What is highlight clamping?

Highlight clamping has been introduced in post-1.3 versions of Corona. It clamps all samples before they are written into the frame buffer to the specified maximum value. This can help reduce noise, get rid of fireflies, and improve anti-aliasing around bright light edges at the cost of bias. Setting this value too low will result in visibly clamped highlights. Setting the value to 0 results in unbiased, highest-quality output.

You can find Highlight clamping in Render Setup > System > Frame Buffer > Image filter. The default value is 0.


Examples


1. Clamping = 0 (default value)
No highlight clamping occurs. Bright highlights and "jagged" edges are visible (lamp leg).
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2. Clamping = 1
Very low value causes visible highlight clamping which makes the image unrealistic. Note that no "jagged" edges are visible on the lamp leg.
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3. Clamping = 2
Clamping is still visible. No jagged edges visible.
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4. Clamping = 4
Clamping is still visible, but its level is acceptable. No jagged edges visible.
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5. Clamping = 8
There is almost no difference between this and the default (0) value, although the jagged edges have been reduced.
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