Re: [Celestia-developers] Re: Saturn texture

[Fridger S. <fri...@de...>]

Grant, Selden, Pat,...,

Preface;-)
---------

-- Yes I do work with 32bit color on my Laptop

-- I presume that neither Grant, nor me, nor Bjorn Jonsson presently know
   for sure the (precise) colors of Saturn, in the southern hemisphere  
to be specific.
-- While I used to be a devoted HST-color believer, my trust has weakened
   considerably since the HST-"truecolor" Mars has changed color so 
dramatically.
   See my long thread in the forum some time ago!
-- Like Bjorn Jonsson, I have observed Saturn for decades with an 8" 
telescope
   that is virtually free of any color aberrations.

Proposition:
------------

-- As a starter, I have compared the HST-Heritage Saturn photo with the
   default Saturn of Celestia, using the default solarsys.ssc here:
  
   http://www.shatters.net/~t00fri/images/sat-comp.jpg

   We can see quite a few marked differences!

   a) The darkness (high transparency) of Saturn's A-ring (bottom) which was
      most carefully reconstructed by Grant from earthbound data and which
      matches the recent Cassini imaging very well, is in /marked 
disagreement/
      with this "highly praised" HST-Heritage "truecolor" photo (top)!

      So why should I believe the rest of the HST image??

   b) Despite Grant's previous claims, the wide "sulfur yellow" band 
centered
      around the equator in the HST-photo is NOT identical to its default
      appearance in Celestia. In case, you cannot see that difference with
      your naked eyes, I have carefully measured and compared the central
      portion of that band with Photoshop. Using the preferrable CMYK color
      model, the yellow band is 0-2% C, 0-2% M, 15% Y, 0% K for HsT while
      the Celestia image gives 19% C 17% M 32% Y, 0%K!

      The virtually /clean/ Y color visible from HST, I definitely confirm
      in my countless telescope observations! In short, I can live with the
      yellow HST band but find the Celestia band inadequate. Even though
      Bjorn Jonsson gives an "impressive & brilliant explanation" for his
      work...Again, my preference would be to use a clean photo reference
      (either HST or Cassini) rather than this amazing blend of BJ, 
involving
      Viking 1,2, HST, & his telescope...

 [ c) Just as a non-serious  aside: the recent title photo of S&T does
        NOT show BJ's but OF COURSE Cassini's Saturn...]

-- Now (finally) I come to what I would have done already, if I had access
   to my usual image maipulation equipment and good Internet connection:

   I would use the R,G,B Saturn close-ups from the Cassini raw-data archive
   and compose them into a color image with the following /two/ constraints
   that largely fix the relative normalization of the three grayscale 
textures:

   i) The marked HST yellow equatorial band is to be reproduced precisely.
  ii) The darkness of the HST equatorial band is to be reproduced precisely.


   Then I would inspect the resulting colors in the southern hemisphere!!
   Pidgeon-gray-blue (HST) or yellow-orange (Cassini)?? That's the 
question...

-- Last not least, I agree with Grant that we should try to optimize
   haze colors etc in Celestia first!

Bye Fridger


Grant Hutchison wrote:

>>Unfortunately, on my systems (at work and at home), Celestia's lores
>>and medres texture images seem to me to be quite desaturated.
>>For example, Saturn looks almost white in the recent screencapture
>>I made of Saturn's ring shadows. See
>>http://www.lns.cornell.edu/~seb/celestia/gallery-001.html#5
>>and compare the two adjcent pictures. (I'll agree that the one
>>on the right, using an older surface texture, is much too orange.)
>>    
>>
>This certainly matches my Celestia view - unfortunately in your view Titan
>is blocking the central, yellowest part of the equatorial band, and allowing
>us to see only the marginal areas most strongly influenced by Celestia's
>blue haze - which to my mind has now been distinctly overcooked in an effort
>to match the colour-enhanced Cassini images. The result is that yellows and
>browns are markedly desaturated towards the planet's limb when viewed in
>Celestia.
>[Shrug.] So I'm saying it's a good texture and a bad haze.
>
>Grant
>
>
>
>
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