One simple setting in Photoshop can make your life a little easier and your work a little smarter. That may be a bit of a hyperbole, but altering the sample size of the eyedropper tool in Photoshop from the default setting makes sense most if not all of the time. The how and why of this easy configuration setting will be covered in this Tech-Recipe.
The eyedropper tool in Photoshop is used to slurp up a color visible on the screen. The technical term for slurp is sample and the process seems simple: hold the eyedropper icon over a pixel of the image and click to sample that color. While the eyedropper works well in that simple way, noise in the image can cause significant variation from pixel to pixel in an area that should be about the same color. For example, a small 10×10 pixel area in this image on the left is expanded on the right:
The 100 pixels in this square are from an area that should be neutral (the dish was white) and uniform in color. However, the pixels vary in the Lab color space from 35 to 50 in the L channel, 1 to 6 in the a channel, and 0 to 3 in the b. For those not familiar with Lab values, here are the RGB equivalents to show the significance: R(89-125), G(81-110), B(77-112). Even if you zoomed into this level to select one specific pixel to represent the color of this area, which one would you pick?
The problem is that because of this noise, there is no single pixel that accurately reflects the area. Taking an average of several pixels provides a much more accurate guess under most circumstances. To change the sample size of the eye dropper tool, select the tool first (press the letter I) and change the Sample Size setting with the pulldown menu that appears:
While I picked an image with substantial noise (shot at high ISO) to make this demonstration, this setting is important and useful for all digital images regardless of how “clean” they look. I leave my sample size at 3×3 as my default, although for an image this noisy I bump it up to 5×5. I only sample individual points when working with images at very low DPI resolutions where variations over a few pixels are significant.
One of the most useful effects of this setting is not related to picking colors with the eyedropper but when examining colors with the info display (Window -> Info) regardless of the tool selected. In this display, the values of the color in the color space(s) of your choice are displayed as you mouse over an image. The sample size used for this display is affected by the eyedropper sample size, too, so it makes it much easier to estimate the color cast over a noisy image, for example.