Description: Tips for creating and manipulating planet textures for Celestia.
scalbers wrote:It turns out that a simple adjustment of contrast of each color of the DSCOVR images can make them (in my opinion) better gamma corrected and thus match pretty closely my renderings.
scalbers wrote:More Rayleigh scattering should increase the blue more when looking at the center of the Earth, and near the limb it should get more greenish or grayish.
Code: Select all
SpecularColor [ 0.72 0.64 0.52 ]
Rayleigh [ 0.001 0.0025 0.006 ]
scalbers wrote:What I'd further suggest is dimming the land albedo a little bit, along with lowering the specular power for the sun glint.
scalbers wrote:Is there any implied calibration of textures to albedo?
scalbers wrote:I agree Earth's atmosphere scale height is 8.5 km, though this applies just to the Rayleigh scattering. It is usually less for aerosols (Mie scattering) at around 2km, though sometimes up to around 5km. Rayleigh scattering can be specified at sea level using about 0.14 optical depth for green light (546nm). This has a known single scattering phase function also.
scalbers wrote:As kind of a side point my images are slightly bluer than might be standard since I set my sRGB white point to be the same as the color temperature of the Sun (about 5800K). Correspondingly I set my computer monitor to this same color temperature, instead of the often used 6500K.
scalbers wrote:A square root function is a good approximation of a gamma correction upon image display that usually should be about 2.2. It seems Celestia would then assume that the Blue Marble (BMNG) data has pixel count values that are proportional to the albedo and that 255 counts is an albedo of 1.0? There is actually a spline being used and I am approximating this using a simple piecewise polynomial. This will yield different results than assumptions of a linear or square-root function in the texture.
Celestia tints all solar system objects yellowish
selden wrote:Visually, the "yellow" peak in the light from G type stars is so broad that their light actually is white to our eyes. This is even the case for most "red" stars.
scalbers wrote:With scattering it is the main gases (e.g. N2 and O2) that do the Rayleigh scattering and the aerosols (dust or haze particles) that do the Mie scattering. Clouds also are Mie scatterers, though they more often have multiple scattering.
scalbers wrote:hus the actual reflectance of various land surface types would have a bit of dependence on the geometry. Generally the land is a bit darker in the forward scattering direction and brighter with back scattering.
scalbers wrote:It could then be scaled so 0 counts is 0% albedo, 255 counts is 100% albedo, with a linear scale in between if that would work? Thus 128 counts would be about 50% albedo.
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