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Exception
03-23-2005, 02:34 PM
Hi guys,

Has anyone the same problem like me, when over the last 3 versions of Lightwave (6, 7 and 8), when a 32 bits tiff is saved and opened up in PS, the alpha channel is applied to the image as a transparency channel and then subsequently lost. So, the alpha info is there, yes, but not as an alpha channel but as transparent pixels.

I find this quite irritating to say the least. Apparently it is a property of the LW tiff saver and not of the PS tiff loader. All other tiffs with alpha channel saved by other programs load fine.

Snosrap
03-23-2005, 04:02 PM
I thought this was essentially how alpha channels worked. For the last 3 years or so I've been rendering in PNG32 and prior to that TGA's. I never render in Tiff so I can't speak for how the alpha channel works. However I have found that various software venders handle alpha channel differently. I've included a 3 samples of the same rendered PNG 32 frame for comparison. Notice that Photoshop ignores the rendered Bloom effect completely, while Photopaint recognizes it but cuts it out when creating an object from the mask. (Photopaint refers to it's layers as objects). And then notice Mirages interpretation of the alpha. In my opinion this is what is desirable. Again I'm no expert on alpha channels I just use what seems to work and for me and Mirage seems to work.

Snos

Exception
03-24-2005, 03:52 AM
Well, the thing is, the alpha-ed out parts of an image contain information too. when a LW saved tiff is opened in PS, that information is lost. Photoshop has an official alpha channel layer in which the alpha channel should appear. No transprarency should be applied at all.

maxxwv
03-24-2005, 08:09 AM
Well, the thing is, the alpha-ed out parts of an image contain information too. when a LW saved tiff is opened in PS, that information is lost. Photoshop has an official alpha channel layer in which the alpha channel should appear. No transprarency should be applied at all.

I agree entirely. Up until last week, I was still on PS 5.0, which handled the alpha info the correct way - it came in as an alpha channel, not just knocked out image space. Imagine my chagrin at the way CS does it now. :mad:

Basically just agreeing and subscribing to this thread so that if someone has an answer on how to fix it, I can reap the benefits as well!

nemac4
03-25-2005, 10:32 PM
In photoshop, all you have to do is control click the layer icon to select the image in the layer,.. then under the channel tab, click the Make Alpha from Selection button at the bottom of the pallet. If you get any fringing on the edges of your alpha, just create a black filled background layer behind the image layer.,. but generally it is fine.

Gimp will import/export the alpha in the normal way.

Also,.. I believe if you save out to the tiff format from photshop it will still contain the "hidden" alpha. I'd have to test it to be sure.

edt: OK,.. I tested it and PS does still save the Tiff alpha. Which means ,.. if you stay in the tiff format you'll be fine,.. but if you need to modify the alpha you'll have to rebuild it from the selection or save it as a PSD ( or use another app ). The tiff alpha is just based on tranparency as far as photoshop is concerned. But it is still embedded,.. so if you erase some of the image it will not be added to the alpha.