2.8. Foreground Select

Figure 13.29. The Foreground Select tool in the Toolbox

The Foreground Select tool in the Toolbox

This tool lets you extract the foreground from the active layer or from a selection. It is based on the SIOX method (Simple Interactive Object Extraction). You can visit its Web page at [SIOX].

2.8.1. Directions for use

The creation of a selection with this tool works in a couple of steps:

  1. Roughly select the foreground you want to extract. When you select this tool, the mouse pointer goes with the lasso icon. It actually works like the Fuzzy Select tool. Select as little as possible from the background.

    As soon as you release the mouse button, the non selected part of the image is covered with a dark blue mask. If the selection is not closed, its ends will be linked automatically together by a straight line. The mouse pointer goes now with the Paint-brush icon for the next step.

    Figure 13.30. The foreground is roughly selected

    The foreground is roughly selected

  2. Draw a line through the foreground: using the paintbrush, whose size can be changed in options, draw a continuous line in the selected foreground going over colors which will be kept for the extraction. The color used to draw the line is of no importance; not using the same color as foreground is better. Be careful not painting background pixels.

    Figure 13.31. The line drawn on the foreground

    The line drawn on the foreground

    In this example, it is important that the line goes over the yellow capitulum of the flower.

  3. When you release the mouse button, all non-selected areas are in dark:

    Figure 13.32. The area which will be selected

    The area which will be selected

  4. You still have to press the Enter key to get the wanted selection:

    Figure 13.33. Foreground is selected

    Foreground is selected

[Note] Note

Until you press Enter, you can't undo this selection by Ctrl+Z nor by SelectNone, and the Undo History is not concerned. To delete this selection, you must select another tool.

2.8.2. Activating the Tool

You can activate the Foreground Select tool in two ways:

  • by clicking on the tool icon in the Toolbox,

  • through ToolsSelection ToolsForeground Select in the image menu.

  • This tool has no shortcut, but you can set one using EditPreferencesInterfaceConfigure Keyboard ShortcutsToolsForeground Select

2.8.3. Key modifiers (Defaults)


By pressing the Ctrl key, you can switching between foreground and background selection painting.

2.8.4. Options

Figure 13.34. Foreground Select tool options

Foreground Select tool options

Normally, tool options are displayed in a window attached under the Toolbox as soon as you activate a tool. If they are not, you can access them from the image menu bar through WindowsDockable WindowsTool Options which opens the option window of the selected tool.

Mode; Antialiasing; Feather edges
[Note] Note

See Selection Tools for help with options that are common to all these tools. Only options that are specific to this tool are explained here.


If this option is enabled, only the area contiguous to the stroke will be selected. Otherwise all the areas with same colors will be selected.

Figure 13.35. Contiguous option effect

Contiguous option effect

Two separated areas with the same color. On the left, only the left area is marked.

Contiguous option effect

The Contiguous option is checked: only the area close to the painted line is selected.

Contiguous option effect

The Contiguous option is not checked: both areas, although they are separated, are selected.

Interactive refinement

Here are some options to work more precisely on your selection:

Mark foreground

default option. The foreground color of the Toolbox is used to paint. Colors covered by the painted line will be used for extraction.

Mark background

You can access this option either by clicking on the radio button or, more simply, by pressing the Ctrl key. The mouse pointer goes with a small eraser icon. The used color is the background color of Toolbox. The pixels of the selection which have the same color as the erased pixels will NOT be extracted.

Small brush / Large brush

This slider lets you adapt the size of the brush used to paint the line. A small brush fits well thin details.


The slider lets you remove small holes in your selection.

Figure 13.36. Smoothing option effect

Smoothing option effect

For this demonstration, small holes painted with the background color of the image have been added (left).

Smoothing option effect

Smoothing = 0 : more than 1 pixel wide holes are not selected.

Smoothing option effect

Smoothing = 7 : less than 3 pixels wide holes are selected.

Preview color

You can select between Red, Green and Blue to mask the image background.

Color Sensitivity

This option uses the L*a*b color model. If your image contains many pixels of the same color in different tones, you can increase the sensibility of the selection for this color.