Following is the manual steps to unmultiply an image in Photoshop the hard way:
Let's say you have a cloud with transparency for example.
- Have the original painted (or not more likely these days) cloud with transparency in Photoshop open.
- If you have a layer mask, delete it, an apply it.
- Ctrl (PC) or Command (MAC) click on the layer to select the layer's transparency.
- Save the channel as an alpha. Make sure it's the only alpha.
- Now duplicate the cloud layer with transparency once. Take the duplicated layer and merge down (ctrl or command e). That's 2 cloud layers merged. Duplicate that and merge. You have 4. Duplicate that and merge. You have 8. Duplicate that and merge. You have 16. Duplicate that and merge. You have 32. Duplicate that and merge. You have 64. Duplicate that and merge. You have 128. Duplicate that and merge. You have 256. Duplicate that and merge. You have 512. Duplicate that and merge. You have 1024. Duplicate that and merge. You have 2048. Duplicate that and merge. You have 4096. Good enough. The power of 2. Gotta love it. I suggest you make a Photoshop Action for easier future use.
- Now I suggest you add a layer below the cloud layer and make it a general sky color, or the average color of the actual cloud's background. If you've truly unmultiplied the cloud it wouldn't matter what color you made the background. Pink, black, white, or green. It just gives you more peace of mind that it's goint to cut out of that color. Some Artists use whatever the background was. That's a waste of disk space. But it can be useful for reference when lining up in 3D.
- Now flatten or merge the rgba image. You have an unmultiplied cloud texture for Maya / Mental Ray. Use .tga for mental ray. Unless they fixed it. Used to be mental ray didn't support .lzw .tif's. Annoying. .tga works for maya or mental ray rendering.
Side note. After Effects can view and save unmultiplied images. Shift click on alpha in comp window. Very convenient. Wouldn't you think that the After Effects team and Photoshop team at Adobe could have lunch one day and share that code? PHOTOSHOP NEEDS TO BE ABLE TO VIEW AND SAVE IMAGE(S) UNMULTIPLIED. THOMAS KNOLL, JOHN KNOLL, HELLO! Not ranting, just trying to get the word out. Write them! Put on your blog(s). Photoshop should just do this out of the box.
Enjoy,
Louis Katz
www.louiskatz.com
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1 comment:
I'm not sure I follow when you say "shift click on alpha in comp window" for AE.
Also, coming from the AE world, Unmultiply means you want to create transparency from a layer that has none.
Usually, that's a Lens Flare on a black solid. It doesn't have any transparency, so you use unmult to create an alpha channel for that layer.
Your technique just does the reverse.
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