Making an Alpha Channel

Making an Alpha Channel

This tutorial will help Photoshop users make an alpha channel for whatever purpose they might.

They are used for transparency and specular (shinyness).

First, open your texture your making the alpha channel in and go to the Channels tab.
Now, press the New Channel button and press OK to create a new channel.

Your image should now look like this.

Now you draw your alpha channel. You can't use any color in this. Black is clear (or flat) and white is opaque (or shiny).

When you're done drawing it, save it as a .DDS with the following settings.

And poof! You're done!

If you're using a bundledmesh, and want transparency, you'll need to name your material in 3DSMax:

<name>\_Alpha

If you have a staticmesh and want transparency, you'll need to name your material in 3DSMax:

alphatest\_<name>

If you add an alpha to a colormap in a bundlemesh it controls the specularity (shinyness).

Good info. I have some additional help for this subject. This method describes how to make a quick and dirty specular map for use in more than just transparency. This will produce usable results with zero additional effort, however there isn't a case in history where there wasn't a ton of room for additional work. It's up to you how far you want to take it.

Duplicate your flattened layer and remove the color[CNTRL/SHIFT/U]

Select->ColorRange and pick a neutral grey. Try 100 or 200 for the fuzzy. 200 retains more details, yet is not as contrasted.

You will be left with a selection that should look like this

Click the "Add New Channel" on the bottom of the channel pallete. You're done at this point if you want.

This shows the alpha with selection range of 200 fuzzy

What's left after this is to isolate areas and reduce/increase the contrast to suit the particular material. Metals are shiney, so more white. Plastics, fur, cloth are more diffused, so more black. Use Cntrl-I with selections to invert the shinyness.

Warning: This method takes into account ALL color information in your image. If there are elements which should not be defined in the alpha for transparency or lighting, then they should be removed before you sample the layer. Think of a picture within a poster. The paper has the details, not the ink that perfectly follows the paper. Showing highlights or edges(in a normal map) on the actual image in the poster will make it look like embossed plastic and really ugly.

Guywithawrench, on Nov 17 2006, 04:15 AM, said:
Every time i do create new channel it still is all black even after i have this selection.

Select>save selection>replace channel (overwrite the alpha). Use contrast/brightness on the selected alpha channel to get midtones.

Static meshs do not support semi-transparency. You're limited to using DXT1 (1bit alpha) textures for handling simple knockouts with their shader. As its 1-bit, the pixel is either there or its not - nothing inbetween like you would have with a DXT5 texture. Quality isnt so good, but its okay for wire fences and the like. For semi transparency, you'll have to use a Bundled mesh where DXT5s are ok to use. Note that you wont be able to lightmap whatever it is your working on. This should be ok for windows, but just be warned in advance thats the tradeoff.