Comment 1 Carolyn MacLeod 2005-11-09 11:55:16 EST

Created attachment 29610 [details]
A Depth 1 GIF

Comment 2 Carolyn MacLeod 2005-11-09 11:56:00 EST

Created attachment 29611 [details]
A Depth 1 PNG

Comment 3 Carolyn MacLeod 2005-11-09 11:56:59 EST

Created attachment 29612 [details]
A Yellow/Blue Depth 1 PNG

Comment 4 Carolyn MacLeod 2005-11-09 11:57:58 EST

Created attachment 29614 [details]
Another Depth 1 GIF (Red X)

Comment 5 Carolyn MacLeod 2005-11-09 11:58:55 EST

Created attachment 29616 [details]
Another Depth 1 GIF (Harp)

Comment 6 Valentin Schnitzer 2006-03-31 15:27:11 EST

The first thing which came to my mind was that the code size with which 
the decoding is started is wrong.
 From the GIF87a Specification:

Establish Code Size

The first byte of the GIF Raster Data stream is a value indicating the 
minimum number of bits required to represent the set of actual pixel 
values. Normally this will be the same as the number of color bits. 
Because of some algorithmic constraints however, black & white images 
which have one color bit must be indicated as having a code size of 2. 
This code size value also implies that the compression codes must start 
out one bit longer.

After stepping through the code I found the part which needs to be 
altered:
LZWCodec.java in the function initializeForEncoding.
Line 250: codeSize = bitsPerPixel + 1;
In: if (bitsPerPixel==1) codeSize=3 else codeSize = bitsPerPixel + 1;
Or something similar.

I hope this solves the problem.
Greetings, Valentin

Comment 7 Valentin Schnitzer 2006-03-31 15:29:11 EST

The first thing which came to my mind was that the code size with which 
the decoding is started is wrong.
 From the GIF87a Specification:

Establish Code Size

The first byte of the GIF Raster Data stream is a value indicating the 
minimum number of bits required to represent the set of actual pixel 
values. Normally this will be the same as the number of color bits. 
Because of some algorithmic constraints however, black & white images 
which have one color bit must be indicated as having a code size of 2. 
This code size value also implies that the compression codes must start 
out one bit longer.

After stepping through the code I found the part which needs to be 
altered:
LZWCodec.java in the function initializeForEncoding.
Line 250: codeSize = bitsPerPixel + 1;
In: if (bitsPerPixel==1) codeSize=3 else codeSize = bitsPerPixel + 1;
Or something similar.

I hope this solves the problem.

Comment 8 Conny Kreyssel 2007-01-26 05:07:15 EST

Can anyone tell me if a patch is available? I need urgently to write depth 1 gif's!

Thanx

Comment 9 Conny Kreyssel 2007-03-29 04:09:51 EDT

No comments?

Comment 10 Carolyn MacLeod 2007-04-09 17:04:21 EDT

Unfortunately, the patch doesn't work, and I don't have time at this point to spend more time on it. If someone could submit a working patch, then I do have time to retest and commit.

Comment 11 Eclipse Webmaster 2019-09-06 16:06:11 EDT

This bug hasn't had any activity in quite some time. Maybe the problem got resolved, was a duplicate of something else, or became less pressing for some reason - or maybe it's still relevant but just hasn't been looked at yet.

If you have further information on the current state of the bug, please add it. The information can be, for example, that the problem still occurs, that you still want the feature, that more information is needed, or that the bug is (for whatever reason) no longer relevant.