Legacy ImageMagick Discussions Archive

IM 6.5.3-2 Q16 Mac OSX Tiger.

(Two possible bugs)

First potential bug. I am not getting what I believe should be the correct behavior when convert a Class: DirectClass and Type: GrayscaleMatte PNG (with alpha channel) to PNG8 (expecting Class Pseudoclass and Type: GrayscaleMatte) so as to get a smaller filesize.

Here is the image I got from http://studio.imagemagick.org/pipermail ... 22567.html

Original


I removed the alpha channel to see what was there and also extracted the alpha channel:

Image without alpha:
convert jobs_original.png -alpha off jobs_original_aoff.png


Image alpha channel:
convert jobs_original.png -alpha extract jobs_original_alpha.png


So looks fine to me.

Now when I do:
convert jobs_original.png PNG8:jobs_original_png8.png


It is not what I expected

But when I make it gif, it looks like what I expected:
convert jobs_original.png jobs_original.gif


And if I do:
convert jobs_original.png GIF:- | convert - jobs_original_gif_png.png


The above also looks right and is of Class Pseudoclass and Type: GrayscaleMatte (so smaller filesize)




Second potential bug. When I do

convert jobs_original.png GIF:- | convert - PNG8:jobs_original_gif_png8.png

I now get an error message:
coders/png.c:6990: failed assertion `(unsigned long) packet_index < number_colors'
Abort trap

Is there any further information about these two bug reports? Have they been validated? Are they bugs or am I misunderstanding something?

Thanks.

Fred

We forwarded this bug to glennrp. He is the current maintainer of the PNG module. Feel free to ping him about the problem. If you need an address, send a PM.