The image or document's color mode determines the number and type of color channels available to you. Each channel stores color information specific to it, which, when combined with other channels, brings about the full color image. For example, a red channel would store only red color information in RGB color mode.
Channel information is displayed in the Channels panel.
Color modes and channels
For each color mode, the following channels are available.
RGB: Red, Green, Blue channels
CMYK: Cyan, Magenta, Yellow, Black channels
Grayscale: Intensity channel
Lab: Lightness, AOpponent, BOpponent channels
Image and layer channels
The Channels panel always displays an image's channels when loaded. From an image channel you can:
Protect the channel from editing.
Hide the channel.
Create a spare channel (i.e., a saved selection) from any channel's information.
Store a new selection based on the channel information.
Add, subtract, or intersect a channel's selection to/from/with a previously made selection, respectively.
For any currently selected layer (pixel, mask, adjustment or live filter), the layer's channel(s) are displayed below the image channels. From each layer's channel you can:
Invert, clear, and fill the channel information.
Create a new grayscale layer.
Create a new mask layer.
Create a Spare Channel (i.e., a saved selection) from the channel information.
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.
Pixel selections and masks
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 color channels of the current layer blend with the underlying layer(s). For more information, see Layer blend ranges.
Editing spare channels
The spare channel that stores your mask can be isolated for editing. This lets you paint and erase directly on the spare channel, as well as apply filters such as Gaussian Blur for softer mask edges.
To hide/show image channels:
From the Channels panel, click Visible on the channel entry.
To protect image channels from editing:
From the Channels panel, click Editable on the channel entry. A grayed out icon means the channel is no longer editable.
To create a mask or grayscale layer from a current layer's channel:
-click the layer's channel, then click Create Mask Layer or Create Grayscale Layer.
The new layer is added to the Layers panel.
To invert, clear or fill a layer's channel:
-click the layer's channel, then click an option from the pop-up menu.
To save a selection as an alpha channel:
With a pixel selection in place, -click the 'Pixel Selection' entry and select Create Spare Channel.
The selection is stored at the bottom of the Channels panel as a new 'Spare Channel' entry.
To edit a spare channel and apply to a mask:
From the Layers panel, select a mask layer.
From the Channels panel, -click the Mask Alpha layer, and choose Create Spare Channel.
Click on the newly created 'Spare Channel' entry to isolate it.
Edit the spare channel.
Reselect the mask layer in the Layers panel to exit isolation mode.
-click the spare channel and choose Load to Mask Alpha to apply the edited spare channel to your mask.
Before editing a spare channel, you have the option of duplicating the initial spare channel. This procedure is often used to preserve an unedited backup copy of a spare channel before editing the original.
To duplicate a spare channel:
-click the 'Spare Channel' entry and select Duplicate.
The duplicate is stored below the original as a new 'Spare Channel' entry.
To rename a spare channel:
-click the 'Spare Channel' entry and select Rename.