Why would you read the papers? becauyse that is where the data is. Unless you read them (and understand) them you are in no position to comment on the issues. Go to a local university librarey, read and digest the contents of these articles, then come back. if you can't do this, I can post you the papers. if you don''t want to do this, then you don't have a leg to stand on.<br /><br />You can make algorithms to do anythign, it does not make it true. You can mathematically transform as map of the surface of the earth into the inside of a hollow sphere - but it does not make the earth a hollow sphere. That matters is the evidence, not the mathematics. That is why not all choices are equivalent. <br /><br />That is why the actual papers of martian sky colour deal with the actual observations, not the mathematical transformations which are only tools. For example the Viking paper discusses spectral radiance and reflectance of different images of rocks and the sky at different times. It compares the results with information from laboratory studies, ground tests, telescopic observation, and the use of calibration targets. They show that the radiance of the Martian sky is almost exactly the same as that of the surface, except brighter. this is what you would expect from an atmosphere that contains dust and a surface that is coated by the same dust. Their conclusion is that the Viking 1 sky colour at the tiome of imaging had a Munsell colour of (9YR)5/4 and a NBS-ISCC colour of 76-77 (light to moderate yelloowish brown. At the Viking 2 site the values were (9YR)4/4 and 77 (moderate yellowish brown.<br /><br />I chose the the dust coloured sky because the best evidence from multiple sources says this is the case. This is a reasoned and informed choice. You chose a blue sky because of what ????<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em> Arthur Clarke</p> </div>