QUOTE (4th rock from the sun @ Sep 13 2005, 10:51 AM)
Very nice images. Best Venus I've ever seen!
Here's an image I've created using the Clear and Blue bandpass filters. Not much details, but this is what you would see if you were there. General color balance is a best guess.http://www.astrosurf.com/nunes/explor/mari...mosaic_rgb2.jpg
Great work from the both of you, although I think in terms of trying to capture true color from Mariner's imagery, you're trying to make a silk purse from a sow's ear. (In terms of making great-looking non-true color images, it's a smashing success, though.)
We have tons of true-color imagery of Venus as seen from Earth, and the vaguely dirty-yellow bands corresponding to the features in the reconstituted Mariner images never appear in them.
One guess of mine is that Venus's bands show up pretty well at the blue end of the spectrum just where human S cones are failing to perform (~400nm-420nm), so that a filter with a broader response shows yellowish features pretty distinctly on Venus whereas the human eye doesn't, or just barely, can.
In general, different filter systems can be made to approximate each other pretty well when the spectrum of the body in question is nonpsychopathic. If the "dark stuff" in Venus's clouds has a really sharp dropoff around the edge of human sensitivity, then a camera/filter system that would produce results close to true color when looking at 9 out of 10 objects might go more awry with Venus.
My guess is that a person would have serious trouble seeing the relatively sharp border between yellow and white that shows up in all of these images. I will note, however, two possible alternative explanations. One is that the sharp edges are there for us to see, but are situation so close to polar latitudes that they are hard to observe from Earth. Other other is that good old glass in our telescopes performs some critical violet absorption that hides some things we would see if we were eyeball-to-cloudtop with Venus (although note: looking out of normal high-quality windows doesn't make anything I know of look funnily-colored).
Venus Express should give us the real skinny on this.