I seam to struggle understanding Alpha Channels

ArtWilliams · (#1)

Hello,

I am starting to learn about matte painting, having great fun with it and wanting to get my teeth stuck in really with it all.

My friend is fantastic with 3d work and he was explaining to me about Alpha channels with matte painting.

But I dont really get how to do it for my work.

For instance, if I have a layered project of mountains, each row lets say has its transparent sky. But when I go to save my work I cant choose save as alpha channels in photoshop.

Sorry if this is a stupid question I dont know where to begin :s

Thanks

nickmarshallvfx · (#2)

I'll try and help you out here, hopefully this will make sense:

So basically, an alpha channel is just a greyscale image that is used to represent transparency. Not all softwares have the same interpretation, but in Photoshop, black is fully transparent and white is fully opaque. The various shades of grey between black and white become different degrees of semi-transparent. Sometimes you have to invert your alpha as some softwares will assume white as transparent and black as opaque.

Some image formats can hold this greyscale alpha image as well as the regular rgb image that you are saving out. This means that if you need to maintain transparency information for use in a 3d package, you have all that information in the image.

So how do you create on in photoshop? There are a few ways, but probably the easiest is to load the element as a selection, go into the channels tab, and create a new channel. In this new channel, fill the selection with white. This will maintain semi transparency too. When you save out now, you file will have an alpha, providing you are using a format that can hold alpha information. The most common of these are:
.tif, .tga, .exr, and i think .png and a couple of others. A quick google search will tell you all of them if you need them.

Hope it helps.
Nick

ArtWilliams · (#3)

EDIT: I have figured out alpha channels now, thank you very much for your help! I really appreciate it!

nickmarshallvfx · (#4)

No problem, glad to be of service :)