This is a non-linear contrast change useful for photo adjustments; it preserves highlight and shadow detail.
The midpoint is the midpoint of contrast. It must be in the range [0, 1], typically 0.5.
The factor indicates how much to increase or decrease the contrast, typically in the range [-10, 10] where 0 has no effect. A positive value increases contrast, while a negative value decrease contrast.
Usage #
Create the filter:
{{ $filter := images.Sigmoid 0.6 -4 }}