3. The Quick Mask

Figura 7.9. Image with Quick Mask enabled

Image with Quick Mask enabled

The usual selection tools involve tracing an outline around an area of interest, which does not work well for some complex selections. The Quick Mask, however, allows you to paint a selection instead of just tracing its outline.

3.1. Panoramica

Normalmente, una selezione in GIMP, è visibile grazie al tratteggio tipo «formiche che camminano» delineato intorno alla zona, anche se, questa è molto più di ciò che appare. Infatti in GIMP una selezione è in realtà un canale in scala di grigi che ricopre l'immagine, con i valori dei punti che vanno da 0 (non selezionato) a 255 (selezionato completamente); il tratteggio viene disegnato sul bordo dei punti che sono selezionati esattamente per metà. Perciò il tratteggio, separando una zona interna da una esterna, è realmente solo un limite posto sopra una zona continua.

The Quick Mask is GIMP's way of showing the full structure of the selection. Quick Mask also provides the ability to interact with the selection in new, and substantially more powerful, ways. Click the small outlined button at the lower left of the image window to toggle Quick Mask on and off. The button switches between Quick Mask mode, and marching ants mode. You can also use SelectToggle Quick Mask, or Shift+Q, to toggle between Quick Mask and marching ants mode.

In Quick Mask mode, the selection is shown as a translucent screen overlying the image, whose transparency at each pixel indicates the degree to which that pixel is selected. By default the mask is shown in red, but you can change this if another mask color is more convenient. The less a pixel is selected, the more it is obscured by the mask. Fully selected pixels are shown completely clear.

In Quick Mask mode, many image manipulations act on the selection channel rather than the image itself. This includes, in particular, paint tools. Painting with white selects pixels, and painting with black unselects pixels. 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 the image.

[Suggerimento] Suggerimento

To save a Quick Mask selection to a new channel; Make sure that there is a selection and that Quick Mask mode is not active in the image window. Use SelectSave to Channel. to create a new channel in the channel dialog called «SelectionMask copy» (repeating this command creates «…copy#1», «…copy#2» and so on).

[Suggerimento] Suggerimento

In Quick Mask mode, Cut and Paste act on the selection rather than the image. You can sometimes make use of this as the most convenient way of transferring a selection from one image to another.

È possibile approfondire l'argomento delle maschere di selezione nella sezione dedicata alla finestra di dialogo dei canali.