[X] My Assistant

[karolp]

Photos from the Voyager era show it to be on the border of blue and green, particularly greenish in some of them. On the other hand, amateur astronomers report from their backyards a definite "blue blob". So what colour would Uranus appear to human eye? Was the greenish tint made up as a distinction from Neptune? Or was it some flaw in image processing?

[JGodbaz]

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.