2.6. Fuzzy Selection (Magic wand)

2.6. Fuzzy Selection (Magic wand)
	2. Nástroje pro výběr

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

Při používání kouzelné hůlky je velmi důležité dobře zvolit správný počáteční bod. Pokud zvolíte špatně, může být výsledek úplně jiný, než si představujete.

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.

Povšimněte si, že jak se vybraná oblast rozšiřuje směrem od počátku, nešíří se jen po pixelech, které se skutečně dotýkají, ale je schopna překonávat malé mezery. Vzdálenost, kterou může výběr přeskočit, lze nastavit dialogu Předvolby v části Volby nástrojů : Implicitní práh. Zvýšením hodnoty můžete hůlku učinit agresivnější. (Nastavení se projeví i u Plechovky.)

2.6.1. Activating the Tool

There are different possibilities to activate the tool:

From the main menu: Tools → Selection Tools → Fuzzy Select.
By clicking the tool icon in the Toolbox.
By pressing the U keyboard shortcut.

2.6.2. Key modifiers (Defaults)

Kouzelná hůlka nemá žádné zvláštní modifikační klávesy, pouze ty, které ovlivňují všechny nástroje pro výběr stejným způsobem. Více se o nich dozvíte v kapitole Nástroje pro výběr.

2.6.3. Tool handling

Obrázek 14.19. 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. Options

Obrázek 14.20. 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 Windows → Dockable Windows → Tool Options which opens the option window of the selected tool.

	Poznámka
	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.

Hledání podobných barev

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

Zvolit průhledné oblasti

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.

Ukázka sloučení

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

Obrázek 14.21. Example for Diagonal Neighbors

A pixel with 4 orthogonal neighbors

A pixel with 4 diagonal neighbors

A pixel with 8 neighbors

Obrázek 14.22. Example for Diagonal Neighbors option applied

Diagonal Neighbors option unchecked

Diagonal Neighbors option checked

Práh

Tento posuvník určuje rozsah barev, které budou vybrány, v momentě, kdy kliknete na počáteční bod a ještě netáhnete myší. Čím vyšší práh, tím větší výběr. Po prvním stisknutí tlačítka myši se tažením dolů nebo doprava dá velikost výběru zvyšovat. Tažením doleva nebo nahoru pak zmenšovat. Proto, bez ohledu na nastavení prahu, máte vždy stejné možnosti – liší se pouze to, jak moc musíte táhnout myší a na kterou stranu, abyste dosáhli požadovaného výsledku.

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.

Obrázek 14.23. Example for Draw mask option applied

Fuzzy Select used with Draw Mask option unchecked

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