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Posted by: djellison Mar 2 2004, 08:25 PM

Posted by: djellison Mar 2 2004, 08:28 PM

Posted by: lars_J Mar 2 2004, 10:00 PM

Nice!!!

BTW - There is one relatively easy way of calibrating Opportunity color images that had not occured to me until today:
Steve Squires mentioned that the spherules were not blue, but actually gray. (roughly equal reflectance in every visible wavelength, as supported by this spectral http://marsrovers.jpl.nasa.gov/gallery/press/opportunity/20040202a/Meridiani_spectra-B009R1_br.jpg, the "dark cobble" material)

So what I did was to pick a pretty representative bright blue spherule color in your color image. The results was 110, 172, 223. ( r, g, b ) Using those figures I multipled the green channel by roughly 0.65, and multiplied the blue channel by roughly 0.5, and the image that came out matched JPL's true-color images much better. Try it out!
(BTW, this is of course a simplistic modification, since the exposure curve is not linear, so some other conversion might be better, but the result was surprisingly good)

It is kind of neat that we may have much of the calibration data we need right in front of our noses... At least if there are spherules in the image.

What do you think?

Posted by: djellison Mar 2 2004, 10:17 PM

Sensible thing is to do a 'levels' in Photoshop and eye-drop the middle grey off a spehrule.

I tried it, and you end up with an odd mixture

I've never pretended to try and make 'real' colour pictures - we just dont have the info to do that properly, so I dont think it's worth really trying.

I try to make my pictures as dynamic and feature-rich as possible, which often means not realistic.

Doug

Posted by: lars_J Mar 3 2004, 01:20 AM

(Trying out the attachement process)
Here is a small example of my "spherule-calibration"... It does at least make the trench bottom look less icy, and more like what it really is - compacted red dirt.

I do completely understand the tradeoff between realism and beauty, however.

Posted by: djellison Mar 3 2004, 09:21 AM

Yeah -it works nicely - although you'll instantly have shouts of "arhg - he's tinting images red to follow the nasa conspiracy"



Doug