ordered-dithering problem (images included) updated!

[denizen]

why you can not use windows?

[anthony]

I am a linux expert. I avoid windows like the plague! I just hate it!

[denizen]

maybe you can try VMware to emulate windows? it is not so expansive.

[jdnasc]

Hi all,
I've been experiencing this same problem with ordered dithering so I thought I would add some more information in the hope that this will help with debugging and finding a solution.

Several months ago I had been using convert (6.4.3) under OpenSUSE 10.3 to create large GIF animations using ordered-dither (which optimized nicely with -layer optimize). After updating my system to OpenSUSE11.1 the same version of convert (6.4.3) began producing output with the white-space artifacts noted earlier in this thread. Same version, same command. Here is the line from my convert script which performs the ordered-dither:

convert $fnout.miff -ordered-dither o8x8,$clev +map $fnout.gif

where $clev set to produce acceptable looking dithering with a minimum of color levels. Usually somewhere in the range 8-20.

I have tried the suggestions earlier in this thread -- forcing white space to (255,255,255), using a newer version (tried 6.5.8-4 last night), but the same artifacts appear. Using ordered-dither without specifying color levels (o8x8) DOES NOT produce the white space artifacts ! It also produces unacceptably coarse dithering.

I am now using FloydSteinberg dithering, which does not produce the artifacts, but also does not optimize the file size as well. For example a 21Mb GIF animation will optimize (using -layer optimize) to about 3Mb using ordered-dithering, but only to about 18-19Mb using FloydSteinberg. This is a BIG difference (and a big problem if I want to put animations on a website)!

I hope this information is somehow helpful in finding the root of the problem. Again, it only started occuring after updating my system from 10.3 to 11.1, which makes me think it is related to some change in some library (?), but if other users on different systems (Windoze, etc.) are having the same problem I don't know what to think. Any help or suggestions are greatly appreciated. I can provide sample images if necessary, but they basically look like those already posted.

[francois.muller]

Hello, I had some more information about this bug:

- Tested on Ubuntu 9.04 64 Bits ( v6.4.5 ) : bug reproduced
- Tested on Ubuntu 9.04 32Bits ( v6.4.5 ): bug not reproduced
- Tested on Ubuntu 10.04 32 Bits ( v6.5.7-8 ) : bug not reproduced
- Tested on Ubuntu 10.10 64 Bits (v?) : bug reproduced

So it seems that it's a code error on 64 bit machine

command line : convert -ordered-dither o8x8,8 white.png result.png

Regards