The specifications (plural, since there are versions 87a and 89a) of the GIF graphics format are easy to find in the internet (for those who don't want to google:
As you can see in the specification GIF has support for some features that I have never seen used; I only want to give two examples (for simplicity from GIF 89a): - Plaintext extension: on http://www.vias.org/pngguide/chapter11_15.html there is a little bit more detailed documentation - Pixel Aspect Ratio: see section 18. Logical Screen Descriptor. of GIF 89a specification
On the other hand, for PNG there seem to be lots of test images available: http://www.libpng.org/pub/png/pngmisc.html (scroll down); the most common one is the official PNG test suite http://www.schaik.com/pngsuite/ that is also mirrored at http://www.libpng.org/pub/png/pngsuite.html.
What I am looking for is a test suite of GIF images that also/especially contains images using features that are rarely used or often implemented in a wrong way.
The best results that I could find in the internet are the following:
- Images linked from http://en.wikipedia.org/w/index.php?title=Graphics_Interchange_Format - among them images using some not-so common GIF features
- http://phil.ipal.org/tc217.gif (as an example how to use 24 bit depth in GIF files) - linked from http://phil.ipal.org/tc.html and referenced in http://en.wikipedia.org/w/index.php?title=Graphics_Interchange_Format&oldid=411332804#cite_note-8)
- The file http://www-eng-x.llnl.gov/documents/a_image.gif (referenced in http://www-eng-x.llnl.gov/documents/tests/gif.html) claims this to be a test image; for me it rather looks like it is from a time when GIF support was not common in browsers
- Under http://www.fileformat.info/format/gif/sample/index.htm there are files called "GIF Sample Files"; it doesn't look to me that they use more than the "very common" features of GIF
So I could find nothing fullfilling the above stated criterion of a test suite of GIF images also/especially containing features that are rarely used or often implemented in a wrong way.
So: do you know of such a test suite?
I was searching for the same thing and came across this page:
http://code.google.com/p/imagetestsuite/
It contains test suites for PNG/GIF/JPEG/TIFF created so that they try to achieve maximum amount of code coverage with the least amount of images based on the open source decoder code-bases. The idea seems good, but I have not yet had time to check out the actual images.