You have an image on your screen, nothing magical at this time, except that it is made of pixels, the smallest part of data put screen. Pixel = Picture Element. Now in fact a pixel is a square that makes part of a matrix. A matrix is a square made of 64 pixels, 8 * 8. A matrix contains pixels on or off >> 1 or 0 They have 3 base values, RGB = Red Green Blue. A pixel beeing on or off makes the matrix have some shape this shape is a letter or digit, this makes text on screen Now using this matrix in another style, you can produce image values for many colors depending on its color depth. I will not start here the color depth and resolution tutorial i made 5 years ago, that will be for another tutorial. Well that was it long time ago. Now resolution and grafix cards have been accelerated and enhaced 1000 times, so what i said in intro is passed years ago. Let's see how works an alpha channel. An alpha channel doesn't exist untill you create it. You create it for parts from the image you decide. The intro is not put here randomly, it makes sense to put it here. Your picture has 3 base values beeing RGB. So your picture has 4 channels, beeing the main channel a mix of all channels, and the separated RGB channels. Now you can add as many other channels as you like, but these will be mixed down when the desired effects are reached. The alpha channel is one such channel, but this one is very special and will not be mixed down and will remain untouched. your texture needs some transparent or masked areas, so you've learned how to produce mask color in the index for PCX images for UED2. OK, whats so different on the alpha channel then ? Masked textures make some parts completely transparent as if they were inexistant, now the alpha channel does much more. Like the crosshair it uses white or grey parts to be semi translucent or opaq or completely transparent like mask textures. Black = complete see through Grey values = glass see through White = complete opaq. Your actual image contains wallbricks and a windowglass so you want the glass to be translucent but not the bricks. In photoshop, select only the parts of the glass to be translucent. then in menu > Window > select Show Channels another viewbox will show on the workdesk. This one will show Layers, Paths and Channels. Select the Channels tab. Now you see the channels i told you of previously Main and RGB channels. Don't touch the selected parts of the image,we're not done yet. In the channel viewer, look at its bottom and find some small icon representing a curled sheet, leftclick it and your new channel will be created. This one is called the Alpha channel be default and will be black also by default, meaning complete translucent by default. This allows you to make opaq or less the selected parts. Now fill the selected parts with white if you want them to be completely opaq or grey for translucense at some degree. You must understand that these saved pictures have some special format to work with alpha channels, and PCX does not allow this, so it wont work for UED2 but it will for UED3. Supported formats are TGA, DDS (DXT) DDS is very compressed and very high quality for UED3 more later on this compression. A DXT filter for photoshop and a preview DLL for windows explorer are available from NVidia corp at their home site. Aswell as the Bright compression tool for older UT engines. (higher image sizes than 256 reduced with quality to 256)