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description: "Photoshop Basics — Photoshop is a pixel-based (raster) image editor: every image is a grid of colored pixels, which makes it the right tool for photos and…"---

02 · Photoshop Basics

Photoshop is a pixel-based (raster) image editor: every image is a grid of colored pixels, which makes it the right tool for photos and painted or composited artwork, as opposed to the scalable vector shapes you'll meet in Illustrator (Module 3). This module covers the workspace, the Layers panel, making selections, cropping/resizing, and exporting — the moves you'll use in nearly every later Photoshop lesson.

1. Workspace tour

  1. Open Photoshop and create a new document: File > New (⌘/Ctrl+N). Pick the Web or Photo preset category, choose any size (e.g. 1000×1000 px), and click Create.
  2. The workspace has four areas you'll use constantly:
  3. Toolbar (far left) — selection, painting, and shape tools.
  4. Options bar (top, under the menu) — changes based on which tool is active; this is where you set brush size, selection mode, etc.
  5. Canvas (center) — your document.
  6. Panels (right, docked) — Layers, Properties, Adjustments, and more.
  7. If a panel is missing, every panel lives under the Window menu — e.g. Window > Layers toggles the Layers panel back on if you accidentally closed it.
  8. Zoom with ⌘/Ctrl + / ⌘/Ctrl -, or ⌘/Ctrl+0 to fit the whole canvas in the window. Hold Space and drag to pan around when zoomed in.

2. The Layers panel

Photoshop documents are stacked layers — think of each as a separate sheet of acetate, composited top-to-bottom. Almost everything non-trivial you do in Photoshop involves managing layers deliberately rather than flattening everything into one.

  1. Open Window > Layers if it isn't already visible.
  2. Click the New Layer icon (bottom of the panel, or Layer > New > Layer, Shift+⌘/Ctrl+N) to add a blank layer above the current one.
  3. Layers higher in the stack draw on top of layers below them. Drag a layer up or down in the panel to reorder it.
  4. Each layer has a visibility toggle (the eye icon) — click it to hide/show that layer without deleting it, useful for comparing versions.
  5. Double-click a layer's name to rename it — do this constantly; "Layer 14" six layers deep is how projects become unmanageable.
  6. Group related layers with Layer > Group Layers (⌘/Ctrl+G) after selecting them (⌘/Ctrl-click or Shift-click to multi-select in the panel) — groups act like folders and keep a complex file navigable.

Opacity vs. Fill

The Opacity slider (top of the Layers panel) fades the whole layer, including any layer styles (like a drop shadow) applied to it. Fill fades only the layer's own pixels, leaving layer styles at full strength — useful for a stroke-only or shadow-only effect on an otherwise invisible shape.

3. Basic selections

A selection tells Photoshop "only apply the next action inside this area."

  1. Marquee tools (rectangle/ellipse) — press M, then drag on the canvas. Hold Shift while dragging to constrain to a square/circle.
  2. Lasso tool — press L, then drag freehand around an area. Use the Polygonal Lasso (cycle with Shift+L) for straight-edged freehand selections, clicking a point at each corner.
  3. Quick Selection tool — press W, then paint over the area you want; Photoshop expands the selection to nearby similar pixels automatically, which is much faster than lassoing a complex shape.
  4. Combine selections without restarting: hold Shift while selecting to add to the current selection, hold Option/Alt to subtract from it.
  5. Select > Deselect (⌘/Ctrl+D) clears the active selection — a command you'll use after almost every selection-based edit.

4. Cropping and resizing

Cropping changes the canvas boundary; resizing changes the pixel dimensions of the whole image. They're different operations and it matters which one you reach for.

  1. Crop tool — press C, drag handles on the canvas edges to define the new boundary, then press Enter/Return to commit (or Esc to cancel). The Options bar lets you type an exact aspect ratio (e.g. 16:9) so the crop stays proportional.
  2. Resize the whole image — Image > Image Size (⌥/Alt+⌘/Ctrl+I). With the link icon next to Width/Height enabled, changing one dimension scales the other proportionally, avoiding a stretched result.
  3. Resize the canvas without scaling pixels — Image > Canvas Size (⌥/Alt+⌘/Ctrl+C) adds or removes blank space around the existing image; use the anchor grid to control which side the new space is added to.
  4. Resizing up (enlarging) a raster image beyond its original pixel count always loses sharpness — Photoshop's "Preserve Details" resampling method in Image Size handles this better than the default, but there's no way to invent detail that was never captured. This is a fundamental difference from Illustrator's vector shapes, which scale infinitely without quality loss (see Module 3).

