Selection Tools II

• 01
  Fuzzy Select — Contiguous Colour Regions

  Activate Fuzzy Select (U). Click anywhere on a continuous region of similar colour — a white wall, a clear sky, a solid background. GIMP expands outward from the clicked pixel, selecting all touching pixels within the Threshold tolerance. Unlike Select by Color, Fuzzy Select stops at any pixel outside the tolerance — it cannot jump across gaps. Key Tool Options: Threshold (same as Select by Color — higher selects more broadly). Select Transparent selects transparent pixels if the layer has an alpha channel. Sample Merged samples colour from all visible layers instead of just the active one — useful when working on a flat composite. Shift+click to add new contiguous regions; Ctrl+click to subtract.

  Toolbox → Fuzzy Select (U) → click target region → adjust Threshold in Tool Options
• 02
  Fuzzy Select: Handling Imperfect Backgrounds

  Real backgrounds are rarely a single colour. When Fuzzy Select misses regions, combine it with boolean operations: click the main background area to establish the initial selection, then Shift+click each missed patch to add them. If you overshoot into the subject, Ctrl+click to subtract. For background removal, the most efficient workflow is: select the entire background with multiple Fuzzy Select clicks, then invert (Ctrl+I) to get the subject. This "select what you don't want, then invert" approach is often faster than trying to select a complex subject directly.

  Multiple Shift+clicks to add regions → Ctrl+click to subtract → Ctrl+I to invert for subject
• 03
  Intelligent Scissors — Edge-Snapping Path Selection

  Activate the Scissors (Intelligent Scissors) tool (I). This tool detects contrast edges and snaps the selection boundary to them as you place seed points around the subject. Click to place the first seed point on the subject's edge. Move the cursor along the edge and click to place the next point — GIMP draws a path that snaps to the strongest contrast boundary between your clicks. If the path goes wrong, press Backspace to remove the last seed point and retry. Continue placing seeds around the entire perimeter. To close and convert to a selection: click the first seed point again (a small circle appears near it), then press Enter. The result converts to a standard marching-ants selection.

  Toolbox → Scissors / Intelligent Scissors (I) → click seeds around edge → click first point → Enter to convert
• 04
  Intelligent Scissors: Controlling Edge Sensitivity

  In Tool Options, Edge Detection can be enabled or disabled. With it enabled, GIMP uses the Differential of Gaussian (DoG) algorithm to find edges — useful on photos with clear subject-background contrast. Disable it on low-contrast subjects (GIMP will use straight lines between seed points instead, behaving more like Free Select). Magnetic mode (also in Tool Options) increases the snap strength. Place more seed points in areas where the edge is ambiguous or the background and subject colours are similar — the denser the seeds, the more control you have.

  Tool Options → Edge Detection checkbox → adjust sensitivity with more seed points in complex areas
• 05
  Foreground Select — Subject Isolation with Painting

  Foreground Select is designed for subjects against relatively uniform backgrounds. Activate it from the Toolbox. The workflow has three distinct stages: First, draw a rough lasso around the subject (the entire subject must be inside this rough outline — it doesn't need to be precise). GIMP creates an initial mask, shown as a blue overlay covering the background. Second, paint over the foreground subject with a brush stroke (the paint colour doesn't matter — GIMP is sampling the colours you drag over, not painting them). Paint strokes should cover all the colours present in your subject. Third, press Enter to calculate. GIMP analyses the colour difference between your foreground samples and the background and generates a refined selection. You can refine further by painting more strokes on missed areas.

  Toolbox → Foreground Select → 1) draw rough outline → 2) paint over subject → 3) Enter to calculate
• 06
  Foreground Select: Stroke Size and Refinement

  In Tool Options, the Stroke Width controls how many pixels the sampling stroke covers. Use a larger stroke (50–100px) for the initial rough pass to sample a broad range of foreground colours. Use a smaller stroke (10–20px) for refinement passes targeting missed details. After pressing Enter, the blue overlay updates to reflect the new selection. Areas shown in blue are excluded (background); unmasked areas are included (foreground). Paint additional strokes on any blue areas that should be included — these are missed foreground areas — then press Enter again to recalculate. Repeat until the selection is clean, then click "Select" in Tool Options or press Enter a final time to convert to a standard selection.

  Tool Options → Stroke Width → paint over missed foreground areas → Enter to recalculate → repeat until clean
• 07
  Quick Mask — Painting Selections Directly

  Quick Mask is the most powerful selection refinement tool in GIMP. It converts the current selection into a red overlay that you can paint on directly — painting with white adds to the selection (removes the red mask), painting with black subtracts from it (adds red mask). To enter Quick Mask: press Shift+Q, or click the small dashed square icon in the bottom-left corner of the canvas. The canvas shows your image with a semi-transparent red overlay covering the unselected areas. Use any painting tool — brush, eraser, airbrush — to refine the mask. Zoom in to 200–400% for fine edge work. Press Shift+Q again (or click the icon) to exit Quick Mask and convert the painted mask back to a standard selection.

