ArtMatic TechNotes
Alpha Channel Confusion
Alpha Channels and ArtMatic
If you open an image created by ArtMatic in another application, like Preview, and it looks different than it did in ArtMatic, it is likely that you inadvertently created a tree with an alpha channel without intending to. An alpha channel is an invisible picture layer that defines the transparency of the visible (Red, Green, Blue) layers of the picture.
This tree has a 4-output tile at the bottom. The fourth output is coming from a tile that has no impact on the RGB layers of the picture. As a result, the alpha channel gives the image a surprising appearance when it is opened in an application that uses the alpha channel.
When an ArtMatic tree has a four-output tile at the bottom, ArtMatic will create a picture that has 3 color layers (Red, Green and Blue) PLUS an alpha channel that is defined by the fourth output. Unless you have intentionally done something to make the alpha channel visible in ArtMatic, the alpha channel will have no effect when you are in ArtMatic. (This is because an alpha channel only means something when the image is being combined with another image. Applications like Preview assume that if there is an alpha channel that you intend to have your image be transparent where the alpha channel indicates and so they combine your image with a solid color background.)
Alpha channels (also called transparency masks or alpha masks) are very useful when compositing images together especially for creating video effects. But, if one creates an alpha channel image accidentally, it can have an adverse effect.
If you did not design your tree with the intention of having an alpha channel, there are three solutions:
- Put a 3->3 component at the bottom of the tree to "block" the alpha channel so that ArtMatic renders images without the alpha channel.
- Or, leave your ArtMatic files alone and remove the alpha channel from the rendered images using PhotoShop or Graphic Converter or any other application that can strip out the unwanted alpha channel.
- Or, re-design your tree to eliminate the unwanted alpha channel. This is probably the best choice but requires that you have a pretty good understanding of how your tree works.
This tree has an added 3->3 tile that prevents the alpha channel from being rendered.
For this tree, this is probably the best solution. The tile that fed thefourth output of the original tree had no other function than creating the alpha channel. So, removing it speeds up the tree rendering and nothing is lost since it was not used by the visible layers of the image.
If you are intentionally creating an alpha channel, it is often helpful to add a component to the tree to help you visualize the alpha channel as shown in the tree below. See the 4->4 chapter of the Component Reference for information about components useful for visualizing alpha channels.
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