Image courtesy of Quentin Chaillet (www.qchaillet.com)
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- Bitmap, feed with an existing black and white mask in any image format, manually painted or, more frequently, generated from an external channel export.
- Alpha, use the scene Alpha channel obtained during the full frame process.
- Custom Alpha, use any Custom Alpha channel –from object, material or even groups of objects and materials– defined on the scene and obtained during the full frame process.
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When a render contains areas with different Sampling Levels, generally the full frame is rendered to a certain SL, and then some areas are rendered to a higher SL– so the global SL value for the image as a whole is calculated by considering all the pixels in the image and their corresponding sampling values. That is the reason why on heterogeneous renders, the global SL is usually a decimal value (like 14.63) instead of the typical round numbers on homogeneous renders (like 14.00), where all the pixels present the same sampling value.
Bear in mind that if an a heterogeneous render is later resumed to a higher SL without indicating zones –full frame treatment–, all the pixels of the image will start to render until the average global SL reaches the new desired value. It will not homogenize the image, but will add samples to all areas.
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