I was working in the lab late last night
When my eyes beheld an eerie sight
For the image from its bits began to rise
And suddenly to my surprise

It was a pan
It was a monster pan
The monster pan
It was a Martian smash
I did the pan
It caught on in a flash
I did the pan
I did the monster pan.
(Apologies to Bobby "Boris" Pickett)

13 frames covering 180 degrees...39 raw images...half a gigabyte of hard disk space...special software...about 20 hours with my nose two inches from the monitor...well, here it is, the too-aptly-named "Monster Pan". Dr. Frankenstein would love it.

(You know what to do with the mouse)

The pan presented some interesting technical challenges [ominous muttering from the audience] that required writing some custom software [groans]. Now, I know that I can knock people unconscious halfway around the world by uttering the famous phrase "And now for the GeekSpeak" [thumps, thuds, crash of overturning chairs] oops, sorry, I'll try to be more careful. To make a long story short [pause for applause], the brightness of the raw images varied wildly from frame-to-frame, and between channels within each frame (which means that the resulting colors would vary wildly). The software [gnashing of teeth like the sound of crickets]...seriously, there's a reason I have to explain a little, and I'll try to keep it brief [applause]...anyway, the software worked by starting from a reference frame (#8, containing the small crater on the floor of Bonneville) that was in pretty good shape, and one-by-one left and right adjusting the brightness of the raw images to match the preceding image in the chain.

["Get to the point!"] OK, OK. The point is this: With brightness controlled, you'll see that both the average hue as well as the saturation ("vividness of color" for you civilians) varies smoothly around 180 degrees. I think that is a genuine effect, and that it tells us something about the perrenial question of The True Color of Mars. It's due to the angle between your eyes (well, Spirit's "eyes"), the objects in the scene, and the Sun, all of which changes the properties of the colors. With the Sun behind you the colors are vivid; looking into the Sun, with objects shadowed, the colors are muted; and everything in-between.

In other words, the answer to the question "what color is Mars, anyway?" is: "It depends on which way you're facing".

The saturation is generally too high in the image, but when I tried to crank it down to make the extreme ends look more natural, the center faded away to grey. I take this as a sign that, to some degree anyway, there really is a lot of saturation in the colors.

And then there's the sky. I have to admit that it's sort of a fake, and actually looks like this:

This is interesting [snorts, coughs], because I think that it was the bright sky that swamped the exposure sensors and led to the brightness problems. The sky was consistent in the raw images; controlling the brightness of the ground made the sky go whacko. The way I created the sky in the finished version isn't entirely invalid: I picked two points in the sky of the uncut image, at the ends, and one in the center (at the reference frame), where the colors were relatively normal, measured the colors at those points, and created a double gradient to fill the sky.

["Yeah, so?"] So, the sky is quasi-real, and illuminates (forgive the pun) the related question "What color is the sky on Mars?" The answer (bet you can see it coming): "It depends on which way you're facing". Note that the color of the sky is sort of consistent with the color of the ground beneath it.

So there you go. I need to get some sleep.