The image or document's colour mode determines the number and type of colour channels available to you. Each channel stores colour information specific to it, which, when combined with other channels, brings about the full colour image. For example, a red channel would store only red colour information in RGB colour mode.
Channel information is displayed in the Channels panel.
For each colour mode, the following channels are available:
The Channels panel always displays an image's channels when loaded. From an image channel you can:
For any currently selected layer (pixel, mask, adjustment or live filter), the layer's channel(s) are displayed in the bottom part of the panel. From each layer's channel you can:
The Channels panel also displays the alpha channel for the whole image or currently selected pixel, mask, adjustment, or live filter layer. These channels store transparency information, so it's a great place for more advanced masking control.
Another great use of alpha channels is the ability to store more complex selections that would otherwise be difficult or time consuming to recreate again. The Channels panel reports your current pixel selection as a channel entry, so by creating a 'new' Spare Channel from that pixel selection you've stored the selection for future use.
Because alpha channels store both selection and masks, the Channels panel acts as a great central point for working between masks and selections.
You can control how specific colour channels of the current layer blend with the underlying layer(s). For more information, see Layer blend ranges.