bdw000 wrote:Yeah, how believable is it that the ESA can't even tell what color their comet is?
I'm no expert on spacecraft cameras, but I know a little about the imagers used on Earth. Anyone who's done a little
film photography knows about the different films for different lighting conditions. Some of the variations in color temperature have to do with artificial lighting, while others are due to atmospheric effects. Video cameras have electronic compensation known as "white balancing," in which (like film) a white or gray reference is presented.
I remember the first published photos from the Viking landers showed Mars with a pink sky. A later photo including some of the lander's white cowling (with an American flag decal) gave the imaging team the information they needed to color correct the photos. Mars is red, but not
that red.
I know that older probes used black-and-white cameras, yet provided color images by taking a sequence shot through different color filters. This "color separation" is how color photos were once prepared for printing. It is also how older video cameras worked. Today's cameras might use three imagers (CCD, CMOS) built into a prism, or full color may be delivered by a single imager with the colored filters patterned over the face. However the data are gathered,
reproducing the correct color is still a debated issue.
On top of all that, electronic imagers have a natural sensitivity to infrared, which must be filtered. Some photographers will have the IR filter removed from an older camera so that they can use it to experiment with
infrared photography. (Do not confuse IR photography with thermography.)
At a guess, I would say B&W imagers are still preferred for higher resolution, although a three-sensor camera (as opposed to a single sensor) might cover that need. One might also think that there should be enough sensors of other sorts on board a space probe to establish what kinds of light are in the environment, but that still leads us back to the debates over color reproduction.
(Still, processing images to show what a scene would look like
to human eyes may throw away vast amounts of data.)