Alpha Channel vs. Opacity Mask

samcole

Hello fellow artists! I was wondering what is the industry standard in regards to using either the alpha channel for transparency when creating a texture, or creating an opacity mask? In school we learn to utilize the alpha channel of a texture, but I was watching the Sci Fi Floor texturing video from 3D Motive and that artist uses an opacity mask with the RGB channels to set up his initial emissive, and transparencies.

I've also heard that the alpha channel creates another texture draw call on the game engine in order to render it, so its more resource intense. Any info to clear up the confusion would be great. Thanks guys.

Computron

Using the alpha is a way to avoid introducing another texture sample. But using this channel increases memory usage by 2 times. so you could us the channel or add one more texture sample and get two extra channels for the same memory size.

m4dcow

If I remember correctly he packs the opacity mask and the emmissive together. Remember a DXT5 (which supports a grayscale alpha) is twice the size of a DXT 1.
So 2 DXT1s is the same size as a DXT5 and you have 2 extra channels you can do something with. Since he has an opacity and emmissive channel it is worth it to store in an extra DXT1.

Computron

It really depends on the game and the engine. If your making a portfolio, don;t worry about it, just do what will survive compression better.

samcole

@m4dcow, yea he does pack the emissive, and opacity together. Most of my work will be for my portfolio. I graduate at the end of this spring this year.

@Computron, I'll keep that in mind. I wasn't really worried, its just I've seen two different methods to produce similar results and I just felt like asking which one may be the preferred method.

Ace-Angel

It's a fine balance, reason why it all depends up to you and what you're trying to accomplish for you asset.

Remember in a Porftfolio, you will be showing your maps, guys that hire you couldn't care less about where you packed what, since it's varies between developments and pipelines.

For example, many people keep their Gloss map inside Specular Map's Alpha channel, since the two complement each other (having different size Specular and Gloss isn't advisable due to Mip-Mapping around the borders which could lead to 'cuts' where the two materials don't correspond).

But at the same time, many people use the full RGBA set of channel, each channel = own mask, in the case of Emissive.

Unless you're really trying to make a nice looking game while still pulling the double and even triple digits in the frames, then alot can be forgiven.

samcole

So in the end, just make it look amazing for my portfolio, and the studio will help me learn their technical workflows after hiring. Thanks for indulging my questions everyone.