2.6. Fuzzy Selection (Magic wand)

图 14.23. Fuzzy Select tool icon in the Toolbox

Fuzzy Select tool icon in the Toolbox

The Fuzzy Select tool is designed to select areas of the current layer or image based on color similarity.

When using this tool, it is very important to pick the right starting point. If you select the wrong spot, you might get something very different from what you want, or even the opposite.

Fuzzy Select is a good tool for selecting objects with sharp edges. It is fun to use, so beginners often start out using it a lot. You will probably find, however, that the more you use it, the more frustrated you become with the difficulty of selecting exactly what you want, no more, no less. More experienced users find that the Path and Color Select tools are often more efficient, and use the Fuzzy Select tool less. Still, it is useful for selecting an area within a contour, or touching up imperfect selections. It often works very well for selecting a solid-colored (or nearly solid-colored) background area.

Note that as the selected area expands outward from the center, it does not only propagate to pixels that touch each other: it is capable of jumping over small gaps, depending on Threshold option. To increase/decrease Threshold, during the use of Fuzzy Selection, after the first button-press, dragging the pointer downward (or to the right) or upward (or to the left).

2.6.1. Activating the Tool

There are different possibilities to activate the tool:

  • From the main menu: ToolsSelection ToolsFuzzy Select.

  • By clicking the tool icon in the Toolbox.

  • By pressing the U keyboard shortcut.

2.6.2. Key modifiers (Defaults)

The Fuzzy Select tool does not have any special key modifiers, only the ones that affect all selection tools in the same way. See 第 2.1 节 “Common Features” for help with these.

2.6.3. Tool handling

图 14.24.  Using the Fuzzy Select tool: selected pixels are contiguous

Using the Fuzzy Select tool: selected pixels are contiguous

It starts selecting when you click at a spot in the image, and expands outwards like water flooding low-lying areas, selecting contiguous pixels whose colors are similar to the starting pixel. You can control the threshold of similarity by dragging the mouse downward or to the right: the farther you drag it, the larger you get the selected region. And you can reduce the selection by dragging upwards or to the left.

You can move the selection outline using Alt + arrow keys.

2.6.4. 选项

图 14.25. Tool Options for the Fuzzy Select tool

Tool Options for the Fuzzy Select tool

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 main menu through WindowsDockable WindowsTool Options which opens the option window of the selected tool.

[注意] 注意

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

Mode; Antialiasing; Feather edges

Common select options.

寻找相近的颜色

These options affect the way Fuzzy Select expands the selection out from the initial point.

Select Transparent Areas

This option gives Fuzzy Select the ability to select areas that are completely transparent. If this option is not checked, transparent areas will never be included in the selection.

Sample Merged

This option becomes relevant when you have several layers in your image, and the active layer is either semi-transparent or is set to another Layer Mode than Normal. If this is the case, the colors present in the layer will be different from the colors in the composite image. If the Sample Merged option is unchecked, the Fuzzy Selection will only react to the color in the active layer when it creates a selection. If it is checked it will react to the composite color of all visible layers. For further information, see the glossary entry Sample Merged.

Diagonal Neighbors

When activated, the tool considers diagonally neighboring pixels as connected when calculating the affected area. In other words, instead of looking at the four orthogonal neighbors of each pixel, it looks at all eight pixels

图 14.26. Example for Diagonal Neighbors

Example for Diagonal Neighbors

A pixel with 4 orthogonal neighbors

Example for Diagonal Neighbors

A pixel with 4 diagonal neighbors

Example for Diagonal Neighbors

A pixel with 8 neighbors


图 14.27. Example for Diagonal Neighbors option applied

Example for Diagonal Neighbors option applied

Diagonal Neighbors option unchecked

Example for Diagonal Neighbors option applied

Diagonal Neighbors option checked


阈值

This slider determines the range of colors that will be selected at the moment you click the pointer on the initial point, before dragging it: the higher the threshold, the larger the resulting selection. After the first button-press, dragging the pointer downward or to the right will increase the size of the selection; dragging upward or to the left will decrease it. Thus, you have the same set of possibilities regardless of the Threshold setting: what differs is the amount of dragging you have to do to get the result you want.

Select by

This option determines which component of the image GIMP uses to calculate the similarity in color.

You can choose from Composite, Red, Green, Blue, HSV Hue, HSV Saturation, HSV Value. LCh Lightness, LCh Chroma, LCh Hue, and Alpha.

Draw Mask

This option can help to visualize the selection. Selected areas marked with marching ants may not be evident when selecting with Fuzzy Select. If this option is checked, selected areas will be filled with a magenta color as long as you keep pressing on the left mouse button, and this mask will disappear as soon as you release this button.

图 14.28. Example for Draw mask option applied

Example for Draw mask option applied

Fuzzy Select used with Draw Mask option unchecked

Example for Draw mask option applied

Fuzzy Select used with Draw Mask option checked, left mouse button not released yet.