Alpha Channels Can Be Tremendously Powerful
An Alpha channel can be tremendously powerful when dealing with complex scenes or special effects.
For instance, the image rendering placed in front of a blurred background of a forest scene.
The forest is one layer in Photoshop that has had the Gaussian Blur filter (Filter>Blur>Gaussian Blur) applied to it.
The woman was "picked out" of her original rendering by using the Magic Wand tool to select the white pixels of the alpha channel, copy the colored pixels within that selection, and then paste them in a new layer over the forest.
By simply using the alpha channel to pick the woman out of the rendering, there was no need for time-intensive Photoshop work.
In the case of an animation where you are working with 30 frames per second, alpha channels are necessary when compositing computer-generated elements with other computer-generated clips or real-life footage.
Some important caveats about alpha channels to remember: • Thischannels create an alpha outline around everything in the scene.
Therefore, if you have floors or skies in the rendering, the alpha channel will include those, making it impossible to superimpose any characters over another scene.
If you plan to use compositing techniques to blend objects into other backgrounds, leave all "scenic" items (floors, skies, etc.
) out of the scene.
• Most special channels are pre-multiplied.
The basic gist of the problem here is that if you are anti-aliasing your render, you may end up with a black outline around the alpha-channeled image.
This is caused by both the color and that special channels being multiplied previously, and their addition leaves a black line.
If this occurs, use a straight alpha.
Straight alphas rid you of those annoying black halos.
But beware, if you are not going to composite a straight alfa-ed rendering, it is completely useless.
For instance, the image rendering placed in front of a blurred background of a forest scene.
The forest is one layer in Photoshop that has had the Gaussian Blur filter (Filter>Blur>Gaussian Blur) applied to it.
The woman was "picked out" of her original rendering by using the Magic Wand tool to select the white pixels of the alpha channel, copy the colored pixels within that selection, and then paste them in a new layer over the forest.
By simply using the alpha channel to pick the woman out of the rendering, there was no need for time-intensive Photoshop work.
In the case of an animation where you are working with 30 frames per second, alpha channels are necessary when compositing computer-generated elements with other computer-generated clips or real-life footage.
Some important caveats about alpha channels to remember: • Thischannels create an alpha outline around everything in the scene.
Therefore, if you have floors or skies in the rendering, the alpha channel will include those, making it impossible to superimpose any characters over another scene.
If you plan to use compositing techniques to blend objects into other backgrounds, leave all "scenic" items (floors, skies, etc.
) out of the scene.
• Most special channels are pre-multiplied.
The basic gist of the problem here is that if you are anti-aliasing your render, you may end up with a black outline around the alpha-channeled image.
This is caused by both the color and that special channels being multiplied previously, and their addition leaves a black line.
If this occurs, use a straight alpha.
Straight alphas rid you of those annoying black halos.
But beware, if you are not going to composite a straight alfa-ed rendering, it is completely useless.