More GIMP Tricks for Doctoring Images (part 2) - page 2
Many Ways to Make Selections
You have lots of ways to create and modify a selection. But it's hard to tell when it's just right without copying the selection and pasting somewhere else. For real control, you're better off using a Layer Mask.
Start in the Layers dialog (Windows->Dockable dialogs->Layers). Right-click in your active layer -- either over the preview thumbnail or the title -- and choose Add Layer Mask... (Figure 6).
If you're starting from scratch, just click Add in the dialog that pops up -- the default values are usually fine. But if you already have a selection, you can Initialize Layer Mask to: Selection. Or you can initialize to the channel where you saved your selection.
With the layer mask active, anything that isn't in the layer mask disappears (Figure 7).
You can see a thumbnail of what the mask in the Layers dialog. Remove the selection after creating the mask, with Select->None -- you don't need a selection once you have a layer mask.
A layer mask works just like the Quickmask -- paint the mask white in places where you want to see your image, black in places where you don't. But a layer mask is "live" -- you can see what you're doing in the real image while you paint. That's especially helpful when you have other layers underneath the layer you're editing (Figure 8).
As long as the mask has a white border in the Layers dialog, as in Figures 7 and 8, when you paint in the image you'll be painting on the mask. You'll see parts of the butterfly photo appear and disappear, rather than seeing what you're painting directly.
When you're finished modifying the mask, click on the thumbnail of the butterfly in the Layers dialog -- or any other layer's thumbnail. You can go back to editing the layer mask at any time by clicking its thumbnail. Right-click to see more options.
Layer masks may seem daunting at first, compared to selections or erasing. But as you work on ever more complicated GIMP images, you'll be amazed how handy they are. Give them a try!