The DigitalColor Meter utility is built into OS X and provides a powerful color inspector. With it, you can determine the color under the mouse pointer wherever it aims. While this handy tool works in RGB by default, those who love Lab color (or those learning to love it) can easily adjust this tool to display Lab colors instead.
The DigitalColor Meter utility features one big pulldown menu right under its title bar that sets the color space:
With this pulldown set to CIE L*a*b, the real fun begins. Okay, if any of this is actually fun for you, please seek help. While not falling under normal definitions of fun, having a quick way to sample Lab color values of images without having to load them into Photoshop or some other heavyweight application definitely has its benefits. As you mouse over the screen, the Lab channel values are displayed in real time in the utility’s window:
This is useful when learning about Lab as it provides real life colors to examine and the ability to quickly find out their Lab values. I recently used this utility to help judge a photography competition consisting of over 100 entries presented in a web browser. In many of the images, I wanted to know if the image had an unwanted color cast (usually in need of white balancing). The quickest and most reliable way I know to do this is by sampling something neutral (something that should be white or gray) and checking the a and b channel values. A neutral color should have zeros for both a and b. An image with a negative b value of -2 in a neutral area will appear a little cool and blue, with -5 or more giving a strong cold cast. This was just one criterion I used when judging, but I voted down entries that were beautiful but would have been exceptional with a minor warming tweak.
Another thing to consider when using a color picker of any kind (Photoshop, for example) is the sample size. Sampling the color of one pixel may be exactly what you desire, but much of the time (if not all of the time when dealing with a photograph), it’s impossible to pick one color out of the range of colors in a small range around the pointer. When there is a lot of color variation pixel-to-pixel, you can increase the sample size so that an average value of several pixels are taken. In DigitalColor Meter, this is adjusted by moving the Aperture Size slider below the zoomed-in image sample on the right of the window. With this slider all the way to the left, a one pixel value will be measured. As the slider is moved to the right, the sample box will increase in the zoomed-in image to show the sample size. Each increment on the slider increases the sample box by 2 pixels (from 1×1 to 3×3 to 5×5 and so on). Note that you can change the zoom factor of the live display in the application’s preferences and if the zoom is decreased from the default of 8x, the sample size will increase (1×1 at 8x magnification means 2×2 at 4x magnification and so on).
One last tidbit about the DigitalColor Meter utility. When you are moused over an area of interest, you can shift-cmd-C to copy the color values to the clipboard. I have to admit that I do this much more often using RGB As Hex Value mode instead of Lab mode, but either way, it’s nice to know that the capability is there.