GNOME Bugzilla – Bug 152456
Better support for partial transparency in indexed images
Last modified: 2004-09-13 17:22:17 UTC
For example, try opening this image in the GIMP: http://www.masmodels.com/images/port-frame-norm-fs8.png Although it is indexed, given the current limitation of indexed images only containing 1 bit alpha, it would seem to make sense to give the option to open it as a 32-bit rgba image. For example, a dialog with text such as this could be presented when the user tried to open such an image: Image foo.png is indexed, with alpha transparency. Unfortunately this version of the GIMP cannot edit indexed images with alpha channels. Do you wish to: * Open as an indexed image and loose some transpaency information * Open as an rgb image, which can express the image exactly but increases the filesize
There's a bit of confusion here. It actually is not really true that indexed images can only contain 1 bit alpha. What *is* true is that GIMP *displays* indexed images as though they contained 1 bit alpha. It does this because of a bug in Internet Explorer: GIMP shows you the image the way it would look if you viewed it in IE. GIMP does this in order to protect you from creating images that look wrong in the most widely used browser. Pretty much the only reason people create indexed images is for browsers, so this is important. What is also true is that if you convert an image from Indexed to RGB mode in GIMP, your options are either no transparency or 1 bit transparency. GIMP enforces this restriction for the same reason as above: to keep you from creating things that IE doesn't support properly. Actually, your image is being loaded in a completely correct way, and if you convert it to RGB mode after loading, you will see that all the information is there. You just don't see it as long as you are in indexed mode. I know it's strange and confusing. Blame Microsoft.
This seems absolutely bizare to me - for image editing software to assume it knows beter than the user what the images are for. At the very least this behaviour should be an option. For example a combobox labelled "view as would be displayed in..." on the image window. Restricting everyone to the lowest common denominator seems wrong. In my webpages I serve image formats (Gif, PNG32, PNG8) based on content negotiation. I am aware of the limitations of IE (and some other, older browsers), but don't want my image editing software to double guess what I'm trying to do. Is it the case that I simply cannot hand-tune an 8bit, indexed image in the GIMP? I blame MS for IE not showing PNGs properly, and a bunch of other stuff, but not this!
Bill, it is actually not Microsoft who is to blame here. The way that indexed images are handles in GIMP was designed for handling GIF images. At the time when this decision was made and this code was written, the GIF format was the format for indexed images with transparency and it only supports 1bit transparency. Noone really likes how indexed images are handled but so far none of the developers cares enough to change it. I would actually prefer to see support for indexed images removed from the GIMP core and let the file plug-ins handle the conversion.
Okay, I stand corrected. I will reopen this bug, changing the summary and priority according to the real issue.
It basically has become a duplicate of bug #86627 then.
*** This bug has been marked as a duplicate of 86627 ***