[Boojah]

Hello, I have a problem with the physical sun when doing a sunset image. If the sun is near the horizon it turns yellow as it should, however when it's very close to the horizon it goes completely yellow. Increasing exposure does not make it whiter, it caps at pure yellow.

The weird thing is that the preview in the render window looks correct, the sun is white when exposed for foreground objects. But then maxwell does some computing for the final image so that a couple of seconds after changing say a multilight value, the sun snaps back to yellow. This looks completely wrong because the sky goes white behind the sun (at high exposure), so that the sun looks dimmer than the sky.

How to reproduce:
In studio, start a new scene and adjust the time of day so that the sun is very close to the horizon. Point the camera at the sun.
Render
Notice that the sun is completely yellow, and that increasing exposure does not make it white.
Adding diffraction and scattering helps visualize the problem.

This is what you get:


This is a screen cap of the "preview" right after changing a value, before it shows the final image:


The images are produced using above method at default settings, with added diffraction and scattering (which does not make a difference for the problem but makes it sort of easier to see) at multilight intensity of 7 for both sun and sky.

I have isolated the problem to the physical sky, with constant sky there is no problem.
Also with a completely blown out image, the sun is still yellow at 255,255,50 when the rest is pure white.

[seghier]

are you tried to load default sky ?

[Boojah]

It is default, only the time/sun position is changed.

[seghier]

i want test render your scene

[Boojah]

There is absolutely nothing special with my test scene, so just use the method i described, it takes less than a minute to setup. I think it's better if you set it up yourself so we can rule out any possible mistakes from my side.

Thank you for your interest in this. I hope you or someone else can confirm/disprove that this is a real problem!

[seghier]

i test scene like that ; i didn't see any problem with sun color ; for this reason i asked you to share your scene to confirm if the problem in the scene or something in your computer
i test with version : 3.0.99.4

[Boojah]

Ah I see!

Studio scene:
https://dl.dropboxusercontent.com/u/248 ... untest.mxs (Edit: it seems to try to read it as a text file. Right click the link and "save file/link as")

Mxi:
https://dl.dropboxusercontent.com/u/248 ... untest.mxi

Made using version 3.0.1.0

Just hit render, and play with the multilight sliders. To really see the problem, set the shutter really low so the sky is white, and the sun will appear 1 sec later all yellow. Well at least for me anyway

[seghier]

the time in your scene 16:34 lat/lon : 40/-3
the sun is yellow ; if you want change the color to white change the time to 16:18
in reality are you see sun white in the horizon ?
change ozone to : 1 cm
turbidity coeff to : 0.02

[Boojah]

Thanks for the tips.

However please try setting for example the shutter to 1. Then tell me if the sun is still yellow, or if you get a 100% white image. With such overexposure the sun should always be white regardless of sky settings. But for me there's still a yellow dot like so:


Reference image:
http://www.rantplaces.com/wp-content/up ... y.com_.jpg
In this image, although the scene is very red/yellow, the sun itself is completely white.

[seghier]

i will try that
in the reference image the sun is yellow near the horizon . and see the reflection is yellow
the white color become from the intensity of the light
and you never get result as reality . you must make retouch in photoshop or other software to add some real effects
and the best reference is what you see with your eyes

[Boojah]

in the reference image the sun is yellow near the horizon . and see the reflection is yellow

It's occluded by clouds, lowering the intensity.
Water does not reflect 100% of the light, again lowering intensity.

the white color become from the intensity of the light

Exactly!
So in maxwell when you increase intensity or exposure, the sun or any emitter (that is not absolutely 100% one color only) should go white at some point.

and you never get result as reality . you must make retouch in photoshop or other software to add some real effects

Yeah, but we don't use maxwell to get halfway there, right? We want it to behave just like a camera.

Thing is maxwell does it just fine 99.9% of the time, it's just in this particular instance it fails. I therefore think this is a bug with sun+sky.