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So what colour is Uranus really?
post Dec 13 2009, 12:39 AM
Post #31


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I tried to match color to approximately real look.
But saturation is higher than in real and reddish edges are artifacts from image processing (probably, I wasn't in vicinity of Uranus in my life biggrin.gif ).

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post Dec 13 2009, 03:29 AM
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The problem with having only one spectra is that you can get the mean colour of Uranus perfect, but that doesn't necessarily imply that you get the colour of any specific features correct.

I was thinking of something more along these lines (although this is probably too simple a model to work very well):

* Take a low res spectral cube of Uranus in the visible (say 15x15x15). assume that each spatial pixel is a sample from a multivariate Gaussian distribution. Determine the mean and covariance matrix from the data. Assume that the Voyager pictures of Uranus actually look vaguely like Uranus when you took the spectral cube (not likely I know).

* Each one of the Voyager images corresponds to sampling the inner product of the combined filter/imager spectral response with the actual spectra at that pixel. Thus a sequence of images can be considered a matrix transform for each pixel. The matrix transformation can then be written up as an optimisation problem trying to maximise the posterior probability of the spectra for a pixel versus the measured data using the known spectral relationships as a prior and a positivity constraint. This would require some sort of noise modelling (I have no idea what the noise characteristics of a Vidicon tube are). Unfortunately the positivity constraint means that it would probably require some sort of iterative solution.

* Given the estimated spectra for each pixel, conversion to RGB (or whatever format you want) is a pretty standard linear transformation.

Any thoughts? The premise is that missing colours like red (and indistinguishable colours) can be inferred from the presence of of other colours given prior knowledge of what Uranus looks like.
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post Dec 13 2009, 01:23 PM
Post #33


Well through a refractor it looks white-blueisch blink.gif
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post Dec 13 2009, 03:46 PM
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Regarding visual inspection of Uranus color through a telescope, one needs to remember that human eyes are not a perfect camera either and are in fact more sensitive to green wavelengths than blue (or, for that matter, red). Depending on how large a scope you are using and how bright Uranus looks, it may appear blue or green. To me, it looked "green", but I was looking through a puny 10x40 binocular.
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