etc. A system with direct color representation and additional attributes may require an impractically large memory. In order to save image memory costs, a color attribute may have less bits. The image quality may be substantially improved by using just one color attribute and adding a fast memory as a video look-up table (VLT), transforming color field data to the longer color output. Some attributes, e.g., transparency field can also be used as input data to the VLT [3], and some, as Z-value, should be removed from the video data path. The built-in hardware- selecting devices can be used for a restricted number of applications, but a set of applications may not even be known completely in advance, especially under research or development circumstances. The video look-up table with address length equal to pixel data length can be used to provide any transformation of necessary fields to the DACs' input data. But VLT memory becomes expensive and hardly achievable with more than 12 bits per pixel. For example, if the 24- bits-per-pixel system were used as a direct definition color system for some applications and as a system with 12-bit color field, 10-bit Z- value and 2-bit transparency field, it would require 48 Mbytes of fast memory for the VLT implementation, i.e., twice more than the frame buffer itself. As a result, there are two major groups of raster displays: systems with direct color definition, and systems using the video look-up table approach. The system described below comprises a video data path which provides an inexpensive way to define the pixel data structure with any layout and number of attribute fields. High flexibility and universalism of a system with such data path allow it to be used for the variety of applications, usually suitable only for one of two major groups of raster displays, or requiring a specially built display. The basic idea of this system is to provide: a combination of several short video look-up tables, each of them; with full length color output, and selection of color fields by means of additional multiplexers; with inputs connected t...