Weird, isn't it? Why are they checkerboardy, and why are they black-and-white when Mastcam is a color camera?

Before I talk about the checkerboard, I just want to note that there's a little block of especially dark pixels -- that's likely a blemish on the detector.

Okay. There are several things going on here. The first has to do with how Mastcam achieves its color vision, which is different from how most space cameras do it. Most space cameras are black-and-white cameras, and you get color pictures by placing three color filters in front of the camera, taking one picture at a time, and combining the three into a single color photo.

Mastcam is more like the camera you might have in your pocket. Its detector has color filters painted on it. But you need three different color filters to reconstruct color as the human eye would see it, so each pixel in Mastcam's detector is painted over with a red, or green, or blue filter, in a design originally described by Bryce Bayer. There are two green pixels for each red and each blue pixel, because the human eye is most responsive to color in that wavelength. The green pixels are arranged just as in a checkerboard; one row goes red, green, red, green, red, green... and the next row goes green, blue, green, blue, green, blue...

(That picture's from Wikipedia.) Now, the pixels sitting behind these filters don't know anything about color; they only know how many photons hit them. So the resulting data file is still technically a grayscale image, but it's one where every fourth pixel shows the number of photons received through a blue filter. The grayscale Mastcam photo at the top of this post is a photo that has not been processed to decode the color information that it contains. It's sort of neat because you can easily see the Bayer pattern. Mars is generally orange, so it's brightest in red wavelengths, darkest in blue wavelengths. It's easy, then, to pick out the blue pixels -- they're the dark ones arranged in a neat pattern.