The Mask That Behaves Like a Selection
A designer needs a soft vignette and a localized color grade on a landscape photo. They made a selection with the Lasso, then pressed the Add Layer Mask button, expecting a soft edge. The result has a hard, jagged edge. They also duplicated the background and applied a Levels adjustment directly to the duplicate, then tried to reduce its strength with the layer's Opacity slider - the image went flat and gray instead of subtler.
1. Why is the mask edge hard, and how should the vignette mask be built?
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The mask inherits the selection's hard edge - a Lasso selection has no feather. Fix: with the mask selected, use Filter > Blur > Gaussian Blur on the mask itself (masks are editable channels), or rebuild the selection with Select > Modify > Feather or Select and Mask before masking. For a vignette, a better approach is a radial gradient painted into the mask (black to white) or a Gradient fill layer's mask, which gives smooth falloff and is easy to reposition.
2. Why does lowering Opacity make the Levels layer look gray instead of subtler?
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Levels was applied destructively to the pixel layer, so Opacity blends the adjusted pixels with the layer below - but if there is no layer below (or it is the same image), the blend produces a washed, gray result rather than a partial adjustment. The correct tool is a Levels adjustment layer, where Opacity blends the adjustment against the untouched image beneath, producing a genuine partial grade. If stuck with the baked layer, set the blend mode to Luminosity or Normal with a mask, but the adjustment layer is the right fix.
3. How do you confine the color grade to the sky only, and keep it editable?
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Add a Levels or Color Balance adjustment layer, then mask it: select the sky (Color Range or Select Sky), add the mask, and refine with a gradient so the transition to the horizon is smooth. Keep the mask editable - paint black/white to correct, and use Select and Mask on the mask for hairline transitions. Because the adjustment is a layer, you can revisit its strength, color, and mask at any time without touching pixels.