Why does GIMP report different product colors with Sample merged enabled?

What Changes

The Color Picker selects a color from the image displayed on screen. With Sample merged disabled, the value comes from the active layer. This can differ from the color you see in the finished-looking image if other visible layers add, cover, or alter the product area.

With Sample merged enabled, GIMP samples the visible composite from all visible layers. Hidden layers are excluded. Therefore, the same screen location can produce one value from the active layer and another from the visible composite without either control necessarily malfunctioning.

This is a sampling-scope difference, not proof that one value is the objective material color. Displayed pixels may represent an edited image, and a single pixel may not describe the product surface consistently.

Illustrative Exercise

Illustrative exercise: create two working copies of a fictional product image. In Copy A, the active product layer contains a muted blue patch, while a visible highlight layer lightens that same location. In Copy B, the highlight layer is hidden, but the active product layer is unchanged. These are fictional inputs for learning the control behavior, not completed software test results.

First sample the same location with Sample merged disabled. Record the active-layer result for each copy. Then enable Sample merged and sample that location again. Record the visible-composite result. The expected diagnostic observation is that Copy A can change when the highlight is visible, while Copy B can match the active-layer result because the highlight is hidden.

If the two scope readings are different, continue by identifying which visible layer contributes to the composite. If they are the same, stop treating sampling scope as the explanation and investigate a different cause, such as sampling a different location or using a different image copy. Pass the exercise only when you can state which control produced each recorded value and why the visible layer state matters.

1. 1. Preserve the approved original and work on a test copy.
2. 2. Select the Color Picker and sample one clearly identifiable product area.
3. 3. Record the value with Sample merged disabled; label it active-layer sampling.
4. 4. Enable Sample merged and sample the identical location again; label it visible-composite sampling.
5. 5. Compare the layer visibility and the two results before deciding which reading answers your question.

Use The Right Scope

Use active-layer sampling when you need to inspect the color stored on the selected layer itself. This is appropriate when checking a paint layer, retouching layer, or other isolated source and you intentionally do not want visible layers included.

Use Sample merged when your question concerns the color currently represented by all visible layers at that location. Remember that hidden layers are excluded, so changing visibility changes what the composite sampler can measure.

The Color Picker's Pick Target determines what happens after sampling. Pick only displays the selected pixel's color without otherwise using it. Set foreground color assigns it to the toolbox foreground color, and Set background color assigns it to the toolbox background color. These actions affect how you use the picked result; they do not change whether the sample came from the active layer or the visible composite.

If Add to palette is enabled, the picked color is sent to the active color palette. Treat that saved color as a record of the selected sampling scope and image state, not as an independent physical measurement.

Reduce Local Variation

A single pixel can be unrepresentative near a highlight, edge, texture, or small retouch. Sample average uses a radius slider to calculate an average color from a square sampling area. This can make a reading more useful for a broader product patch, but it also includes every pixel inside that square, including unwanted background or edge pixels.

Editorial diagnosis: use the smallest square area that remains representative of the product surface. If enlarging the radius brings an edge or highlight into the square, stop enlarging it and choose a cleaner location. Record the radius and location alongside the result so a later comparison does not silently change the sampling conditions.

Record Before Acting

Clicking an image opens the Color Picker Information window unless the relevant option changes that behavior. Use info window controls whether the information window opens automatically, and Shift provides a temporary toggle. While using a paint tool, holding Ctrl permits color picking without switching tools; the color-picker dialog is not opened during that operation, and the paint tool remains active after Ctrl is released.

For a product-proof decision, record the image copy, active layer, visible layers, Sample merged state, sample-average state and radius, location, and Pick Target. If the active-layer and composite values disagree, choose the scope that matches the question rather than replacing pixels automatically. Stop and review the image when neither scope represents the intended product surface.

Use this question’s review worksheet

The sample rows are fictional exercise data. Preserve the example, save a working copy and record your own inputs, observations and decisions. The example is not a test receipt.

Fictional manual sampling worksheet (CSV)