Eyedropper
The Eyedropper tool  chooses a color from an image. A color that is selected by a mouse-click, becomes the main color on the Color palette. If you continue to draw with the Eyedropper pressed you can see a dynamic change in color. Moving the Eyedropper while keeping Shift pressed evenly selects color along all pixels in the cursor's path.
To adjust the tool's parameters go to the Settings Panel. To change the value of a parameter, enter a numerical value in the parameter's field and press Enter (Macintosh: Return) or adjust the slider. To open the Sample Size menu right-click on the image with the mouse.
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Sample Size (1-21). The number of pixels around the eyedropper's tip that are used to average the selected color. At minimum values, the area around the eyedropper's tip is reduced to one pixel. A higher value of the parameter can be used on photos with a lot of color noise (random red and blue pixels on homogeneous background).
Sample Size menu
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— Eyedropper