Help on Creating an Alpha Channel

I have been trying really hard to understand how to create an alpha channel, but I must admit i'm really lost. I even have a photo shop book for dummies and it's not helping. lol

If anyone knows how to create an alpha channel, could you please explain to me what is the real purpose for them and also post a STEP by STEP tutorial or instructions on how to create one? Again, Thank you for all of your help.

Brianna

Hi Brianna!

The real purpose for alpha maps is to create transparent areas. Anything that is 100% black in the Alpha map will be 100% transparent in Second Life. Anything that is 100% white will be opaque, and shades of gray will be partially transparent.

I assume, from your post, that you are using Photoshop. If that's the case, I have a video tutorial showing how to make an Alpha map on my site here.

If I'm mistaken, and you are using PSP, Cristiano Midnight has one, too. You can find out about it in this thread.

If you still have questions after watching those, don't hesitate to ask!

As an addendum for the poor GIMP users around here, you can also just right click a Layer in the "Layers" tab and "Add Layer Mask" from there. Short and simple.

Also note that anything with alpha must be imported to Second Life as a TARGA (.tga) file. These files succumb to a few special render bugs in Second Life, but in general should be fine.

Here ya go:

Color Theory & Channels
Images designed to be shown on a color screen are comprised three colors (red, green, & blue). The relative brightness of each of these primary colors in each pixel determines each pixel's actual color. For example, a pixel comprised of equal values of red and blue without any green would appear to be purple.

When taken seperately, the individual values for red, green, or blue are represented by a grayscale image called a channel. In an individual channel, white represents the maximum possible concentration of color and black represents the absense of color. Shades of gray represent amounts of color that are less than the maximum. The darker the gray, the lesser the concentration of color. The lighter the gray, the more color is present.

Channels & Transparency (Alpha Channels)
Images that have transparency have the same three primary color channels and also have a fourth channel, called Alpha, which represents opacity. In the alpha channel, white represents comlete opacity and black represents the absense of opacity (transparency). Shades of gray represent semi-transparency. The darker the gray, the more transparent. The lighter the gray, the more opaque.

So, for example, if you are making a bikini top for your avatar, the alpha channel would be white in the shape of the bikini top, and black everywhere else. The white part makes the bikini top 100% opaque so that you won't be able to see through it when it's on the av, and the black part makes the rest of the image invisible so that there appears to be nothing on the av's arms, stomach, etc.

How to Create an Alpha Channel
Let's stick with the example of a bikini top.

1. On the Layers Palette turn off all layers except for the layer that has your bikini on it. (To turn a layer off, click the eyeball symbol to the left of its name.)

2. If the bikini layer has any white space around the bikini itself, use the eraser to get rid of the white space. It's very important at this stage that the bikini be on its own layer with nothing else on it.

3. On the Layers Palette, ctrl-click the icon for the layer with the bikini on it. (The icon is the little picture of the layer directly to the left of the layer's name.) This will select everything on the layer. You should see the "marching ants" outlining your bikini now.

4. On the Layers Palette, click the tab that says Channels to switch it to the Channels Palette. What you should see listed here are the three primary channels for your image, labled, "Red", "Green", & "Blue", and a master channel for the three, labelled "RGB". If you see any other channels besides those four, delete them now.

5. In the lower right corner of the Palette Window, locate the button that looks like a square sticker being peeled from its backing. It's the second one from the right. It's immediately to the left of the one that looks like a trash can. It says "New Channel" when you hover your mouse over it. Click it.

6. You should now see a new layer called "Alpha 1", which is currently all black. Make sure all channels except for Alpha 1 are turned off and that Alpha 1 is turned on. This should have happened automatically when you created Alpha 1, but if it didn't, do it now.

7. Your canvas should now appear to be solid black with the exception that you should still be able to see the "marching ants" outline of your bikini. Paint everything inside the outline white and leave everything outside of it black.

8. Click "Select" on the menu bar at the top of the screen to pull down the Select Menu. Click "Deselect" and you should see the marching ants disappear.

9. On the Channels Palette, trun the red, green, & blue channels back on, and turn Alpha 1 off. Now click the tab that says layers to switch back to the Layers Palette. Create a new layer by pressing the same button you previously used to create the new channel. (Just as it created a new channel while you were on the Channels Palette, it will create a new layer while you're on the Layers Palette.) Click on the name of this new layer and drag it underneath the layer with the bikini on it. Paint the new layer 50% gray or darker; black is fine. (The gray/black layer will prevent the white halo sometimes caused when Alphas are created the way we just did it. If you don't know what I mean by that, don't worry about. Just make sure to always put a gray/black layer underneath your work and you'll never have to see that white halo.)

10. Save your file as a 32-bit TGA and upload it to SL.

Enjoy.