| Tutorial 2 - Creating a basic alpha channel |
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| Written by FelixofMars | |||
| Wednesday, 07 July 2004 | |||
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It is most likely that a transparent texture will be used somewhere with a game. Even in todays climate where even more millions of polygons can be used there are occasions when alpha's still have there uses, for example, in racing games. Developers usually create flat polygon planes and map tree, bush or even animated crowds onto them. As you may or may not know all textures are rectangles, so to make the image appear not rectangle in shape the engine has to be told what not to render to the viewer. Artists use an alpha channel to tell the games engine render to anything white within the alpha map, ignoring anything coloured black. It is also possible for some engines to render things that are grey as opaque and even use how dark or light the grey is to make the texture more or less visible. This is also have some alternative use's with things like bump/normal mapping which is a way of telling the engine to render depth onto flat faces, but at this point we are looking at Alpha's only.
 If the texture was mapped to the model, as it is now, the texture would appear as a ships wheel, with a white background, which is not what is required. The artist must switch to the channels tab from the layers tool menu inside Photoshop. By clicking on create a new channel the artist is presented with a blank canvas, where the alpha channel must be painted. Switching back to the layers menu, so the original image appears, the artist begins selecting around the wheel, using the magic wand tool and in conjunction with other selection tools such as area. Switching back to the alpha channel the artist can simply fill the unwanted area of the image in black and the wanted area in white. The artist may spend some time cleaning up the alpha channel, using the pencil tool on the minimal brush size setting. The alpha channel in Photoshop should look something similar to the image displayed below. This image is then saved using a suitable format that supports alpha channels in most cases this will be *.tif for example.  To make the image appear as an alpha channel, when rendered, using 3D studio Max, and the artist must assign a texture in the usual way, using the material browser. Then clicking on the Go to Parent option, from the menu bar, the list below should show the maps option. By clicking on the maps option, a drop down list appears with new options on it. One of the options should be marked opacity, clicking on the tick box to activate it, then the button marked none opens the Material/Map browser. As with the texturing method described, earlier in the report, an image can be added by selecting the bitmap option. The image, below and to the left, helps to better illustrate how to perform these actions.
This done the opacity map has to be told to use the alpha channel to create the transparency. So the artist must click on the option marked Alpha from the mono channel output menu. The image, below, helps to show where the option is located. Note: New versions of Max tend to set the Alpha channel automaticlly, so you may not need to set this option and it may appeared disabled, In this case the above step can be ignored.  This is the basic knowledge you need to creating an alpha channel for a 3D model. Below is an example render of a Boat with the ships wheel Alpha applied to it, As I explained earlier you can make parts of the textures opaque by using grey within the alpha channel. I hope this example proved helpful to you.
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| Last Updated ( Thursday, 26 April 2007 ) | |||
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