Monitor Color Values with GIMP Sample Points Dialog

The Sample Points dialog in GIMP allows you to place persistent markers on specific pixels to monitor their color data continuously while making image adjustments. Unlike standard color pickers that only provide instantaneous readings, sample points remain visible on the canvas and dynamically update their values in real-time as you apply filters, adjust curves, or paint. This guide explains how to open the dialog, place sample points, customize readout modes, and use them to maintain color accuracy throughout your editing workflow.

Opening the Sample Points Dialog

To view your active color targets, you must open the dedicated dialog window:

  1. Go to the top menu and select Windows.
  2. Hover over Dockable Dialogs.
  3. Click on Sample Points.

The Sample Points panel will appear. You can dock this tab alongside your Layers or Channels panel for easy reference.

Adding Sample Points to Your Image

Sample points are generated using the canvas rulers:

  1. Ensure rulers are visible by checking View > Show Rulers (or pressing Ctrl + Shift + R).
  2. Hold down the Ctrl key (or Cmd on macOS).
  3. Click inside either the horizontal or vertical ruler and drag your cursor onto the canvas.
  4. Release the mouse button over the specific area you want to monitor.

A numbered crosshair will appear on the image, and a corresponding numbered entry will display inside the Sample Points dialog. You can add up to four distinct sample points simultaneously.

Configuring Readout Formats and Sample Radius

The Sample Points dialog lets you customize how color data is displayed for each point:

  • Color Model: Click the dropdown menu next to any sample point in the dialog to switch between color representations, such as Pixel, RGB (0–255), RGB (percent), HSV, and Hexadecimal code.
  • Sample Average: By default, a sample point reads a single pixel (1x1). To get a broader, less noisy reading, select the Color Picker Tool (O), check Sample merged or adjust the Sample average radius in the Tool Options dock. The sample point will adopt this average area.

Monitoring Values Across Edits

Once your points are placed, any adjustments applied to the image will reflect immediately inside the Sample Points dialog:

  • Adjustment Tools: When using Curves, Levels, or Color Balance, watch the dialog values shift dynamically as you tweak sliders to ensure highlights don't clip or skin tones remain within target color ranges.
  • Layer Edits: As you add adjustment layers, blend modes, or brush strokes above the sampled area, the readout shows the final composite color value at that location.

Moving and Removing Sample Points

  • Repositioning: Hold Ctrl and click-and-drag an existing sample point crosshair to a new location on the canvas.
  • Deleting: Hold Ctrl, click the sample point crosshair, and drag it entirely off the canvas back into the horizontal or vertical ruler.