Drawing a better star

Discussion forum for Celestia developers; topics may only be started by members of the developers group, but anyone can post replies.
krishnafbgroup
Posts: 1
Joined: 27.02.2018
With us: 1 month 26 days

Post #81by krishnafbgroup » 28.02.2018, 08:28

Yes fact, with glare described as a Gaussian, extremely bright stars did not look like the ones in your image. With a Gaussian, the edges of the star get sharper as the brightness increases. This matches what we see for the core PSF, but the glare behaves differently.

Here's a very relevant paper titled "Physically-Based Glare Effects for Digital Images": http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdf

The authors describe the PSF for the eye as the sum of three terms: a central Gaussian, a theta^-2 term, and a theta^-3 term (where theta is the angle from the center of the light source.) Here's a sample image of the Southern Cross where Gaussian glare is replaced by G(1/(1 + k*r^3)), where G is the glare brightness, k is a constant that sets the glare falloff rate, and r is the distance in pixels. I deliberately did not the angular distance, as it's more desirable to resolve stars at high zoom factors than it is to try and realistically reproduce all the quirks of a real imaging system (and I realize that's what I did with the diffraction spikes, but they're aesthetically pleasing :) ).

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mmontag
Posts: 3
Joined: 09.04.2018
With us: 16 days 3 hours

Post #82by mmontag » 09.04.2018, 22:28

Is anyone currently working on this? I would love to contribute to Celestia and maybe hack on this as my first entry into the void. I will be looking around the forum to try to figure out what the current state of the project is, whether Chris is still involved, etc. Is the github repository now the canonical source?

krishnafbgroup wrote:Here's a very relevant paper titled "Physically-Based Glare Effects for Digital Images": http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdf

The link is broken, but here's another copy:

http://luthuli.cs.uiuc.edu/~daf/courses/rendering/papers3/spencer95.pdf


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