Hi - I've just uploaded a vastly improved DCT txcoder: V1.2.  Major points:
 
 *  Encoder now takes .GIF file as input by default
 *  Grey-scale only still; converts colour automatically
 *  Includes own very efficient coding algorithms - very small DCT file size
 *  Still has block discontiguities - no filtering yet
 *  Running about half final decode speed
 
EDCT.EXE encodes a .GIF image into DCT format - type EDCT on its own for
details of switches, etc.  DDCT decodes and displays a .DCT image on a VGA.
Latest compression info:
 
        file   GIF   DCT   ratio    comp bt/px type
 
 alex-10.gif  180K   23K   8.3:1   12.7%  0.77  g/s
tracylrd.gif   93K   12K   7.8:1   12.8%  0.50  g/s
aq-f-022.gif  307K   69K   4.4:1   22.5%  1.80  col
sheshe3a.gif  157K   27K   5.8:1   17.0%  0.70  g/s
  aussie.gif   42K   10K   4.2:1   23.6%  1.25  col
  rimmer.gif  137K   19K   7.1:1   14.0%  0.50  col
  muff03.gif   41K   12K   3.5:1   28.3%  1.48  g/s
ht-s0005.gif  272K   20K  13.7:1    7.3%  0.50  col
 
I expect colour support to approximately double the DCT file size; so it's
true that DCT gives a better deal for mono images.  However, colour DCTs
should still be at least half the size of the GIF.  DCT really wins when
there are large areas of continuous-tone, like a big bum (!).