G RGB Colour Mixer
G RGB Colour Mixer is a new way of manipulating the colours and tones of an image without using look-up tables (LUTs). It is especially suitable for creating the look of old film processes as well as very subtle film effects. The filter is fully Y’CbCr even though it works with RGB, and also has the option of working in linear gamma, which can produce different and better results than working in the normal gamma of video which is around 0.45. However in the initial code for G RGB Colour Mixer, the linearisation of the gamma in FCP was being done using LUTs, and these were producing artifacts. I changed the linear gamma mode to use instead a close approximation to the linearisation which gives many of the benefits of working in linear gamma, but also imparts a beautifully subtle S-shaped curve onto the video's tonal look, enhancing this filter’s use for creating Film Effects.
The filter works in three parts, the Gamma Controls, the + Channel Mixer and Overall Controls:
The Gamma Controls offer a new way of tonally balancing an image. The general method is to increase the Bright Strength and Dark Strength to around 100 or so, and then adjust the Mid-Tone Point until the image looks balanced. For effect you can change the Bright / Dark Blending to harshen or soften the transition from dark to bright. To finally tweak the effect, change the Bright and Dark Strength and the other controls until you are happy.
+ Channel Mixer
The + Channel Mixer allows you to change the balance and composition of the Red, Green and Blue channels that make up the image. Normally these channels are kept separate, but with the mixer you can add in, say, the blue channel to the red by increasing the +Blue Mix in the +Red Properties section. You can also select from a number of presets so that you can get the feel of what kinds of effects can be created with this filter. The Brightness Balance control will adjust the relative brightness of the new Red, Green and Blue channels you have created to help you keep the effect producing the overall tonal look you want. By adjusting the Inter Channel Balance you can allow more or less of the effect to come through, and this will also aid in keeping the overall colour balance of the effect correct.