Hello guys, I'm trying to create some nice looking moon/star cg image
So I firstly tried an old fashioned method

1.Get a moon pole and a star map from NASA
Assign a material with moon's base color/displacement texture to a little sphere.
Assign a material with Celestial Star map texture to a big sphere, or the celestial sphere (the backdrop)

2.Add a distant light as sunlight

Then, the problem happens
Problem1.Celestial sphere blocks the distant light, and the moon appears black.
Problem2. The star map is much too bright. The empty area with out stars should have ZERO brightness, however, the default translation of the NASA star map makes the map "glowy"

So for problem 1 I tried
1.Light mask
2.Light bank
but none of these work. It seems that, these function deal with if the object is lit rather than it the object will block the light rays.


For problem 2, I know that in unreal there is a shading model called unlit so you can just use a fake star map as a color emmision map to do the star back drop. But I haven't found how to do that in houdini yet. I tried to do that with environment light, that only makes things worse, the empty areas are even brighter.

So I would like to know that is there anything to bypass this?



PS: I know that in real world you have exposure problem of optical device, so if you can see very close(astronomically) sun-lit objects,you can not see stars. But for artistic porpuse, how can we do this? I know houdini can do composition, so we can render to .exrs separetly and compose. But for best artistic result, which work flow should I try. Now lets try to add some challenge, add some volume nebula effect. Then I think at least the volume, sunlight and the moon should be in the same scene.

Try to exclude the celestial sphere from the light shadow (on the light) and on the object itself remove anything from the light mask.

Soothsayer
Try to exclude the celestial sphere from the light shadow (on the light) and on the object itself remove anything from the light mask.

Thanks for the quick answer. It works.
I guess the exclusion syntax is "^" right?

It's embarrassing..
I found how I did not make the star drop looks correct: I made the emission channel only material but I didn't assign it to the star backdrop sphere...

So I use the ramp parameter to add a chroma variation to the 8K resolution backdrop.
I'd like to hear some guide/feedback on how to improve this...It is still very primitive..

It's kind of right but doing this in render you're setting yourself up for problems with noise and sampling and such. Comp would be the way for a star map.

What he said -- I think it's fine to use a general star map when setting up the scene and doing test renders to get a general idea of what the look of the shot is, but then disable the star map entirely and do it in your favorite comp app.

I am doing exactly that at the moment, utilizing AfterEffects and this plugin called ORB by VideoCopilot which basically creates a sky sphere that I can use to map the stars to. When I bring my animated camera into AE, the stars move accordingly.

Star maps, if applied as a texture on a sphere and rendered separately, usually anti-alias just fine from my experience. What I have had problems with is proper mip-mapping on visible environment lights...