Second Life Forums Archive - How do I copy an alpha channel?

Lee Ludd

Scripted doors & windows

Join date: 16 May 2005

Posts: 243

10-08-2005 08:25

I'm using Photoshop, latest version. It's driving me nuts.

I have two textures; let's call them Left and Right. Each texture has the three RGB channels and an alpha channel. Each is 256px wide and 512px high. I want to combine them into a single texture, 512px by 512px, with the Left texture occupying the left side, and the Right texture occupying the right.

I widen the canvas of Left to 512px x 512px, forcing the image to remain on the left side. Let's now call this image Both.

I try to copy Right to the right side of Both. The RGB channels come through fine. I can't get the Alpha channel to move over there.

How would an expert combine Left and Right to create Both?

Wisper Patel

Registered User

Join date: 22 May 2004

Posts: 66

10-08-2005 08:45

Just delete the original alpha channel and make a new one for your "new" image that has two sides now.

Lee Ludd

Scripted doors & windows

Join date: 16 May 2005

Posts: 243

10-08-2005 08:57

Thank you very much!

That did work.

I did have one minor problem. When I tried to copy the alpha channel from (say) Left to the left side of the new alpha channel of Both, I got some monochrome version of the entire left image, not just the alpha channel. I had to delete the RGB channels, and then make the copy. There must be some way to select ONLY the alpha channel that I haven't discovered. Do you know how?

Ben Bacon

Registered User

Join date: 14 Jul 2005

Posts: 809

drag-n-drop

10-08-2005 09:35

You can copy layers and channels from one document to another by positioning the target document so that you can see at least a part of it once you select the source document. Then just drag the layer or channel from the palette window to the target document window.

Robin Sojourner

Registered User

Join date: 16 Sep 2004

Posts: 1,080

10-08-2005 10:20

Yep, as Ben says, the easiest way to do this (IMHO) is to drag the layers and channels. It works like this.

1. Change Canvas Size for both documents, forcing the Right to stay on the Right, and the Left to stay on the Left, so you get two documents with the stuff on one side, and the other side empty.

2. Select all the layers of the Right document, hold down the Shift key, and drag them onto the Left document. (The Shift key will cause them to land in exactly the same place that they came from, assuming the documents are the same size.)

3. On the Right document, go to the Channels palette, hold down the Shift key, and drag the channel onto the Left document. (It's not necessary to change to the Channels palette on the Left document. Photoshop knows the difference between Layers and Channels, and won't mix them up, no matter what palette you have showing.) This will give you two Alpha Channels.

4. On the Left document, switch to the Channels palette, select the first Alpha channel, and then go to Select > Load Selection. Choose Alpha 2 as the selection to load.

5. Fill the selection with white, effectively transferring the information from the second Alpha channel onto the first.

6. Delete the second Alpha channel.

If you find the shift-drag too difficult to do, you can also just right click on the layers or channel (Control+click on a Mac with a one button mouse,) choose "Duplicate Layer" or "Duplicate Channel" from the menu, and then choose the other document as the one to duplicate into.

That will get the layers and channels into the other document without any worries about being slightly "off", if you have problems with the shift-drag, to replace steps 2 and 3. Step 1, and steps 4-6 will remain unchanged.

Hope this helps!

_____________________

Robin (Sojourner) Wood
www.robinwood.com

"Second Life ... is an Internet-based virtual world ... and a libertarian anarchy..." Wikipedia

Lee Ludd

Scripted doors & windows

Join date: 16 May 2005

Posts: 243

10-08-2005 11:25

Thank you, responders, for you careful answers to my question. It's a great help.

How do I copy an alpha channel?
Lee Ludd Scripted doors & windows Join date: 16 May 2005 Posts: 243	10-08-2005 08:25 I'm using Photoshop, latest version. It's driving me nuts. I have two textures; let's call them Left and Right. Each texture has the three RGB channels and an alpha channel. Each is 256px wide and 512px high. I want to combine them into a single texture, 512px by 512px, with the Left texture occupying the left side, and the Right texture occupying the right. I widen the canvas of Left to 512px x 512px, forcing the image to remain on the left side. Let's now call this image Both. I try to copy Right to the right side of Both. The RGB channels come through fine. I can't get the Alpha channel to move over there. How would an expert combine Left and Right to create Both?
Wisper Patel Registered User Join date: 22 May 2004 Posts: 66	10-08-2005 08:45 Just delete the original alpha channel and make a new one for your "new" image that has two sides now.
Lee Ludd Scripted doors & windows Join date: 16 May 2005 Posts: 243	10-08-2005 08:57 Thank you very much! That did work. I did have one minor problem. When I tried to copy the alpha channel from (say) Left to the left side of the new alpha channel of Both, I got some monochrome version of the entire left image, not just the alpha channel. I had to delete the RGB channels, and then make the copy. There must be some way to select ONLY the alpha channel that I haven't discovered. Do you know how?
Ben Bacon Registered User Join date: 14 Jul 2005 Posts: 809	drag-n-drop 10-08-2005 09:35 You can copy layers and channels from one document to another by positioning the target document so that you can see at least a part of it once you select the source document. Then just drag the layer or channel from the palette window to the target document window.
Robin Sojourner Registered User Join date: 16 Sep 2004 Posts: 1,080	10-08-2005 10:20 Yep, as Ben says, the easiest way to do this (IMHO) is to drag the layers and channels. It works like this. 1. Change Canvas Size for both documents, forcing the Right to stay on the Right, and the Left to stay on the Left, so you get two documents with the stuff on one side, and the other side empty. 2. Select all the layers of the Right document, hold down the Shift key, and drag them onto the Left document. (The Shift key will cause them to land in exactly the same place that they came from, assuming the documents are the same size.) 3. On the Right document, go to the Channels palette, hold down the Shift key, and drag the channel onto the Left document. (It's not necessary to change to the Channels palette on the Left document. Photoshop knows the difference between Layers and Channels, and won't mix them up, no matter what palette you have showing.) This will give you two Alpha Channels. 4. On the Left document, switch to the Channels palette, select the first Alpha channel, and then go to Select > Load Selection. Choose Alpha 2 as the selection to load. 5. Fill the selection with white, effectively transferring the information from the second Alpha channel onto the first. 6. Delete the second Alpha channel. If you find the shift-drag too difficult to do, you can also just right click on the layers or channel (Control+click on a Mac with a one button mouse,) choose "Duplicate Layer" or "Duplicate Channel" from the menu, and then choose the other document as the one to duplicate into. That will get the layers and channels into the other document without any worries about being slightly "off", if you have problems with the shift-drag, to replace steps 2 and 3. Step 1, and steps 4-6 will remain unchanged. Hope this helps! _____________________ Robin (Sojourner) Wood www.robinwood.com "Second Life ... is an Internet-based virtual world ... and a libertarian anarchy..." Wikipedia
Lee Ludd Scripted doors & windows Join date: 16 May 2005 Posts: 243	10-08-2005 11:25 Thank you, responders, for you careful answers to my question. It's a great help.

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How do I copy an alpha channel?