5. Saving and exporting formats

Photoshop distinguishes between its native working format and export formats meant for sharing or use elsewhere.

  1. File > Save (⌘/Ctrl+S) saves as .psd — Photoshop's native format, which preserves layers, layer styles, and editability. Always keep a .psd as your source file.
  2. File > Export > Export As (⌥/Alt+⌘/Ctrl+Shift+W) gives a live preview dialog for exporting a flattened copy:
  3. PNG — supports transparency, lossless; best for graphics, UI assets, and anything needing a transparent background.
  4. JPG — no transparency, lossy (adjustable quality slider); best for photos where file size matters more than pixel-perfect fidelity.
  5. File > Save a Copy (⌥/Alt+⌘/Ctrl+S) saves a flattened or format- converted copy without altering your open .psd.
  6. For a quick single-format export without the preview dialog, use File > Export > Quick Export as PNG.

Cheat sheet

Tool/Action Shortcut
New document ⌘/Ctrl+N
New layer Shift+⌘/Ctrl+N
Group selected layers ⌘/Ctrl+G
Marquee (rectangle/ellipse) select M
Lasso select L
Quick Selection tool W
Deselect ⌘/Ctrl+D
Crop tool C
Image Size ⌥/Alt+⌘/Ctrl+I
Canvas Size ⌥/Alt+⌘/Ctrl+C
Save (native .psd) ⌘/Ctrl+S
Export As (PNG/JPG with preview) ⌥/Alt+⌘/Ctrl+Shift+W
Fit image to window ⌘/Ctrl+0

How It Actually Works

  • A Photoshop document is a stack of pixel grids composited top-down, and "layer order" is a literal rendering order, not just an organizational convenience. Every raster layer stores its own full grid of RGB(A) pixel values at the document's dimensions; to display or export the image, Photoshop walks the layer stack from the bottom up, blending each layer's pixels over the accumulated result beneath it according to that layer's opacity and blend mode. This is exactly why dragging a layer above or below another changes what's visible — you're changing which pixel data gets composited over which, in a real per-pixel calculation each time the canvas redraws.
  • A selection is a temporary mask stored as a per-pixel boundary/region, which every subsequent tool checks before it's allowed to affect a pixel. Internally, an active selection is tracked much like the grayscale mask channel described in Level 1's compositing module (full selection = fully affected, partial/feathered selection = partially affected), scoped to the whole document rather than one layer. That's why "Deselect" matters: leaving an old selection active silently constrains every later edit to that stale region, since tools have no way to know a selection is "supposed to" be cleared — they simply always check whatever selection state currently exists.
  • Canvas Size and Image Size manipulate two different data structures entirely: Canvas Size changes the document's pixel-grid boundary without touching any layer's stored pixel data, while Image Size actually resamples — recalculates — every layer's pixel grid to a new total pixel count. Resampling requires an interpolation algorithm (Photoshop's resample methods, including "Preserve Details") to invent intermediate pixel values when scaling up, since there is no way to derive detail that the original capture never recorded — which is precisely why enlarging a raster image loses sharpness in a way a vector shape (Module 3) never does: vector paths re-evaluate exact math at any size, raster pixels can only ever be estimated at a size larger than they were captured.
  • PSD preserves every layer, mask, and style as separate stored objects; PNG and JPG store one single flattened pixel grid, which is the entire mechanical reason "Save" and "Export" are different operations with different purposes. Exporting composites every visible layer down through the same top-down blending process described above into one final grid before writing it to the export format — a real, one-time computation whose result is then the only thing the exported file contains, with no separate layer data preserved to edit further.

Exercise

Create a new 1200×800 px document. Add three layers: a solid-color background, a shape or pasted image on top, and a text layer. Rename all three layers descriptively and group the shape and text layers together. Use the Quick Selection tool to select just the background layer's content and fill it with a different color. Crop the canvas to a 1:1 square, then export a flattened PNG and a JPG at 80% quality, and compare the two file sizes.