I have a PNG-8 image with transparency, which, due to this problem, I cannot edit in Photoshop (CS5).
Is there a tool that would convert PNG-8 back to PNG-24, preserving transparency layer, so that the file will open correctly in Photoshop?
(The other way to deal with that problem would be to capture a screenshot of any browser displaying that PNG-8 file correctly - but then it would be necessary to induce the transparency layer back, which I'm not sure how is done.)
I don't know of any specific tool for that purpose, but I do know that with GIMP you can open the PNG8 and change the colorspace using the menu path Image->Mode->RGB. Unfortunately I do not have Photoshop to test if the new file is openable myself, however I've provided a version of the sample you provided where the colorspace has been changed so you can give it a try.
https://docs.google.com/open?id=0B6Ad3OCQFyOINmMyOGE0ZmEtMDhjOC00OTZmLWE4M2EtYTYzZmJlZjMyNTA0
Photoshop displays transparency wrong: You've got PNG8 with alpha not supported by Photoshop. For editing, keep PNG in 24-bit, and convert to PNG8+alpha only when done. You can convert PNG8 to 24-bit by resaving it in Preview.app, Fireworks or with: pngout -s1 -c6 -force file.png
The answer comes from http://calendar.perfplanet.com/2010/png-that-works/ under the troubleshooting heading.
I also created a YouTube video to show the process at http://www.youtube.com/watch?v=aCO37zYhEp0.
For a scriptable/command line solution:
After installing GDAL Python Tools (on Linux apt-get install python-gdal)
pct2rgb.py -of PNG -rgba PNG8.png PNG24.png
