GamMac: a new Avisynth tool to remove color cast

[VideoFred]

Hello everybody,

When transfering film, we have to deal very often with color cast especially on older films.
I noticed that when we split the digital file in R, G and B and then set gamma for each channel the same, the color cast dissapears.

This was my basic idea:
http://forum.doom9.org/showthread.php?t=173683

And this guy made an Avisynth filter from it:
http://forum.doom9.org/showthread.php?t=173695

GamMac not only corrects color cast, it also corrects levels.

A few examples:

Red R8 Agfa:


Unnkown film, R8 blue cast:


from the same film:


Unnkown film, R8 red cast:


from the same film:


Unnkown film, R8 blue cast:


Fuji Single-8 film, green cast:


From the same film:


Again from the same film:


And finally Peruchrome Super-8, blue cast:


The GamMac filter runs nearly in real time.
Above examples are made almost without filter parameter tweaking.
The only thing I did was reducing the red adjustment a litte bit. (same adjustment for all examples)

This filter can also be used for photos.

many greetings,
Fred.

[RyanH]

Neat technique. Looks similar to some of the automatic curves adjustment tools in Photoshop. If so, watch for some odd results in edge cases where the original footage genuinely had little or no information in one or more of the colour channels. Examples would be shots of blue sky over blue water, or some winter scenes.

[milesandjules]

Looks great fred

[VideoFred]

Neat technique. Looks similar to some of the automatic curves adjustment tools in Photoshop. If so, watch for some odd results in edge cases where the original footage genuinely had little or no information in one or more of the colour channels. Examples would be shots of blue sky over blue water, or some winter scenes.

This is true and that's why R,G and B can be fine tuned. But in 80% of the cases it gives remarkable good results, with only some minor Red adjustment. The needed amount of correction depends on the film brand itself of cource but also on the used capture system. (Light source and camera.) I have done many tests with my own capture system but also with files from the Filmfabriek scanner. But GamMac will work with any source. Even with very bad VHS tape and scans from old photos.

These are old 1970's photos:
On this one, I had to do some secondary color (blue hue) corrections.


This one needed no additional color corrections.



Fred.

[Will2]

That's basically what I do in DaVinci Resolve with the color wheels...make the RGB parade scope line up. Good technique and is more objective than just "eyeballing" it.