Page Comparison

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, materal material or even groups of objects and materials– defined on the scene and obtained during the full frame process.

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Center
Setting an extra sampling on render to refine only the skin areas. The armour and body looks clean at SL 10 (above) while the skin areas still need more rendering, mainly in the back-lit ears. Instead of continuing to refine the whole frame, you can use a mask of the skin areas (center) and get those areas rendered up to SL 18 (below). Image courtesy of Quentin Chaillet (www.qchaillet.com)

During the render 

During the first step of the render process, the engine is rendering the full frame as usual. The SL parameter indicates the global sampling level of the whole image as with any regular render. The Extra Sampling parameter aside displays n/a (not activated), indicating that the extra sampling has not started. (and indicates that the render is still operating in full frame mode).  

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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. 

If for any reason you need to homogenize an heterogeneous render, just resume it with a new sampling zone by simply inverting the original mask (with the Invert Mask option) to equalize the SL of the previous area. 

How does the Extra Sampling feature

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work? 

Take a look at how this feature works in this video overview. 

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