2.8. Forgrunnsutval

Figur 14.34. Symbolet for «forgrunnutsvalet» i verktøyskassa

Symbolet for «forgrunnutsvalet» i verktøyskassa

This tool lets you extract the foreground from the active layer or from a selection. With GIMP-2.10, selection refinement has been improved. After the selection is made, with its marching ants, you can copy-paste or click-and-drag it to another image used as background,and, inverting the selection, you can can make changes in background.

2.8.1. Aktivering

Du kan aktivere dette verktøyet på to måtar:

  • ved å klikke på verktøysymbolet i verktøykassa

  • eller frå biletmenyen via VerktøyUtvalsverktøyaForgrunnutsval.

  • Dette verktøyet har ingen snarveg, men du kan lage ein ved å gå inn på FilBrukarinnstillingarGrensesnittSet opp tastatursnarvegarVerktøyForgrunnsutval

2.8.2. Bruksmåtar

Let us start with an object distinctly different from background, not needing to be refined.

  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 Free Select tool. Select as little as possible from the background.

    When the mouse pointer comes over line beginning, a small yellow circle appears: release mouse button to close selection. While selecting, click-and-drag draws a fuzzy line, drag only draws a straight line.

    If the mouse pointer doesn't cover start point, double clicking closes selection with a straight line.

    The selection is closed.

    As soon you click to start drawing, a small window pops up:

    For the moment, only a little cross is active, allowing to quit: returns to the original image.

  2. Press Enter to create the mask:

    The mouse pointer goes now with the Paint-brush icon. The dark blue area (this color can be changed) is for background. The light blue area covers the zone you have selected, on which you will paint to extract foreground. It contains the foreground area and a small part of background. Outside the selected area, the dark blue area is named Unknown pixels area.

    Options in the small window become active:

    • A Preview mask checkbox that toggles displaying a preview of the foreground extraction status.

    • A Select button that will be used to create the extraction after marking the foreground.

  3. Bruk penselen og trekk ein kontinuerleg strek over dei fargane du vil ha med i utvalet innføre markeringa. Du kan endre breidda på penselen etter behov. Det er likegyldig kva farge du brukar, men sjølvsagt er det lurt å bruke andre fargar enn dei du finn i utvalet. Det er viktig at du ikkje teiknar over nokre av bakgrunnsfargane.

    With this one-color object distinctly different from background, a few strokes are enough:

  4. Toggle preview to verify result.

    [Notat] Notat

    This Preview mask is a mask: you can draw directly on it and see result immediately.

  5. Try Matting Levin engine that may improve result.

  6. When you are satisfied with result, click on Select button to get the selection of the foreground with its marching ants.

2.8.3. Innstillingar

Figur 14.35. Innstillingane for verktøyet «forgrunnsutval»

Innstillingane for verktøyet «forgrunnsutval»

Normalt blir innstillingane for det valde verktøyet vist under verktøykassa. Dersom dette ikkje er tilfelle, kan du få tilgang til dei frå biletmenyen via VindaugeDialogvindaugeVerktøyinnstillingar som vil opne verktøyinnstillingane for det aktive verktøyet.

Mode; Feather edges
[Notat] Notat

Mange av innstillingane er meir eller mindre felles for alle utvalsverktøya, og er nærare omtalte i Del 2.1.2, “Innstillingar”. Berre innstillingar som er spesifikke for dette verktøyet er omtalte her.

Draw mode

Draw foreground: to draw what will be foreground.

Draw background: to draw what will be background.

Draw unknown: to add to your selection pixels that are in background.

Stroke width

The size of the brush.

Preview mask

You can adapt the color of the preview to your image.

Engine

Work with Matting global(default) and improve result with Matting Levin.

Iterations

Default is 1. Repeating algorithm may improve result.

2.8.4. Refining Foreground Extraction

In most images, foreground is not distinctly different from background. Refining selection allows you now to extract these foregrounds. Procedure steps are the same as above, but, during drawing foreground, you will often toggle Preview, use Zoom (+ key), Draw background to delete unwanted background extraction areas. You can also work directly on Preview mask.

Figur 14.36. Example for Draw background

Example for Draw background

On the left: drawing foreground ill-advisedly went over background area: a part of background will be included in foreground selection!

In middle: Draw background option is checked: draw on inclusion and unwanted pixels.

On the right: unwanted selected pixels in background are no longer in foreground selection.


Figur 14.37. Example for Draw unknown

Example for Draw unknown

On the left: the selection left a small part of foreground unselected, in unknown pixels area.

On the right: with Draw unknown option checked, draw on unselected pixels. They are now selected.