Focal Blur Filter
Focal Blur filer mimics focal blur effect with ensemble samping in a fast way.
Most setting of focal blur filter (such as distance from camera to the focus) looks the settings in camera property.
Known problems: this filter do not works properly in fisheye or equirectangler rendering.
Quality
Higher value uses larger number of sampling point. Focal blur filter has two types (Simple and High Quality). "High Quality" algorithm gives better result at the sharp edge in depth buffer, but its speed is more slow and it requires higher quality value than that of simply way.
Gamma Correction
RGB value of pixels is averaged in bluring process. Since RGB value is non-linear, simple averaged values RGB are not the accurate averaging of brightness.
When this checkbox is on, this effect is cancelled by additional correction of gamma.
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