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Part 1: About Channels Part 2: Extracting the Channels Part 3: Adjusting Opacity Part 4: Conclusion |
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Part
1: About Channels When an image is displayed on a computer monitor, each pixel in the image consists of three phosphorous dots: one red dot, one green dot, and one blue dot. As such, images are generally stored such that each pixel in the image is represented by three values for the three dots, each generally ranging from 0 to 255. The idea of channels is that the colour information from either the red, the green, or the blue dots can be extracted and worked with separately from the other coloured dots. If we work just with the red dots, we say we are working with the red channel.  Figure 1: Separating an image into its component channels. When an image is converted to black and white, typically what happens is that some formula is applied to each of the red, green, and blue values to come up with a single greyscale value, essentially throwing away the colour information. We are going to take advantage of how Photoshop lets us work with individual colour channels to better control this conversion process.
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