3. Snarmaske

Figur 7.9. Bilete med aktiv snarmaske

Bilete med aktiv snarmaske

Det hender at utvalssverktøya møter grensene sine når oppgåvene blir svært komplekse. I slike tilfelle kan det ofte vere lurt å bruke snarmaske for å redusere problema litt.

3.1. Overview

Normally when you create a selection in GIMP, you see it represented by the "marching ants" that trace along its outline. But really there may be a lot more to a selection than the marching ants show you: in GIMP a selection is actually a full-fledged grayscale channel, covering the image, with pixel values ranging from 0 (unselected) to 255 (fully selected). The marching ants are drawn along a contour of half-selected pixels. Thus, what the marching ants show you as either inside or outside the boundary is really just a slice through a continuum.

The QuickMask is GIMP's way of showing you the full structure of the selection. Activating it also gives you the ability to interact with the selection in new, and substantially more powerful, ways. To activate the QuickMask, click on the small red-outlined button at the lower left of the image window. The button is a toggle, so clicking it again will return you to normal marching-ant mode. You can also activate the QuickMask by selecting in the image window menu SelectToggle QuickMask, or by using the Shift+Q shortcut.

Du kan sjå på snarmaska som eit halvgjennomsiktig lag lagt over biletet. Gjennomsikten til kvart av biletpunkta på maska syner kor synleg kvart punkt skal vere. Dess mindre transparent eit punkt er, dess meir blir det påverka av maska. Fullt markerte pikslar er fullstendig klare. I utgangspunktet er maska raudfarga, men dette kan du endra dersom ein annan farge høver betre.

When you are in QuickMask mode, many image manipulations act on the selection channel rather than the image itself. This includes, in particular, paint tools. Painting with white causes the painted pixels to be selected; painting with black causes them to be unselected. You can use any of the paint tools, as well as the bucket fill and gradient fill tools, in this way. Advanced users of GIMP learn that painting the selection is the easiest and most effective way to delicately manipulate it.

[Tips] Tips

To save the selection done by the Quickmask to a new channel; Make sure that there is a selection and that Quickmask is not active in the image window. Select in the image menu SelectSave to Channel. This will create a new channel in the channel dialog called SelectionMask copy (if you repeat this command you will create a ..copy#1, ...copy#2 and so on...).

[Tips] Tips

Når snarmaska er aktivert, verkar kommandoane klipp og lim bare på utvalet og ikkje på heile biletet. I mange tilfelle kan du gjere deg nytte av dette når du skal overføra eit utval frå eitt bilete til eit anna.

You can learn more on Selection masks in the section dedicated to the channel dialog.