The top channels are the color channels and the optional Alpha channel. They are always organized in the same order and they cannot be erased. Selection masks are described below and displayed as a list in the dialog. Every channel appears in the list in form of a thumbnail. A right-click in a channel thumbnail opens the channel menu.

Every channel is shown in the list with its own attributes. The main attribute is the name of the channel itself. You can edit selection masks by double-clicking on their name. A double_click on the thumbnail opens a full dialog where you can also set the visual aspect of the channel in the image window. In front of the thumbnail there is an eye icon: by clicking on it you define whether the channel is visible or not. As a result of this visibility, the view of the image changes in the image window and a white image becomes yellow if you remove the view of the blue because yellow is the complementary color for blue. If you remove the view of the Alpha channel, everything becomes transparent and nothing else than a grey checkerboard is visible. The aspect of this virtual background can be changed in the Preferences. The chain icon enables grouping of channels for operations on multiple channels.

Caution

Activated channels appear highlighted in blue in the dialog. If you click on a channel in the list you toggle activation of the corresponding channel. Disabling a color channel red, blue, or green has severe consequencies. For instance if you disable the blue channel, all pixels from now on added to the image will not have blue component, and so a white pixel will have the yellow complementary color.

Under the channel list is a set of buttons allowing you to perform some basic operations on channel list.

Once the channel is initialized, selected (highlighted in blue), visible (eye-icon in the dialog), and displayed as you want (color and opacity attributes), you can start to work with all the paint tools. The colors used are important. If you paint with some color other than white, grey, or black, the color Value (luminosity) will be used to define a gray (medium, light, or dark). When your mask is painted, you can transform it to a selection by clicking on the Channel to selection button or from the context menu.

You can work in selection masks not only with the paint tool but also with other tools. For instance, you can use the selection tools to fill areas uniformly with gradients or patterns. By adding many selection masks in your list you can easily compose very complex selections. One can say that a selection mask is to a selection as a layer is to an image.

	Caution
	As long as a selection mask is activated you are working in the mask and not in the image. To work in the image you have to deactivate all selection masks. Don't forget also to stop displaying masks in the image by removing the eye icon. Check also that all RGB and Alpha channels are activated and displayed in the image.

To initialize a Quick Mask, click the bottom-left button in the image window. If a selection was active in your image, then its content appears unchanged while the border is covered by a tranlucent red color. If no selection was active then all the image is covered by a tranlucent red color. At every moment you can hide the maskby clicking on the eye icon in front of the QMask. From the channel dialog you can double click on the name or the thumbnail to edit the QMask attributes. Then you can changethe Opacity and its filling color. Once a quick mask is initialized click on it to be sure it is selected and blue highlighted in the list, and start to paint on it with any GIMP paint tool. The mask is coded in gray tones, so you must use white or gray to decrease the area limited by the mask and black to increase it. The area painted in light or dark gray will be transition areas for the selection like feathering. When your mask is ready, click again on the bottom-left button in the image window and the quick maskwill be removed from the channel list and converted to aselection. Quick mask's purpose is to paint a selection and its transitions with the paint tools without worrying about managing selection masks. It's a good way to isolate asubject in a picture because once the selection is made you only have to remove its content (or inverse if the subject is in the selection).

Description

	Screenshot of the image window with activated QuickMask. The QuickMask is filled with a gradient from black (left) to white (right).
	The QuickMask is now disabled and a selection is initialised from the QuickMask, which was filled by a gradient before. You see the selection borders in the middle of the image.
	A stroke is now added during the enabled selection. The key is, that the black color will have no opacity of the resulting stroke (right) and white color will have a full opacity of the stroke (left).

After the QuickMask Button is pressed, the command generates a temporary 8-bit (0-255) channel, on which the progressive selection work is stored. If a selection is already present the mask is initialized with the content of the selection. Once QuickMask has been activated, the image is covered by a red semi-transparent veil. This one representes the non-selected pixels. Any paint tool can be used to create the selection on the QuickMask. They should use only greyscale color, conforming the channel properties, white enabling to define the future selected place. The selection will be displayed as soon as the QuickMask will be toggled but its temporary channel will not be available anymore.

	Tip
	To save in a channel the selection done with the Quickmask select in the image menu Select/Save to Channel