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description: "Photoshop Compositing & Retouching — Where Module 2 covered Photoshop's basic mechanics, this module covers the techniques that make Photoshop work feel…"---

06 · Photoshop Compositing & Retouching

Where Module 2 covered Photoshop's basic mechanics, this module covers the techniques that make Photoshop work feel professional: layer masks for non-destructive hiding/revealing, adjustment layers for editable color correction, and the Healing Brush/Clone Stamp for removing blemishes or unwanted objects from a photo.

1. Layer masks

A layer mask hides parts of a layer without deleting any pixels — painting black on the mask hides, white reveals, and gray partially hides. This is the non-destructive alternative to erasing or deleting pixels outright, and it's reversible at any point later.

  1. Select a layer, then click the Add Layer Mask icon at the bottom of the Layers panel (a rectangle with a circle) — a white mask thumbnail appears next to the layer, meaning nothing is hidden yet.
  2. Press B for the Brush tool. Press D to reset colors to default (black/white), then X to swap which one is currently active.
  3. With the mask thumbnail selected (click it once to make sure it's targeted, not the layer image itself) and black as your foreground color, paint over the canvas — the painted area becomes transparent, revealing whatever is on the layer below.
  4. Press X to swap to white and paint back over any area you hid by mistake — masks are fully reversible as long as you keep painting on the mask rather than the pixels.
  5. A common use: place a background photo above a solid-color layer, add a mask to the photo layer, and paint black around a subject to reveal the solid color behind them — a simple manual cutout, without ever deleting a pixel from the original photo.

Selection-to-mask shortcut

If you already have an active selection (Module 2), clicking Add Layer Mask converts that selection directly into a mask — everything outside the selection is hidden immediately, instead of hand-painting.

2. Adjustment layers

An adjustment layer applies a color/tone edit (brightness, hue, levels, curves, and more) to everything beneath it in the stack, without altering any pixels directly — like a mask, it's fully editable and reversible at any time.

  1. Click the half-filled circle icon at the bottom of the Layers panel (or Layer > New Adjustment Layer) and choose a type — Brightness/ Contrast, Hue/Saturation, and Curves cover most everyday needs.
  2. The adjustment appears as its own layer with a mask already attached. Double-click its thumbnail at any time to reopen its settings in the Properties panel and tweak the values further.
  3. Because it has a mask automatically, you can paint black on that mask (same technique as above) to exclude specific areas from the adjustment — e.g. brightening a subject's face without affecting the background.
  4. Adjustment layers only affect layers below them in the stack — drag one up or down in the panel to change what it applies to.
  5. To constrain an adjustment to just the single layer directly beneath it (instead of everything below), click the clip to layer icon between the adjustment layer and the one below it in the Layers panel (or Layer > Create Clipping Mask, ⌥/Alt+⌘/Ctrl+G).

3. Healing Brush and Clone Stamp

Both tools sample pixels from one part of an image and paint them elsewhere, but they behave differently — knowing when to use which one matters.

  1. Clone Stamp (S) — Option/Alt-click a source point, then paint elsewhere to stamp an exact copy of the sampled area, pixel for pixel. Good for duplicating a distinct object or pattern.
  2. Spot Healing Brush (J, then Shift+J to cycle to plain Healing Brush if needed) — just paint directly over a blemish with no separate sampling step; Photoshop automatically samples nearby texture and blends the edges, lighting, and texture to match the surrounding area. This is the faster, more automatic tool for small blemishes (a spot, a scratch, a stray hair).
  3. Healing Brush (Shift+J to cycle from Spot Healing Brush) — like Clone Stamp, requires an Option/Alt-click to set a source point first, but then blends the sampled texture into the destination's lighting and tone rather than pasting it exactly — better than Clone Stamp when source and destination lighting differ slightly.
  4. Work on a duplicated layer (⌘/Ctrl+J) rather than the original so retouching stays non-destructive and reversible by simply toggling or deleting that layer.

