Mercury in natural color
Two MESSENGER global views of Mercury during Jan 14, 2008 flyby. On the left is the inbound view, while on the right the final global view.
Unlike my previous version of the global image that was fudged based on Mercury surface spectra, this one uses calibrated wide-angle camera color data. The old processing should now be rendered obsolete.
The images here were processed to accurately represent color and contrast on computer screens.
The necessity of this processing (essentially just applying a simple 2.2 gamma function) can be seen on the following (b/w) example images of the Moon.
To the left is an ordinary digital camera view of the Moon which follows closely what human eye sees because ordinary digital cameras already take into account specifics of computer (or TV) screens.
The rightmost image is a Cassini wide-angle view of the Moon showing a similar geometry with the original intensity data just converted into a greyscale image.
The middle image is the same Cassini image, but with 2.2 gamma applied.
Notice how the digital camera image contrast and the corrected Cassini image look practically identical (the contrast between lunar maria and highlands), unlike the linear data at right.
It can be seen that without applying gamma to the linear data one gets when calibrating spacecraft images, the resulting image contrast is much higher than in reality. The other Mercury montage showing this same view is just such a linear conversion, it's great for showing contrasts and intensifies color, but is unrealistic.
Credit: NASA / JHUAPL / Gordan Ugarkovic