View Full Version : Alpha layer

08 August 2004, 05:23 PM
I am working on a character in Softimage XSI 4.0. While I was trying to begin on the texture I heard some good things about an “Alpha layer”. Can someone explain to me what the function is of an Alpha layer and how I can put it on?


08 August 2004, 05:04 AM
I`m on xsi 3.51. Is there a node called alpha layer in 4? or are you talking about an alpha channel used to composite shaders ?? I would describe what an alpha does and how to (extract them) use them in the render tree, but maybe too obvious and probably not what you`re asking for. ???

08 August 2004, 09:51 AM
I thought it is a second layer or something with texturing. I have never textured before so I don't know a thing about it. I can also use the wrong name for it.

On thing forum you see it quite often, one layer with colors and stuff and one layer for the texture of the skin, I think/guess.

But if that is true my question is also, why not using one skin.

08 August 2004, 10:17 AM
Combine your two images (or proceedurals) with a "mix2colours" mixer node, one in Base Colour and one in Colour1, then use either a grey scale image (or proceedural) in the Weight slot to act as an alpha channel.
On the weight (alpha) map, white will let the base colour to show through, black will show the Colour1 slot, shades of grey will be a combination of both.

08 August 2004, 08:24 PM
Besides the info yog gave you remember that you may have an image with an alpha channel ( RGB + alpha ) made in photoshop for example, and you may want to use that image alfa so you can have a yellow phong material and on top of it you have an image or logo ( for example) with it's alpha, in that case You need to extract the alpha so you can use it in the weight input of your mix2colors. To extract the alpha use the "color channel/ picker" node ( it is already set by default to extract the Alpha channel), you can also use any gradient or greyscale matte image to act as the weight, but if you make your image with alpha then you need to extract it, since there is no "use alpha" option. Here's a screen cap so you see what I mean:

Hope this helps.
P.S. you can have several textures to place in one head for example and each with a different projection and they can mix together with this method it is a bit easier if the image has an alpha channel since you know exactlly where it will be placed and will use the same texture projection as the image (rgb).

08 August 2004, 04:32 PM
thanks a lot, I will show the result later

08 August 2004, 08:08 PM
...but if you make your image with alpha then you need to extract it, since there is no "use alpha"'s called.. 'multiply weight with alpha'... or you can simply use the 'alpha' blending mode... no need to pick up the alpha.

you can also use my mix8layers.. that comes with some more alpha options.. it's on highend3D>maya>shaders.


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