Selections
A selection defines the area your edit applies to, so the rest of the image stays untouched. The marching ants show what you have selected. Selections are the foundation for masks, local adjustments and cutouts.
Photoshop has plenty of selection tools: from the rectangular marquee and lasso to quick selection and the magic wand. Make your selection and turn it straight into a layer mask, so you can adjust your edit later. For soft edges use feathering or the Select and Mask workspace. Tip: hold Shift to add to a selection and Alt to subtract from it.
Related terms
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The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.