We use the term "alpha texture" to refer to special texture maps that are partly made up of normal color pixels, and partly of special transparent pixels. Most texture images have three color channels, red, green, and blue. In an alpha texture, there is a fourth channel, the alpha channel, which defines the transparency of the image, pixel by pixel.
By using alpha textures, you can extend the range of effective graphic tricks you can perform with DesignWorkshop, especially for live walkthroughs and animations. Alpha textures are great for representing materials holes and/or complex outlines.
Alpha textures can be applied to geometry using mappings just like standard textures, tiling or full-face. A tiling alpha texture provides a good way to show a continuous material with lots of holes, like chain-link fencing. A full-face alpha texture is useful for showing a single image with complex edges, like a fully-detailed photographic tree.
An alpha texture can be created readily from a conventional solid texture image by adding a fourth channel to the image.
1) Start with a standard texture, from any source like an existing textures library, a scanned image, or digital photo. For example, see our standard texture making instructions.
2) Open the standard texture image file in Adobe Photoshop. The specific commands listed here are based on Photoshop 3.0, but the same concpets will aplly to later versions.
Use the Image menu Image Size command to make sure the image has a 'resolution' of 72 dpi. If it doesn't already, then reset the image 'resolution' so it is 72 dpi, keeping the 'file size' constant.
3) Using the various Photoshop selection tools, like the magic wand and Select Similar, for example, select all the areas of the image you want to eventually render as transparent.
4) Once you have these areas selected, use the Select menu Save Selection... command, and save the selection as a new, Untitled channel. This saved selection will be the basis for the alpha channel.
5) Next, create the actual alpha channel. Use the Window menu Palettes > Show Channels command to display the Channels floating window. At the bottom of the list of channels, there should be a new channel named "#4". Double-click on the name of channel #4, to open the Channel Options for it. In the Channel Options dialog box, change the name of the channel to 'Alpha', and make sure the Color Indicates: radio button is set to Masked Areas.
The solid colored area (or Masked Area) in the Alpha channel indicates the pixels which will be rendered solid in the alpha texture. If necessary, you can quickly flip the pixel value using Select All followed by the Image menu Invert command.
6) Now save the completed texture image in the PICT file format. Give the image a useful name, a color depth of 32 bits per pixel (for its four eight bit channels) and no compression.
You have now successfully created an alpha texture. To use it with default 2'x2' tiling, just drop the texture PICT file into the active Textures folder and then start up DesignWorkshop. Just apply the new texture to an object, and view your creation in Lights and Textures.