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View Full Version : OpenEXR... where is the alpha??



LW_Will
05-30-2009, 02:50 PM
Gentle people...

I tried to render to OpenEXRFP for output. Now, the files do not seem to have an alpha? Wasn't that correct? It should have an alpha right?

Why doesn't it? And what should I have done to make it save that alpha?

And yes, I know that the EXRTrader would work with this, just trying to see if that gets us closer to the goal. Thanks.

MooseDog
05-30-2009, 03:43 PM
have you tried openexr_rgbafp? *if* i'm right, the a stands for alpha.

Scazzino
05-30-2009, 03:47 PM
Right. The RGBA versions include the Alpha. If you are opening them in Photoshop CS4 though, it bashes the alpha into the transparency of the current layer. Is that what you are seeing? I use the older Photoshop CS with the EXRFormat plugin instead which preserves the alpha as a separate channel when doing stills and Apple Shake for animations.

toby
05-30-2009, 03:49 PM
have you tried openexr_rgbafp? *if* i'm right, the a stands for alpha.
Yes, RGBFP, without the A, won't save an alpha. Use the RGBAFP or RGBAHALF option. (HALF will be a smaller file size but store fewer buffers, which we don't have yet anyway, afaik)

Scazzino
05-30-2009, 04:01 PM
I think the half option is half the precision... ie 16 bit rather than 32 bit... but I don't recall where I saw that...

Lightwolf
05-30-2009, 04:21 PM
I think the half option is half the precision... ie 16 bit rather than 32 bit... but I don't recall where I saw that...
Yup, it is. Both as float though (HDRI).

Cheers,
Mike

LW_Will
05-30-2009, 10:55 PM
okay... ::bonk:: feeling very stupid right now.

Um... why would ILM make a format WITHOUT an Alpha? No, really, I want to know... ;-)

And yes, the HALF is Half the accuracy of the output... 16 as opposed to 32bits on the color. I think that the lower will work.

Thanks guys! You were great...

toby
05-30-2009, 10:57 PM
Um... why would ILM make a format WITHOUT an Alpha? No, really, I want to know... ;-)
I think that's a LW thing -

Red_Oddity
05-31-2009, 04:00 AM
The specs of the format don't state that an EXR file should contain RGBA data at all for that matter, it is specified that it can contain one or more image channels, which a program interprets by the given name of the image channel, some of these name strings have been predefined though (these being R for Red, G for Green, B for Blue and A for Alpha.)

That is just one of the small examples as of why EXR is such an incredibly flexible format.

Lightwolf
05-31-2009, 04:58 AM
The specs of the format don't state that an EXR file should contain RGBA data at all for that matter, it is specified that it can contain one or more image channels, which a program interprets by the given name of the image channel, some of these name strings have been predefined though (these being R for Red, G for Green, B for Blue and A for Alpha.)
Yup, precisely- quoted for agreement.

Cheers,
Mike

LW_Will
05-31-2009, 02:32 PM
yeah, EXR is a cool format.

I was looking at the specs and they used film terms to define how reactive the curve was (shoulder and toe). This is a film format adapted to the computer.

I find it troubling that the channels are undefined, but it makes sense. It is simply uses whatever you need for the channel format, and even other things that they did not think of at the time. I really like exr!

Is there a bit of definition for the channels in the exr file? There should be.

LW_Will
05-31-2009, 02:34 PM
I think that's a LW thing -

Isn't it always? :)

Lightwolf
05-31-2009, 02:58 PM
Is there a bit of definition for the channels in the exr file? There should be.
What do you mean? There is a certain semi-standard for the channel naming (for anything beyond RGBA and YUV)... but it's most useful if the reading app actually allows the user to choose where to load certain channels (Nuke does that extremely well).

Cheers,
Mike