Re: [Celestia-developers] Multiple light sources

[Chris L. <cl...@ww...>]

> Chris:
> > Perhaps a logarithmic approach would be better.
> I'd vote for a logarithmic approach. Over wide brightness ranges we seem to 
> have a logarithmic perceptual response ... the magnitude scale of Hipparcos 
> (the ancient Greek astronomer, not the satellite!) was perceived as 
> indicating equal increments of brightness, but turns out to be logarithmic 
> in terms of energy. But over small brightness ranges we have a quite linear 
> response (being able to roughly quantify a range of greys arithmetically, 
> for instance). So it makes sense to me to use logarithms to display the wide 
> range of real-world brightnesses within the limited, linear brightness range 
> of a computer monitor.

My preference is for the logarithmic approach as well.  I think I'll 
calibrate it so that Earth-shine on the night side of the Moon is just 
barely visible.  I believe that the Earth would be roughly magnitude -16 
in the Moon's sky.  Since the Sun has an apparent magnitude of -26 at 1au, 
this means that Celestia will be compressing a range of brightnesses from 
0 to 10^4 to the 256 levels displayable on a computer monitor.  For the 
future high dynamic range/floating point framebuffer mode, this doesn't 
apply.  Pixels will be written into the frame buffer with unmodified 
values and the scaling will be done in a tinal done mapping post process.

--Chris