alpha textures in documentation

Refering to this documentation on “How do I Import Alpha Textures?”

[link text][1]
[1]: +http://docs.unity3d.com/Documentation/Manual/HOWTO-alphamaps.html

I have several questions…

why run dilate many times? what is the use of it? it makes the picture in no.5 become ugly than the original one.

From no. 6, Create a solid color layer at the bottom of your image stack. This should match the general color of your document (in this case, greenish). Note that without this layer Unity will take alpha from merged transparency of all layers. I not really understand this. Can someone explain how to do it and give some brief explaination?

Hello,

I don’t own Photoshop, but I can try to explain why you need to dilate your image :

When you have part of an image transparent, usually, the real color of the transparent pixels is white. You might think, the color of the transparent parts doesn’t matter, since they are transparent !

It matters because usually you use a filtering on the texture, meaning the color of the pixels will be mixed together to produce the color on the screen. If the color of the transparent pixels is white, you will get an ugly white border. The process of dilating the image is used to fix this. This makes the image “ugly”, but that doesn’t matter since this area is transparent anyway.