Browse Prior Art Database

Default RGB Color Palette With Simple Conversion From YUV

IP.com Disclosure Number: IPCOM000102054D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 6 page(s) / 226K

Publishing Venue

IBM

Related People

McFall, JD: AUTHOR [+3]

Abstract

A typical CRT color display can display only a limited number of colors simultaneously, but is capable of selecting the colors from a much larger palette of colors. In a system which requires simultaneous display of different images, the system must use a single set of colors for each image. The present invention provides a technique for selecting a single display palette of a limited number of colors for displaying all images and means for rapidly converting each image from its actual color representation to an image in the preselected limited palette with minimal loss of color distinctiveness.

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Default RGB Color Palette With Simple Conversion From YUV

       A typical CRT color display can display only a limited
number of colors simultaneously, but is capable of selecting the
colors from a much larger palette of colors.  In a system which
requires simultaneous display of different images, the system must
use a single set of colors for each image.  The present invention
provides a technique for selecting a single display palette of a
limited number of colors for displaying all images and means for
rapidly converting each image from its actual color representation to
an image in the preselected limited palette with minimal loss of
color distinctiveness.

      In a typical example, a CRT display may display up to 256
colors simultaneously.  These colors may be selected from an
available palette of up to 256K colors.  In this situation, if each
image was permitted to select its own set of up to 256 colors, it
would clearly be impossible to display two images or portions thereof
on the display simultaneously in any rapidly controlled manner.  By
converting each image to a common single palette of 256 colors,
displaying such images simultaneously is easily managed.

      It has been found that while all color CRT displays have been
standardized to accept tristimulus red, green and blue (RGB) values,
image information can be better compressed and stored in a luminance-
chrominance format in accordance with the International Standards
Organization format using luminance (Y) value and chrominance values
V and U where U=B-Y and V=R-Y.  The preferred relationship between
the tristimulus and luminance-chrominance values is as follows:
                Y = 0.299R + 0.587G + 0.114B
                U = -Cb = B - Y
                V = -Cr = R - Y
 The values are normalized to come within the following
 bounds:
                0 < or = R, G, B < or = 1
                0 < or = Y < or = 1
                -1 < or = U, V < or = 1

      The process of displaying multiple images simultaneously
consists of two basic parts.  In the first part, the tables necessary
for converting the source image from its own selected palette of
colors to the default palette set of colors are built.  In the second
part, images are received and then displayed using the default
palette.

      In the first part, quantizing tables for all the Y, U and V
values are built, and the Y, U and V values that correspond to R, G
and B values that come within the permitted bounds are determined.
Those Y, U and V values that correspond to R, G and B values outside
the permitted bounds are mapped to the closest acceptable R, G and B
values.  After the relationship between Y, U and V values and R, G
and B values have been determined, any duplications are resolved.
Finally, a default palette for the display of all the images is
created.

      In the second part,...