Click here for a high-resolution JPEG of the image above 

 
Bright areas are relatively warm, and dark areas may be cooler. In the "raw" image on the left, the bright region corresponds to the sub-solar point; there is a brightness gradient roughly symmetrical about the sub-solar point, actually skewed a bit towards mid-afternoon due to thermal inertia. 

The middle image shows a specially processed (unsharp-mask) version of the T-ReCS data that accentuates finer details. The right image is a composite of visible data from the Mars Global Surveyor (National Geographic Society, MOLA Science Team, MSSS, JPL, NASA) taken from the Mars Now webpage and shows Mars at approximately the same orientation during the time of the T-ReCS observations. Comparison of the infrared and visible images shows that many details, such as the southern polar cap and Olympus Mons (upper center large volcano), can also be seen in the T-ReCS processed image. Sun-facing slopes are warmer. The cold patches in the equatorial region, right-hand side must be due to condensate clouds or hazes. 

Dr. Alfred McEwen (Lunar and Planetary Laboratory) suggests that, "the cool region over the south pole is due to CO2 frost, buffered at the CO2 frost temperature near 140K. An east-west trending stripe or arc of slightly cooler surface (equatorial, left-to-middle) corresponds to the brighter (higher albedo) stripe seen in the visible image (right image). A combination of high albedo and perhaps also higher thermal inertia keep this region a bit cooler in the day time. Other spatial variations are due to some combination of albedo, thermal inertia, atmospheric condensates or atmospheric dust." 

More information about T-ReCS can be found at the Gemini website or the instrumentation program-link at www.astro.ufl.edu.