digitalFAQ.com Forum - How ColorMill filter for VirtualDub works

I have been spending a lot of time restoring some badly digitized 16mm film. I'm trying to wrap this up before I get to my VHS captures. In the process, I have been using AviSynth and VirtualDub tools I found here. I have gotten some very good results with the feedback I received on DF. I have mostly used various combinations of HDRagc with AviSynth and Color Mill, Gradation Curves, a touch of HSV Adjust, and judicious use of NEAT Video.

Some of Color Mill's operation was mysterious at first. Sanlyn's description in https://forum.videohelp.com/threads/...-as-VirtualDub helped get me started. I used another of Sanlyn's suggestions to use Color Tools 1.5 to pull up a histogram in VirtualDub. The information below is a description of what I saw the various Color Mill controls had on a RGB histogram. Some of these controls operated differently than what I expected.

Middle Point:
Middle Point slider expands/contracts values above black level. Positive values expand histogram above black. Negative values moves whole histogram left and crushes into black (level 0).

Booster slider acts as +/- fine tuner for Middle Point.

Base Shift slider moves slight peak of values in middle of video black to bright ends. Slider up moves peak toward bright end which seems to slightly darken shadows when I look at the actual image instead of the histogram. Slider down moves peak toward black end which seems to brighten shadows. Not sure of actual action.

HSV:
Hue slider shifts balance between all three colors.

Sat slider up expands red brightness and contracts green and blue levels. Slider down contracts red level and expands green and blue brightness. Not what I expected.

Value shifts all colors and luma toward/away from bright end. Width of each histogram remains constant.

Gamma:
Sliders up expand width of each color range until fully off black then width stops changing. Moving slider up further moves full level range as a whole. Sliders down will crush each color toward black.

Levels:
Dark slider moves black point for all colors. Mostly affects values below 128.

Middle slider proportionally expands/contracts all color’s width from 0. Does not crush histogram into black like Middle Point control does. But, it does tend to crush upper levels into bright end (255).

Light slider expands/contracts right side of histograms for all. Only affects values over 128.

Red-Green-Blue:
Dark: Slider adjusts black level for each color.

Middle: Slider expands/contracts width above black for each color. Black level does not change.

Light: Slider adjusts top brightness level for each color.

In closing I have found that different filters operate differently for what would seem to be the same function. For example, the Gamma action in Color Mill is different that the action in the Gamma Correction filter. The Gamma Correction filter increases/decreases the width of the histogram for each color in reference to the bright level (255) instead of the black level. Similarly, the HSV Adjust filter changes hue differently, and I think better, than the hue adjustment in Color Mill.