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PS and alpha channels

Posted: 15 Nov 2007, 04:21
by rattle
Simple question: why does PS (CS2) have fixed alpha values?

It goes like this: 16, 17, 18, 19, 20 become 16, 18, 21. I can't work with that...

Posted: 15 Nov 2007, 08:03
by KDR_11k
Interesting, I've never seen that happen.

Posted: 15 Nov 2007, 12:43
by Wolf-In-Exile
I'm not quite sure what you mean by fixed alpha values, could you explain your problem further?

Re: PS and alpha channels

Posted: 15 Nov 2007, 15:05
by Pxtl
rattle wrote:Simple question: why does PS (CS2) have fixed alpha values?

It goes like this: 16, 17, 18, 19, 20 become 16, 18, 21. I can't work with that...
I'm going to assume you mean 16,17, etc. as bytes. I think PS stores alpha as a percentage, so it degrades the 0-255 to only 0-100. Really, one feature that has always been a problem in Photoshop is that it treats alpha like a special, magical concept instead of just another channel.

Posted: 15 Nov 2007, 16:42
by rattle
17 becomes 16, 19 becomes 18, 20 becomes 21, ...
Get the pencil tool out, draw or fill an area with color 17, hit ALT and get the color (or use the color picker) and check what it is now. It's 16. And it's not a percentage, goes up to 255.

I tried changing the layer with no success. Copy pasta degrades the color values too.

Kinda out of clues now... changing the alpha channel behavior does not change a thing either. I don't know how it was in previous versions of PS because I never needed explicit alpha values.

Posted: 15 Nov 2007, 21:49
by rattle
This is still present in PS10, not in PS7 though. Great, I need PS8 or PS9 at least for gradient maps, but can't do proper alpha channels in them. :(

Maybe it's time to look at GIMP, if it has gradient maps that is. Cba to color in my textures manually.

Posted: 15 Nov 2007, 21:56
by Peet
Make your alpha as a greyscale bmp and then stick it into the alpha of the image with http://www.mnwright.btinternet.co.uk/do ... xtbmpx.EXE

Posted: 16 Nov 2007, 04:43
by rattle
It must've been Photoshops color management. Turned it off now... grrr.