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Efficient Compression of Image/ Graphic All Points A Dressable Files

IP.com Disclosure Number: IPCOM000110604D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Gerlach, RJ: AUTHOR

Abstract

Future applications for personal computers, (electronic encyclopedias, electronic textbooks, and other applications), will require many more images and graphics. The new family of personal computers provides new video modes to accommodate these needs. However, the Direct Access Storage Devices (DASDs) for these computers cannot store a significant number of image/graphic files. IMAGE/GRAPHIC FILES PER DISKETTE PIXELS LINES COLORS BYTES 360k 720k 1.4M 320 200 256 64K + Header 5 11 22 640 350 16 112K + Header 3 6 12 640 480 16 153K + Header 2 4 8 640 480 256 307K + Header 1 2 4

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Efficient Compression of Image/ Graphic All Points A Dressable Files

       Future applications for personal computers, (electronic
encyclopedias, electronic textbooks, and other applications), will
require many more images and graphics.  The new family of personal
computers provides new video modes to accommodate these needs.
However, the Direct Access Storage Devices (DASDs) for these
computers cannot store a significant number of image/graphic files.
                                           IMAGE/GRAPHIC
                                        FILES PER DISKETTE
PIXELS  LINES   COLORS     BYTES        360k     720k    1.4M
 320     200     256     64K + Header     5       11      22
 640     350      16    112K + Header     3        6      12
 640     480      16    153K + Header     2        4       8
 640     480     256    307K + Header     1        2       4

      This article describes a compression algorithm that
significantly compresses the image/graphic files.  The algorithm
capitalizes on these unique properties of image/graphic files.
  1.  All lines are the same length, i.e., 320 pixels.
  2.  Contiguous lines have much data in common.
  3.  A small number of palettes represent a very high percentage of
the colors used.
  4.  Once a palette color is selected it is used for several pixels.
  5.  Chained image/graphic files (i.e., animation) have significant
data in common from one frame to the next.

      The algorithm supplements the palette registers built into the
display adapter electronics which are also a method of compression.
The algorithm is optimized for unpacking speed at the expense of the
time needed to pack the file.  The use of 4-bit tokens to encode the
image data provide easy implementation of the unpack function in
hardware as well as software.

      The packing process starts by scanning the image/graphic file
and building a histogram to indicate the frequency of usage for each
palette color.  Palette colors...