Am Wed, 19 Nov 2014 00:35:09 +0100
schrieb Marco Leise <marco.le...@gmx.de>:

> > I have working PNG export in my image processing package, part of dlib: 
> > https://github.com/gecko0307/dlib
> > There're also importers for BMP and TGA.
> 
> I also just wrote a TGA importer and found RLE and 16-bit in
> particular badly supported on Linux. E.g. eye-of-gnome
> (Gnome's picture viewer) doesn't correctly restore the last
> pixel's color in an RLE image and most software doesn't handle
> 16-bit at all. Add to that, that the specs are not very
> specific as to what allowed values are and you get all
> sorts of funny implementations quirks.
 
For example:
- the original Targa paint software TIPS used to store a
  palette even for TrueColor images, meaning you should
  actually calculate the data offset as header + id + palette
  even for 24- and 32-bit images.
- the number of channels for a TrueColor TGA is always 3, plus
  as many attribute bits as given in the descriptor.

If you only support 8-bits per color channel, you should check
if bitsPerPixel is >= 24. Otherwise, bitsPerPixel == 16 would
be interpreted as a two color channel image instead of three
channels à 5-bits. And bitsPerPixel == 15 would become a one
channel image. :p
The 15-/16-bit variants were used quite a bit in the early
days of 3D games, like in the menu graphics for "Trespasser".
They are the same except that 16-bit allows for an additional
attribute bit that could be used for a transparency mask.

-- 
Marco

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