tif rgba alphachanne applied as transp.

M
Posted By
mingo
Jun 15, 2004
Views
478
Replies
7
Status
Closed
hi
we switched from v.7 to CS. and now also work with 16bit footage (mostly rendered within 3dstudio max). the fileformat of the output is 16bit RGBA (A stands for the alphachannnel)TIF uncompressed.

and here is my question/problem:
when i was opening a tif image in V7.0 the Alphachannel was sotred in a seperate Channel(so i could apply it later to layer0/background layer). In the CS version it is applied directly to the background without a mask and without a Alpha channel, so i loose the original background.
Also i did not find a setting turning off this behavior . A workaround, opening in V7 and then storing as PSD and then opening in CS works fine but is not so handy.
So:
Are there settings to turn off this behavior?
Is there a option to make the original Background visible again ,-something like unapply the tranparencay mask.
Would appreciate your help/comments
mingo
Related Tags
apply tiff

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CC
Chris_Cox
Jun 15, 2004
The behavior hasn’t changed from 7 to CS — if the TIFF file says the channel is associated alpha (transparency) then it is opened as transparency, and if it says it is unassociated (random alpha) then it is opened as an alpha channel.

No, there are no settings – this is part of the TIFF file format specification.
DJ
dennis_johnson
Jun 16, 2004
Mingo, you can create an alpha channel from the transparency information in your file using PS CS. Try Select/Load Selection, then Save Selection. This will allow you to save the transparency selection as an Alpha channel.
It’s a kludge, but whattaya gonna do?

(You may be able to find settings in 3DS Max that will allow you to save your TIFF differently – in the format that Chris suggests.)
M
mingo
Jun 16, 2004
M
mingo
Jun 16, 2004
thanx for your replies,
maye the behavior has not changed, but the same Tiff 16bit is treated differtly from 7 to CS, 7 stores it as alpha CS applies the as transp.

Dennis,
Yes i can create a alphachannel from the layertransparency (of course) but the original background is lost,
— think if a house rendered against a sky in 3dsmax, i want to do different operations with the foreground and the background, like masked adjustments, retouching etc…, therefore i need the alpha as a basis, but i would also like to have the original image and not only the foreground.

Of course we have workarounds like keeping 2 images one for the image one for the alpha would work but this causes waste of storage/time. Also converting with 7 would work.
we have to deal with this issue very often so a more
handy method would be nice.

for 3dsmax/mentalray there is no extra setting how to output the alpha

so
– is there a method/tool to tweak the alpha associaton?
– can you change the alpha association manually
– for CS it would be nice to have seperate channels not applied but treated as a seperate layermasks
DJ
dennis_johnson
Jun 16, 2004
I agree with you Mingo – I was just offering a possible solution. It’s true your "background" information is thrown out by PS/CS as it displays the image. At the studio we find sort of the opposite problem. Creating a transparency mask in Photoshop does not automatically create an RGBA file – it is necessary to promote the transparency to an Alpha channel before the file is useable in other applications, such as Shake.

It seems Adobe is more interested in being "right" than being useful.
M
mingo
Jun 16, 2004
yep,
the attitude to treat the alpha "correctly" also alpplies for the winxp explorer thumbs where the alpha imageparts are displayed in a white color.

— i just did a research how tiffs are stored but i did not find any tags in the header how alphas should be treated.
CC
Chris_Cox
Jun 16, 2004
Dennis – that depends on the file format. If the format supports transparency, then Photoshop saves (and reads) transparency. If the format doesn’t support transparency, then Photoshop cannot save or read transparency. Ditto for alpha channels.

Yes, we need to be right – when the file format says it works one way, we need to work that way. Not working that way creates more problems.

The only time this is a problem is when other applications fail to follow the specification for file formats.

Mingo – in the TIFF6 spec, look at associated versus unassociated alpha channels.

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