Channel filters let you control the color and alpha channels of clips in your sequence to create a variety of visual effects.
Arithmetic blends a specific color channel of your clip with another color. From pop-up menus , you can choose the operator used and the channel it's applied to. The Color control changes the color with which the channel interacts .
Channel Blur allows you to apply different amounts of blur to a selected color and/or alpha channel of your clip independently. Sliders control how much blur is applied to each channel. Channel blurs create interesting color effects. The rack focus effect mentioned in the Gaussian Blur filter description can be taken to another level by garbage matting a subject onto a second layer and blurring one layer while unblurring the other layer.
Channel Offset offsets the position of one or all of a clip's channels within the frame. You can indicate the channel to be affected from the Channel pop-up menu. The Center Offset allows you to decide the amount and direction of the offset. You can select an edge from the Edges pop-up menu. You can animate this filter (using keyframes) and create some interesting effects. This might be great for a music video or for creating red/green 3D offsets.
Color Offset offsets the color of individual channels in the clip. Using this filter, you can create posterizing style effects. You've seen these; they look sort of like cartoons made from a live-action shot. Animating this filter reminds me of a Peter Max poster in motion; Yellow Submarine comes to mind. Sliders control the offset value for each color channel in your clip. You can either invert the image or wrap the colors. Experimentation is the key. Keep in mind that you can add more filters to really distort things. This one's fun.
Compound Arithmetic performs a composite between the first clip (the one you add it to) and one selected from the Browser and dragged to a well in the filter's settings. Several wells are available in other effects too; they all function similarly. To use them, just drag an image or clip to the well and release the mouse button there. You can adjust the operator (the way a composite is performed) and the channel it is performed on from two pop-up menus in the effect's controls. The well uses only the first frame of a video clip if it's put into the well. You can use stills to select the frame from video, or use a graphic image.
Invert inverts selectable channels of the selected clip. The result is like a negative image. The Channel pop-up menu lets you select which channel or channels to invert, and the Amount slider determines the amount of the inversion.