From the course: Digital Media Foundations

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Masking areas of the picture with chroma key and luma key

Masking areas of the picture with chroma key and luma key

From the course: Digital Media Foundations

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Masking areas of the picture with chroma key and luma key

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- [Instructor] The alpha channel for a pixel uses the same bit depth as the color channels. The numbers are the same, so it's fairly straightforward to translate one channel figure into another. You can designate areas that should be transparent manually using a mask, and when you do that you're using a shape to set an adjustment to just the alpha channel on the pixels selected. But you can also automatically apply adjustments to the alpha channel on pixels based on colors or luminance. Let's look at a simple example of this, lumakey. Put simply, when you lumakey pixels, you convert the luminance level of each pixel to its alpha channel. Unless you make any adjustments to the effects settings, only pixels that are perfectly black will be completely transparent, because only an alpha channel of zero is totally invisible. The brighter each pixel is, the more opaque it will be, until pixels are completely white and therefore completely opaque. Lumakey can produce some lovely effects, if…

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