The Channel Combiner effect extracts, displays, and adjusts channel values for a layer.
This effect is one of the most interesting effects and it is hard to fully understand what it does.
Channel Combiner offers several distinctly different useful functions. One, it’s a great Channel shifter. You can move information between Color and Luminance channels. It’s particularly good at creating grayscale information from a color image. Secondly, sometimes it’s better to process your images in HSL or YUV color space. Channel Combiner can convert between those color spaces. Third, some effects have problems as processing images with alpha channel. Channel Combiner can convert between can straight and premultiplied alphas, making it easier for those effects to do their job.
It creates great greyscale images by taking one channel and converting it to a greyscale channel, such as luminance. You can take any channel from the image and make it a greyscale image solely off the information of one channel. You can also take the value of one channel and move it into another(such as taking the red channel and putting it into the green channel).
You can also create different color conversions through this. You can take an image from one color space and move it into another (RGB to HLS, etc.).
You can do other little games with the channels as well. Say you want to see the Red displayed strictly in red colors. Very easy to do. Let’s say we wanted to have the Red replace the Green channel to get strange colorization of your scene. Then there are other games you can play as well. Now what’s also interesting is that Channel Combiner can look at a second layer to provide this incoming channel information. If the layer is completely different, you get some very strange results.
What this is more useful for this is if you have a very special version of footage like a particular 3D render that shows, say, surface normals or if you are trying to get a key out of heavily treated footage before keying it and now you want to use that result as the alpha channel for an image. These are the things you can do with either Channel Combiner or effects such as Set Matte. Now that’s one set of uses for Channel Combiner. A different set of uses are for color space conversions such as RGB to Hue, Light, and Saturation, or to YUV.
An interesting thing that Channel Combiner can do is move information from one color space to another, then back to its original state using a duplicate, and having certain corrections done in between the layers.
This is a very powerful effect to use in a lot of applications. I would recommend the Lynda tutorial that I found here:http://www.provideocoalition.com/luma_processing/ As well as that post.
Use Second Layer: Retrieve values from Source Layer, which can be any layer in the composition.
From: Which values to use as input; the first several items in the menu are multichannel combinations of input and output options, so they don’t require you to set a To value. Saturation Multiplied uses the saturation value multiplied by the lightness value, where lightness is the minimum distance to black or white. For example, a dark or light blue pixel has a lower value than a bright or pure blue pixel. This option represents the most common view of the saturation value of a pixel. Min RGB uses the lowest value among the red, green, and blue channel values. Max RGB uses the highest value among the red, green, and blue channel values.
To: The channels to which to apply the values. Choose Red Only, Green Only, and Blue Only to apply the value to one channel only and set the other color channels to zero. Choose Alpha Only to apply the value to the alpha channel and set the color channels to 1.0. When you select Hue Only, the applied hue value is combined with 50% lightness and 100% saturation. When you select Lightness Only, the applied lightness value is combined with 0% saturation, which then gives the hue no influence. When you select Saturation Only, the applied saturation values are combined with 0% hue and 50% lightness.
Invert: Inverts (subtracts from 1.0) the output channel values.
Solid Alpha: Makes the alpha channel value 1.0 (complete opacity) throughout the layer.