Why can't NASA use color cameras?

The camera on the Phoenix lander's robotic arm has three color channels: green, red, and near-infrared. If NASA decides to combine data for a particular image from all three channels into a single, false-color image, it will do so; on several occasions, it has done so. Below is a link to such an image.

Although as humans we have a very strong urge to just want to see Mars as the lander does, this is not terribly scientifically valuable. The three channels chosen do not exactly correspond to the red, green, and blue channels of human color vision, because NASA has determined that more compelling data can be collected elsewhere in the EMR spectrum, for example, in the near-infrared region. When you spend many millions of dollars and send it hurtling to another planet, you think these things through to get the most bang for your buck, not the prettiest pictures.

Any digital camera works by taking a series of black and white images through different colour filters. "One-shot" colour cameras have a patterned mask of filters which means that the resolution is only one third that of the total number of CCD or CMOS cells. A black and white image preserves the full resolution of the imaging chips.

The cameras on Phoenix have a number of filters and black and white images taken through them can be combined to give "true-colour" images (some have been composed and released.) However there are filters that show up other wavelengths and combining such "false-colour" images can be important to demonstrate various properties of the soils and rocks around the lander. The point is that the equipment carried is there to achieve a scientific purpose, making pretty pictures for the rest of us to put up on our walls or computer screens is only a secondary concern.

The cameras on the lander, like all serious astronomical research cameras, synthesize colour images by combining images made through different coloured filters. This is necessary to maintain the scientific integrity of the images. Colour cameras are notoriously inaccurate for serious scientific purposes. Virtually _all_ astronomical images you see, whether by the Hubble, the Mars landers, or advanced amateur astronomers, are made from multiple monochrome images shot through carefully calibrated filters. That's the way scientific photography works.

Bandwidth is the simple answer. A colour image takes a lot more time to transmit when they can actually reconstruct the colours using the known characteristics of the CCD and a reference plaque in view (against which they calibrate).

The processing is done on Earth and is called "False Colour". It is a good approximation of the real situation without clogging the channels with information that is not relevant to the *science* of the mission. Remember, that colour might make good tourist snapshots, but things like chromatography, infrared and ultraviolet etc are much more useful to us in understanding that environment.