Browse Prior Art Database

Color Pallette Expansion Technique for a Windowed Environment

IP.com Disclosure Number: IPCOM000122548D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 100K

Publishing Venue

IBM

Related People

Beattie, I: AUTHOR [+3]

Abstract

This article describes a method of effectively expanding the number of 8-bit Red/Green/Blue (R/G/B) color palettes available in a RAMDAC having a basic R/G/B palette of 256 active colors. This configuration must be able to support 8-bit R/G/B, 8-bit Indexed, and 24-bit R/G/B color modes in a windowed environment. The later two (8-bit Indexed and 24-bit R/G/B) consume the total palette (3 x 256). Only in the case of 8-bit R/G/B can the disclosed technique be used. Dynamic switching between the different color modes is required because multiple visible windows may require different color modes.

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This is the abbreviated version, containing approximately 52% of the total text.

Color Pallette Expansion Technique for a Windowed Environment

      This article describes a method of effectively expanding
the number of 8-bit Red/Green/Blue (R/G/B) color palettes available
in a RAMDAC having a basic R/G/B palette of 256 active colors.  This
configuration must be able to support 8-bit R/G/B, 8-bit Indexed, and
24-bit R/G/B color modes in a windowed environment.  The later two
(8-bit Indexed and 24-bit R/G/B) consume the total palette (3 x 256).
Only in the case of 8-bit R/G/B can the disclosed technique be used.
Dynamic switching between the different color modes is required
because multiple visible windows may require different color modes.

      In the figure, two types of frame buffers are implied. The base
frame buffer is always present and is used to store either 8-bit
R/G/B or 8-bit Indexed color data or the red component only for
24-bit mode.  Data lines designated 'Dx' originate from the base
frame buffer.  The 'optional frame buffers' are not always present,
but when they are, then, and only then, can the 24-bit R/G/B mode be
supported.  Data lines designated 'Dx/A' and 'Dx/B' originate from
the optional frame buffer if it is present.  In addition, a control
plane block is also required which contains the window I.D.(WIDx)
bits.  For each pixel location on the screen, a 4-bit WID defines
which of 16 windows is assigned to each pixel.  A RAM driven by the
WID bits is used to specify on a per window basis what resources are
assigned to which window.  As indicated, an output from this RAM is
used to specify if a particular window is running in 8-bit R/G/B mode
vs. one of the other color modes, as well as whether the optional
frame buffer is present.

      As shown in the figure, there are three palette SRAM components
(red, green, and blue).  The inputs to these SRAM are the address
lines, and the output dr...