How to Create CRT Scanlines in GIMP Using Patterns

This guide provides a straightforward method for simulating a retro CRT television scanline effect on your images using custom patterns in GIMP. By creating a simple repeating horizontal line pattern and applying it as an overlay layer, you can achieve an authentic vintage monitor aesthetic with complete control over intensity, blending, and scale.

Step 1: Create the Scanline Pattern

  1. Open GIMP and create a new project by navigating to File > New.
  2. Set the Width to 1 pixel and the Height to 2 pixels (or 2 x 4 pixels for thicker lines on high-resolution images). Under Advanced Options, set Fill with to Transparency, then click OK.
  3. Zoom in fully (around 800% to 1600%) so the tiny canvas is visible.
  4. Select the Pencil Tool with a 1-pixel size and set the foreground color to Black.
  5. Draw a black pixel on the top half of the canvas, leaving the bottom half transparent.
  6. Press Ctrl + A (or Cmd + A on macOS) to select the entire canvas, then press Ctrl + C (or Cmd + C) to copy it to your clipboard. GIMP will automatically make this copied pattern available in your Pattern palette as the "Clipboard Image."

Step 2: Apply the Pattern to Your Image

  1. Open the image you want to apply the scanline effect to via File > Open.
  2. Create a new transparent layer by clicking Layer > New Layer or clicking the New Layer icon in the Layers panel. Name this layer "Scanlines".
  3. Select the Bucket Fill Tool (Shift + B).
  4. In the Tool Options panel on the left:
    • Set the Fill Type to Pattern Fill.
    • Click the pattern preview box and select the first pattern, which is the Clipboard Image you copied in Step 1.
    • Set Affected Area to Fill whole selection.
  5. Click anywhere on the "Scanlines" layer to fill the entire canvas with horizontal stripes.

Step 3: Blend and Fine-Tune the Effect

  1. Ensure the "Scanlines" layer is selected in the Layers panel.
  2. Change the Layer Mode from "Normal" to Overlay, Multiply, or Soft Light, depending on the brightness and contrast of your image:
    • Multiply darkens the lines for a classic low-brightness CRT look.
    • Overlay creates high-contrast, stylized scanlines.
  3. Lower the Opacity of the "Scanlines" layer (typically between 20% and 50%) until the effect looks natural rather than overwhelming.

Step 4: Optional CRT Finishing Touches

  • Slight Softness: Duplicate the base image layer, apply a small blur via Filters > Blur > Gaussian Blur (set to 0.5 or 1.0 px), and place it beneath the scanlines to simulate phosphor glow.
  • Screen Curvature: Merge your layers or select the final composite and go to Filters > Distorts > Lens Distortion. Increase the Main slider slightly to add a subtle CRT screen curve around the edges.