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Old 07-26-2014, 01:01 AM   #1
Sairus
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Default Reconstructing a Missing Blue Channel

Greetings,

I've been extracting art assets from games and have recently come across a crop of large images that were missing their blue channels. I'd never seen this before, but some checking into it revealed that it's a pretty clever way of saving texture space. From what I understand you only store three channels (Red, Green and Alpha) then use those three to extrapolate the Blue. (At least I think that's what it does)

The Unreal Dev Kit apparently relies on this a lot : http://oliverm-h.blogspot.jp/2013/05...e-channel.html

So what I'm asking is how can I take this file with it's missing Blue channel and repair it in Photoshop?

Here's a sample of the texture file: http://speedy.sh/F5me2/Atriumtest.psd

I've been trying to think of some way of combining the 2 RG channels and comparing them against the complete Alpha channel to create the B, but I haven't figured out the correct way to do this.
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Last edited by Sairus : 07-26-2014 at 01:26 AM.
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Old 07-26-2014, 02:43 AM   #2
muzz
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Actually the blue channel in most normal maps is not actually used, it's not nessecary.

However, your example image is not a normal map and i have no idea why you would have an image like that, what could cause you to loose a blue channel on an image?

Anyhow it seems your blue channel is where your alpha channel is.

I fixed it by ctrl clicking on the thumbnail which makes a selection based on value then ctrl+backspace on the blue channel to transfer the data. If it is inverted press ctrl+I to invert the channel.

However the colours still look wrong.

I really need to know what the final image is supposed to be if i were to do this properly :/.

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Old 07-26-2014, 02:54 AM   #3
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GOT IT!

So what has actually happened is the channels were all jumbled up.

I can probably make you a photoshop action to automatically fix them if you want?
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Old 07-26-2014, 03:00 AM   #4
Sairus
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Yup, I just realized that:
A) I gave you no source image to know what it was supposed to look like
B) Yes, the channels were just all jumbled up! I've already made an action to unjumble them, but thanks for looking into this and the offer!

I really need to start posting in this place more than just for asking for random help ever few months. Y'all are good people.
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Old 07-26-2014, 03:03 AM   #5
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Awesome!

I thoroughly enjoyed your little puzzle .

And yes you should.

I think a lot more of us are going to be making a big effort to get a bit more life in this place.
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