The Channels panel lets you view and edit the image in separate channels. Channels are halftone images providing information about the brightness of color components. The channel list contains a composite image, color mode channels (RGB, CMYK, Lab, Grayscale), the transparency channel of the current raster layer (alpha channel), current selection channel, and the active layer mask channel. Each channel in the palette corresponds to a thumbnail image that displays all changes made to this channel.
You can adjust the size of thumbnails by clicking the button at the top of the Channels panel.
The active (editable) channel is highlighted with a dark gray background in the list. To select another channel, click on its name. When selecting a single channel, the image is shown as grayscale.
The visibility icon next to the inactive channel means that this channel is shown in the Image Window but is not editable. If several channels are visible, the image is displayed in color.
If you select the composite channel, all component channels become visible and active. The composite image is always located at the top of the list and is selected by default.
To edit a channel, use the usual drawing tools. Painting on a channel with white results in 100% intensity of the corresponding color. Different shades of color result in varying color intensity. The black color completely removes a color channel.
In the Alpha channel, by default, opaque areas are shown in white, transparent areas in black, and semitransparent areas in gray.
You can adjust the view mode for the alpha channel in the pop-up menu: Grayscale, Trimap, or Highlighted in Red.
Right-click on the alpha channel to open the context menu with the following commands:
Clear Alpha Channel fills the alpha channel with white, and the layer has no transparent areas;
Add Alpha Channel to Selection combines the alpha channel with the selection or creates a selection from the alpha channel;
Subtract Alpha Channel from Selection removes the alpha channel from the selection channel;
Intersect Alpha Channel with Selection creates an intersection of the alpha channel and the selection channel.
The Mask channel displays the current layer mask, if available: black marks protected areas, white marks unprotected areas, gray marks the transition zone. The mask channel has 6 view modes.
Right-click on the mask channel to open the context menu with the following commands:
Remove Mask deletes the current layer mask;
Apply Mask merges the mask with the layer;
Add Mask to Selection adds the unprotected area of the chosen mask to the selection;
Subtract Mask from Selection removes the unprotected area of the chosen mask from the selection;
Intersect Mask with Selection creates a selection that includes common parts of the selection and the unprotected mask area.
The Selection channel indicates the area of the current selection: white marks selected areas, black marks unselected areas, gray marks the transition zone. For this channel, 6 view modes are available.
Right-click on the selection channel to open the context menu with the following commands:
Deselect cancels the selection;
Invert reverses the selection;
Reveal Selection adds a mask which hides everything but selected parts of the layer;
Hide Selection adds a mask hiding the selected area.
You can change the displaying of contents of the alpha, mask, and selection channels in the Image Window by clicking the icon to the right of the channel's name and choosing from the options:
- Highlighted in Red,
- Inverted Red,
- Black Background,
- White Background.