Mercury mosaics from January 2008 Flyby Options

[volcanopele]

The raw data from MESSENGER's January 14, 2008 flyby of the planet Mercury are now online on NASA Planetary Data Service's website:

http://pds-imaging.jpl.nasa.gov/data/messe...grmds_1001_new/

As such, I am proud to present a series of mosaics I have created using these raw images. These use the mosaic designs shown on the MESSENGER project's Mercury Flyby 1 Visualization Tool webpage. These mosaics were created in either Photoshop CS3 (using the Photomerge tool) or PTGui Pro (particularly for the two MASSIVE mosaics).

Keep in mind that these mosaics are quite large in most cases, and it may be better just to right-click and save them to your hard drive to view them separately, rather than viewing them in your browser.

[ilbasso]

Wow, that's almost as big as the planet itself! Incredible detail. You can even see the rim in profile of a crater on the limb at 4:00. The detail at the terminator is mesmerizing.

[tedstryk]

I LOVE this version! Not to mention the fact that for Mercury, the dynamic range issues that crop up with gamma correction are huge, given the intense solar illumination.

[ugordan]

Thanks, all. It'd be even better if it was properly geometrically reprojected. Oh well...

Ted, gamma correction has nothing to do with the amount of illumination - you simply darken the image/change the exposure. It has to do with the amount of contrast and how the physical brightness is mapped to the nonlinear video device. A corect gamma actually ensures proper DN - brightness mapping, it's not black magic of some kind. The problem is the sRGB colorspace nowadays assumes 2.2 gamma function, which digital cameras, video cameras etc. will automatically output. Spacecraft data, when calibrated, is linear so a difference arises if you simply shove the calibrated intensities into RGB values.

I'm sure you're perfectly aware of this, but for others - take a look at the following image (click):


The image on the left is a digital camera image of the Moon, which approximates what human eye sees. The image on the right is a calibrated Cassini WAC image, no gamma correction - the same as Mercury here. The middle image is the Cassini image with 2.2 gamma. Note gamma doesn't overexpose the data, I brightened the middle image to match the left one better. Both the left and middle images nicely show the Moon as it appears, while the image on the right does not.

The advantage you're probably thinking here of no gamma correction is that Mercury has lower albedo variations than the Moon does, so it would wash out details. Then again, that's how the planet actually looks like. Something like this, for better or worse.

[tedstryk]

I understand the concept. The problem is that the range from the darkest black to the brightest white is huge, especially when compared to places such as the Saturnian system. A computer monitor can't come anywhere close to portraying such a range. In fact, it is only at the Uranian system that one could truly show the full range on a monitor. The problem is that even on the best monitor, the darkest dark is nowhere near true black, and the brightest white is relatively dark compared to daylight outdoors. As a result, A lot of the detail that the eye could discern were it viewing the real planet is lost. I find the whole issue to be a lot like trying to make a flat map of a round world. No method is truly "accurate" - each have their advantages and disadvantages.

The problem in that example is that in both gamma-corrected images, the whites are murdered, especially in the Cassini one. Looking through a telescope, that wouldn't happen.