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-   -   How to make an Alpha Channel with Photoshop (http://www.lucasforums.com/showthread.php?t=126716)

svösh 04-13-2004 06:18 AM

Alpha channels can be made quite easily if you know Photoshop, I will assume you don’t and try to explain this the most direct way.

Every time you make a selection ( ie marching ants you can go to the selection drop down and save the selection, this in essence will create your new alpha channel. Now It will be stark black and white no gray tones. An alpha channel is used in supported 3d programmes to mask off areas of your graphic, the intensity of black in the alpha channel will dictate how much of the original design that you see. Ex. Black will be 100% transparent and white will be 100% opaque keeping this in mind we will attempt to make your custom hilt shiny by using say a light tone (25% black or so) your original image will show through 75% and the other will be the gun metal or whatever .txi file your working with.

Behind the layers palette you will see two other tabs, one is channels and one is paths.
We will be focusing on the channels. The first thing you need is a layer that will be the hilt you can have as many layers as you would like but you need all the alpha information in one channel as you can only save tga.s with one alpha channel

Go ahead and Ctrl + left click your hilt’s layer’s thumbnail icon in the layer palette, ( the mini image of the actual layer) this will select only the opaque pixel information and not the transparent area. Ok now with the selection active go to the selection drop down and choose save selection. You have just made an alpha channel go to the channels pallet and check it out. You will see a white hilt area on a black backgroud. Ctrl + d to deselect anying that was selected Next we invert the alpha channel. Hit Ctrl+I to invert Still in the alpha channel palette just like the layer there are little eyes next to the thumbnails. This will turn on and of the channels, I want you to click the alpha on so your work space is only the alpha channel now at the top of the channels pallet you see rgb channel now turn it on and you will see a red semi transparent mask of the area that was black should show your graphic through. However this is just a preview of what we want

If you want softer edges you can either use the gaussian blur filter or select the black and go to the selection drop menu and choose feather selection. I would not exceed 2 pixels in this case . Remember apply this only to the alpha channel and not your original artwork.

Now turn off the rgb channel and
Go back on the alpha channel press w to get the magic wand tool and select the black areas that will be the main section of the hilt. Now go to you forground colour and make it light gray now hit g to get the paint bucket fill tool. Fill the selection and make it gray. Now after all that duplicate your document by right clicking the title bar of your document and choosing duplicate. Flatten the image layers > flatten image save this as ???.tga 32 bit make sure you have save with alpha channel check box on.

Make sure the file referred to in the .txi file is the same as your graphics name.

I really hope this helps you. Oh and if you want a really good example of complex alpha channels extract this PMBBL01.tga ( it’s the soldier’s default clothing.) it has shinny spots on the metal backpack notice the detail in the alpha channel.

svösh


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