Effects » Colour » Technical » Quick video levels


Quick video levels
Author(s):
Release date: May 3, 2018
Creation date: May 18, 2017
License: unknown

Lightworks user effect QuickLevels.fx

This is a quick video level adjustment tool, similar in many respects to the colour
correction effects supplied with Lightworks. It differs in that hue and vibrance
adjustments have been added. There is also a master amount adjustment to give more
control of the effect. Individual colorimetry controls aren't available because
that isn't the purpose of this tool.

The parameters are:

Amount : Allows the grade to be faded in or out.
Gamma / Exposure : Adjusts the image gamma.
Brightness : As used in LW colour correction.
Contrast : As used in LW colour correction.
Gain : As used in LW colour correction.
Hue : Trims the hue by plus or minus 90 degrees.
Saturation : Increases or reduces master saturation.
Vibrance : Allows mid range saturation to be enhanced.

The gamma parameter differs from Lightworks practice because I wanted it to feel
more like an exposure adjustment, hence the name. Reducing the gamma darkens the
image, the reverse lightens it. The Brightness, Contrast and Gain parameters on
the other hand behave in exactly the same way that they do in Lightworks' colour
correction effects. The code to implement them is pretty standard, so that isn't
too surprising.

Hue adjusts the hue through plus or minus 90 degrees, and saturation over the hue
range remains constant. The range covered by Saturation is from zero (black and
white) to 200% saturation. Adjustment is based on video luminance and not on an RGB
average, which differs from the Lightworks algorithm.

Vibrance matches the Photoshop effect of the same name quite closely, and has been
implemented from a widely published algorithm. At the extreme ends of its adjustment
range it differs a little from the Photoshop version. Whether that's due to the
algorithm or this implementation of it is unclear, but it has been assessed to be
near enough for the purpose.
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