color correction video

Most videos need some sort of color correction. Not even sure why. The two main ffmpeg filters are colorbalance and colorchannelmixer.

Don't forget the basic splitting and recombining commands.

colorbalance

The easiest. 9 inputs, no alpha. 3 for each color (RGB). Within each color are (similar to GiMP) shadows, midtones, highlights. So... not too bad. The opposite of Red is Cyan, opposite Green is Magenta, and opposite Blue is Yellow. You can call a thing directly, but I always do all 9.

Zero does nothing. So any of these would do nothing. I like to be in the habit of using quotes, since quotes are used with multiple filters.

$ ffmpeg -i foo.mp4 -vf colorbalance=0:0:0:0:0:0:0:0:0 unchanged.mp4

$ ffmpeg -i foo.mp4 -vf "colorbalance=0:0:0:0:0:0:0:0:0" unchanged.mp4

$ ffmpeg -i foo.mp4 -filter_complex "colorbalance=0:0:0:0:0:0:0:0:0" unchanged.mp4

$ ffmpeg -i foo.mp4 -vf colorbalance=rs=0 unchanged.mp4

The last one illustrates what's in each of the 9 positions. We can call them by RGB name or position... rs:gs:bs:rm:gm:bm:rh:gh:bh: or positions 1-9. A common one on crappy online downloads is blown out red and blue which requires both a color correction call and a saturation call.

process

The settings are very sensitive, typically a person will make changes less than 0.1. Take a screenshot from the video, open GiMP and correct it till you get it right in GiMP, then just mimic the settings in colorbalance.

A typical, fairly strong, correction might be...

$ ffmpeg -i foo.mp4 -vf colorbalance=0:0:0:-.1:0:-.1:0:0:0 rednblue.mp4

....or even less...

$ ffmpeg -i foo.mp4 -vf colorbalance=0:0:0:-0.05:0:0:0:0:0 redmild.mp4

I could have done this last one with...

$ ffmpeg -i foo.mp4 -vf colorbalance=rm=-0.05 redmild.mp4

time-saving

GiMP with a screenshot. Otherwise, start with reds, go to blues, then greens. Getting the reds correct is key, then blues to give a little yellow, and then finally will need to remove some green

gamma

About the time the colors are right, it might be too dark. That's common. I lighten it back up.

$ ffmpeg -i foo.mp4 -vf "colorbalance=-0.03:-0.05:-0.1:-0.05:-0.05:-0.1:0:0:0","eq=gamma=1.2:saturation=0.9" correct.mp4

Once I had a very minimal one...

$ ffmpeg -i foo.mp4 -vf "colorbalance=0:0:-0.03:0:0:-0.05:0:0:0","eq=gamma=1.2:saturation=0.9" correct.mp4