Credit: NASA/JPL/Arizona State University
(This post and the next one or two will highlight the capabilities of THEMIS.)
The THEMIS VIS (visible light) camera on board the 2001 Mars Odyssey is capable of capturing color images of the Martian surface using five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from using multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.
The above false color image shows one portion of the surface in the Meridiani Planum region (1.6° North, 5.6° East). The overall image covers an area of 18.4 km by 65.7 km, at a resolution of 36 meters per pixel. The Opportunity rover landed west of this image. This image was collected during the northern spring season, and was released to the public on May 23, 2005.