2002.03.05 14:53 "Photoshop Alpha Channel", by Phil Hulme

2002.03.06 01:36 "Re: Photoshop Alpha Channel", by Chris Cox

I'm not sure if this is what Phil was referring to, but PhotoShop has the most pathetic handling of alpha I can imagine. Here's a simple one:

First, alpha is not the same as transparency. Transparency is a subset of possible alpha channels.

  1. Open a blank image
  2. Draw anything on it. Make it small enough that you can see the background checker pattern.
  3. Save it as a PSD.
  4. Save it as a TIFF.
  5. Open both the PSD and TIFF and compare them. The PSD will maintain the alpha channel while the TIFF file will have been merged over white with no sign of transparency.

Second, you didn't save the TIFF with transparency. If you save the TIFF with transparency, it won't be flattened.

This is inexcusable.

This is user error.

I should be able to save a TIFF, PNG, or TGA and still have my alpha channel.

No, you should still have transparency.

PNG and TGA support transparency, not arbitrary alpha channels. TIFF supports transparency AND arbitrary alpha channels.

Of course, if you open a TIFF file that has a proper associated alpha channel, PhotoShop will properly display the image. Too bad you then have to save it as a PSD in order to maintain the alpha.

You don't have to do that - as explained in your manual. In Photoshop 6, TIFF and PNG handle transparency just fine. TGA did not, that was a bug (it wrote the first alpha channel into the transparency slot and read it back as an alpha channel instead of transparency). That is fixed in PS 7.