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Custom Alpha Channels Query

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Hi Pylon,

I started rendering with custom alpha channel set as below (SL max at 4, Custom Alpha set a t max 25).

But as the render progresses I've noticed that once the SL has reached it's max of 4 and when the Extra Sampling kicks in, the SL continues (albeit slower) to rise.

I've attached some snapshots to illustrate this. Surely if the SL level is rising, that means resources are taken away from the Extra Sampling computation?







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Hi Des,


As I understand it, the SL display value during Extra Sampling is an average of all the pixels' sampling levels in the scene, so the SL display value will increase as Extra Sampling proceeds. Maybe think of the displayed SL value as "Image average SL."  See A note on Sampling Level for heterogeneous renders.


On another note, if you are using the Custom Alpha as a mask, it is recommended that you set the SL to a minimum of around 6, so the alpha generated for extra sampling is not too grainy. If you'd prefer not to render the 'base' image to that SL, you can always generate a clean alpha for your glass beforehand, and then use the "Bitmap" option to specify the mask.



Does this help?

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