  Press Shift+Q to enter Quick Mask → paint white (add) / black (subtract) → Shift+Q to exit and convert
• 08
  Quick Mask: The Professional Refinement Pipeline

  The most effective use of Quick Mask is as a final step after any other tool: make a rough selection with Fuzzy Select or Foreground Select, enter Quick Mask, and refine. In Quick Mask, use a hard brush at 100% opacity for sharp edge areas. Use a soft brush at 30–50% opacity to build partial selection transparency for soft edges such as hair, fur, or motion blur. Use the Smudge tool at low strength to blend the mask edge. Zoom in to 300–500% to work individual pixels. When editing the mask, remember: you are painting on a greyscale channel — every painting tool's opacity and dynamics apply, giving you precise sub-pixel control over the selection.

  After rough selection → Shift+Q → hard brush for sharp edges, soft brush for soft edges → zoom in → Shift+Q to exit
• 09
  Adding an Alpha Channel Before Cutting Out

  Before deleting the background from a cutout, the layer must have an alpha channel — otherwise the deleted area fills with the background colour rather than becoming transparent. Check the Layers panel: if the layer is named "Background" (italicised), it has no alpha channel. Add one before any deletion: Image → Flatten Image removes all alpha channels (avoid it until export). Right-clicking the layer in the Layers panel and choosing "Add Alpha Channel" is the correct step. After adding alpha, deleting a selection produces transparent pixels (the checkerboard pattern).

  Right-click layer in Layers panel → Add Alpha Channel → then delete/cut selection
• 10
  Grow + Feather: Cleaning Up Cutout Edges

  After any background removal, zoom in to 200% and inspect the subject's edge. A common artefact is a "fringe" — a 1–2 pixel halo of background colour that remained inside the selection boundary. Fix it with two steps: Select → Shrink by 1–2 pixels (bites into the edge, removing fringe pixels from the selection), then Select → Feather by 0.5–1 pixel (slightly softens the new hard edge). With this refined selection active, delete the selected area of a duplicate background layer to remove fringe, or use Colors → Curves to darken the fringe pixels so they blend with the new background.

  Reload selection → Select → Shrink by 1–2px → Select → Feather by 0.5–1px → clean up fringe

Open a photo with a clearly defined subject against a relatively simple background — a person, object, or animal. You will cut the subject out completely and place it on a white background layer, then inspect and refine the edge.

• A
  Prepare the file

  Open the photo. Duplicate the base layer (Shift+Ctrl+D) and work only on the duplicate. Add an Alpha Channel to the duplicate: right-click the layer in the Layers panel → Add Alpha Channel. Create a new plain white layer below the duplicate (Layer → New Layer, Fill: White) — this will be your "reveal" layer to see the cutout result clearly.

• B
  Make the initial selection with Foreground Select or Fuzzy Select

  Choose whichever tool suits your image. For Foreground Select: draw rough outline → paint over subject → Enter. For Fuzzy Select: click background areas repeatedly with Shift to add regions until the full background is selected, then invert (Ctrl+I). Accept that this initial selection will be imperfect — that's what step C is for.

• C
  Refine with Quick Mask

  Press Shift+Q to enter Quick Mask. You should see a red overlay on the background (or subject, depending on your selection). Zoom in to 200%. Paint white with a hard brush at 100% opacity to include any missed subject areas (removes red). Paint black to exclude any background that leaked into the selection (adds red). Pay special attention to edges. Press Shift+Q to exit.

• D
  Delete the background and inspect the edge

  With the subject selected and the duplicate layer active, press Delete. The background becomes transparent and the white layer beneath is visible. Zoom in to 200–300% and inspect the edge. Apply Select → Shrink (1px) and Select → Feather (0.5px) if a fringe is visible. Zoom out to 100% and evaluate the overall result.

Using the cutout you created in the Guided Practice, place the subject onto a completely different background photograph. No step-by-step guidance — use the tools and techniques from Sessions 2, 3, and 5.

• →
  Open a new background image and paste the cutout subject into it

  Open a second photo as the new background. Copy your cutout layer (Ctrl+A on the cutout layer, then Ctrl+C). Switch to the background photo and paste (Ctrl+V). Promote the floating selection to a new layer. Scale and position the subject appropriately using the Scale and Move tools.

• →
  Match the lighting — apply a colour and tone adjustment to the subject layer only

  Real composites fail because the subject and background have different lighting. On the subject layer (not the background), use Colors → Curves to match the approximate brightness of the background. Then use Colors → Color Balance to nudge the subject's colour temperature toward the background's tone. This session's tools selected the subject — Session 8 will formalise the colour matching technique.