In GIMP, you can capture information about the parts of an image, including the color values used in individual pixels. By establishing the colors used in an image, you can then use the same color values elsewhere in your project, making the colors match up. Use the Color Picker tool in GIMP to detect color values, and then apply those values to any subsequent drawing actions you carry out.
With an image open in GIMP, use the Color Picker tool to record color values you want to match. Select the Color Picker tool by choosing "Tools," and then clicking "Color Picker." Another way to select the tool is via the Toolbox dialog, which you can open by clicking "Windows," and then choosing "Toolbox" from the menu. The Color Picker icon looks like an eye dropper, with "Color Picker Tool: Set colors from image pixels" appearing when you hover your mouse pointer over it. Clicking the tool selects it for use within your image file.
With the Color Picker tool selected, you can detect the color value within any pixel in your image file. To make sure you choose the correct part of the image, you may need to zoom in to the relevant part using the zoom controls at the bottom of the GIMP window. The Color Picker chooses the value from a single pixel, so ensure you choose an appropriate pixel if you plan on using the color elsewhere and need the two areas to match. Click a pixel to have Color Picker detect the color value within it.
With the Toolbox window open, you can display additional information about the currently selected tool using the Tool Options area; display this by choosing "Windows," clicking "Dockable Dialogues," and then selecting "Tool Options." The options appear in the bottom section of the Toolbox window. You can choose to apply a sample average radius value, use sample merged selection or select a Pick Mode, for example. Pick Mode determines what will happen to the detected color value. If you plan on using the color in subsequent drawing actions, select "Set foreground color" from the list. Checking the "Use info window" box displays additional information, including RGB values, when you make a selection using the Color Picker.
Once you have a color value selected using the Color Picker, you can then use the color in your drawing and painting actions. If you selected the option to use the color as foreground, it will be the default color GIMP uses for the next drawing operation you carry out. GIMP will retain the color as foreground color until you change it. To use the color again in the future, you can opt to add it to the palette -- instead of setting it as foreground color -- when you select it using the Color Picker.
Information in this article applies to GIMP 2.8. It may vary slightly or significantly with other versions.
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