Usage guide for Compositing with Carbon Basic
Key Processing

This is the process of generating a key channel. The same process is used by all filters that require an image type key, and is the same for all key sources.

The first step when making a key from another element is to select the data from the key source of interest, this can be the red, green, blue, or alpha data. A new array of data is created by the resize and blur function, controlled by the resize value (center actual, follow, virtual, or full), the size of the target element, and the desired softness. This data is then scaled so that values within the clipping range fall within the Min and Max values. Values below Low Clip are set to Min value, and values above Hi Clip are set to Max. Key Invert simply swaps Min and Max during scaling.

If a pattern is used as the key it is created at the required size, there is no blurring or slope adjustment available for patterns.

The last stage replicates the data as needed for repeated keys.

The resize/blur function is seperate from the one used in blending. This resizer lacks the ability to deform or rotate (ie does not use a mesh) but does incorporate a fast blurring algorithm.

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