You paint the area you want changed, and the model only touches what you painted. That painted area is the mask, and four tools make one. The Edit page will not run until something is masked, so this is not an optional refinement, it is the step.
The tools sit in the strip above the canvas, and each has a single letter shortcut.
The four tools
- Brush (B). Paint over the area freehand. The best tool for organic shapes and for topping up a selection another tool got nearly right.
- Magic Wand (W). Click one point and it selects the connected area of similar colour around it. The fastest way to take a whole sky, a wall or a floor. Hold Shift and click again to add another area to the same selection.
- Lasso (L). Click and drag to draw a freeform outline, and it snaps to the edges it finds as you go. Use it on an object that has a clear boundary.
- Eraser (E). Removes mask, rather than removing image. Use it to pull a selection back off something it spilled onto.
The two numbers in the strip
Size, from 1 to 100, sets the brush and the eraser. The [ and ] keys step it down and up without leaving the canvas, which is quicker than reaching for the slider.
Tolerance, from 0 to 100, appears when the wand is active and decides how far the wand travels from the colour you clicked. Low tolerance stops at the first change of shade, which is what you want on a crisp edge. High tolerance carries across gradients, which is what you want on a sky that shifts from pale to deep. If the wand takes far too much, lower it and click again.
Undo, redo and starting over
Ctrl+Z undoes and Ctrl+Shift+Z redoes, both across every tool. The bin icon clears the whole mask and gives you a clean image to start again from.
The ? button opens all of this as a short list on the page, which is worth knowing about because nothing else on the canvas advertises the shortcuts.
How to get a clean result
- Mask a little wider than the object. A mask that stops exactly at an edge often leaves a hairline of the original, which reads as a seam.
- Mask the shadow too. If you are removing or replacing an object, its shadow is part of it. Leaving the shadow behind is the single most common giveaway.
- Work in passes. Wand for the bulk, brush for the corners, eraser to tidy.
Once the mask is right, the words you type decide what fills it, and there are three modes that change what those words mean. See the three Edit modes.