4. A basic retouching workflow, end to end

  1. Open a photo and duplicate its layer (⌘/Ctrl+J) — always retouch on the copy.
  2. Use the Spot Healing Brush to remove small blemishes or distracting specks first — it's fast and usually needs no further adjustment.
  3. Use the Healing Brush or Clone Stamp for larger unwanted objects or areas, sampling from nearby similar texture (e.g. clear skin, plain background) so the blend looks natural.
  4. Add a Curves or Hue/Saturation adjustment layer above the retouched layer to correct overall color/tone — mask out any area (like the eyes, if you brightened the whole face) where the adjustment shouldn't apply.
  5. Add a layer mask to the retouched layer itself if you want to blend it back with an untouched version underneath at partial strength, for a more natural, less "overworked" result.
  6. Flatten only your final export copy (Image > Flatten Image, or just export via Export As, Module 2) — never flatten your working .psd, so every mask and adjustment stays editable if you need to revisit it.

Cheat sheet

Tool/Action Shortcut
Add layer mask Layers panel > Add Layer Mask icon
Brush tool B
Reset colors to black/white D
Swap foreground/background color X
Add adjustment layer Layers panel > half-filled circle icon
Clip adjustment to layer below ⌥/Alt+⌘/Ctrl+G
Duplicate layer ⌘/Ctrl+J
Clone Stamp tool S
Spot Healing Brush J
Cycle to Healing Brush Shift+J
Flatten image (final export copy only) Image > Flatten Image

How It Actually Works

  • A layer mask is a grayscale channel, not a special hide/show flag. Internally it's an 8-bit grayscale image the exact dimensions of its layer, stored as a per-pixel alpha multiplier: white pixels (255) pass the layer's own pixel at full opacity, black (0) multiplies it to fully transparent, and any gray value in between scales it proportionally. This is why gray gives partial transparency rather than a binary state, and why masks can be blurred, have levels/curves applied to them, or even copied between layers like any other grayscale image.
  • Adjustment layers store parameters, and get re-evaluated live during compositing, not baked into pixels. A Curves adjustment layer holds a lookup table mapping input tone values to output tone values; when Photoshop composites the stack, it evaluates that lookup against whatever pixel data currently sits beneath it in the stack, every time it needs to render. That's the mechanism behind reopening it later and getting the exact same editable curve back, and also why moving an adjustment layer to a different position in the stack changes its output — it's now being evaluated against different underlying pixels.
  • Clipping masks work by testing layer indices, not visual bounds. When you clip a layer to the one below it, Photoshop flags that layer as "clipped to" the base layer directly beneath it in the stack order; during compositing, the clipped layer's own alpha is multiplied by the base layer's alpha before drawing — so if the base layer's shape changes (a layer mask edit, a transform), the clipped adjustment or content automatically follows without needing to be re-masked by hand.
  • Content-Aware healing tools do texture synthesis, not simple copy- paste. The Spot Healing Brush's Content-Aware option analyzes a ring of source pixels around your brush stroke, looks for patches elsewhere in the image (or synthesizes new texture) that statistically match the surrounding structure and color, and blends the seams using a Poisson- blending-style gradient match so the lighting transition is smooth — this is why it can "invent" plausible texture with no explicit source point, unlike the Clone Stamp, which does a literal 1:1 pixel copy from wherever you Option/Alt-clicked, with no automatic blending of tone or lighting.
  • A .psd's layers, masks, and adjustment parameters are all preserved as distinct data structures inside the file — which is exactly what "flattening" destroys: flattening composites every visible layer down through its masks and adjustments into one single pixel grid, discarding the separate layer/mask/adjustment records permanently. That's the whole reason the workflow above insists on keeping your working .psd unflattened and only flattening a copy at export — there is no operation that reconstructs the original layers, masks, or adjustment values from a flattened result.

Exercise

Open any photo (a selfie, a product photo, or a downloaded stock image). Duplicate the layer and use the Spot Healing Brush to remove at least one blemish or distraction. Add a Curves adjustment layer to improve overall contrast, masking it so it only affects part of the image. Finally, add a layer mask to the retouched layer and paint at 50% gray to partially blend the retouch back with the original underneath it. Export the result as a JPG.