real sun/skylight

[richard_rosenman]

Posted: Mon Jan 31, 2005 4:51 pm Post subject:

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hey Richard,

great comparsion...now i have a load of questions

how did you recreate the skylight with vray? spherical gradient environment? hemispherical skydome with a vray lightmaterial, as Jeff used?

did you use logarithmic exposure correction?

how many bounces for the vray render?

The skylight is a simply blue sky color - the same RGB values as the top of the sky in the Maxwell Render.

No spherical environment, just a simple color selection in the Environment Rollout in the VRay render settings.

No logarithmic exposure - default settings.

About 20 bounces. I find this makes quite the difference. I believe the Maxwell render was also set to 20, if not 25 bounces.

And that's about it. I can share the VRay file if you guys wish - I can try to post it this evening.

-Richard

[BBullo]

Nice comparison Richard.

Amazing how close to one another they are.

This Image was created using an IES sun. It seems to bounce more light in the scene.
I had to really turn up the samples to avoid noise and artifacts, But overall I think it works quite well. This is interesting since the firs time I used Vray I was told to stay away from IES Sun and only use a target light for exterior scenes.

It looks like I will have to exeriment more with IES sun systems.




Glow was applied in PS.

[dennis]

themaxxer,

thank you, it did help abit altough i still think it is showing.
but defently alot better with it checked. have to check at a higher res.

this is without exposure control and corrected in DF.
I used lightmap as 2. thought it perhaps could throw some more sunlight around, but as most times with lightmap i think it tends to wash out the contrast.

[Trapezium]

the environment HDR of my scene is not reflected in any of the reflective surfaces of the model

I had to crank my HDRI Multiplier up to something like 10x what it wold be at normally. It would be nice if the Physical Scale parameter would do this to the VRayHDRI loader (and VRayLights) automatically. Haven't tested the built in HDRI loader yet, it may work better.

--Jon

[samuel_bubat]

Hi there,

some nice comparisions !

@Richard: Could you say something about the rendertime differences between Maxwell and Vray ?

@themaxxer: Max has an IES Sun wich is adjustable in lx not Multiplier.

@Dennis: I think fixed rate Antialiasing should prevent such problems.

But it would be interresting to know how a direct (multilpier) has to be adjusted to make it 80000 lx. Cause the IES Sun doesn´t support caustics.

And now.. what about the next challenge an animated interior sunrise
or sunset !

Another little bug I just found.. looks like the "affect background" option
of the logarithmic exposure only works in preview but not in the final image

cheers

[Morbid Angel]

Hey I just wanted to say that:
what these tests show is very close to what maxwell can do with physical sky. However these tests are very far from actual physical sky and you are all missing the point. IMHO, the point of physical sky is to just turn it on, set the date/time, and get the correct sky (with or without sun), what you all doing is starting to tweak logorythimic exposures, post process in photoshop I dont believe this is correct. I did some study on the sun and atmosphere....and its much more then just gradient ramp with a direct light.
read here
http://www.vendian.org/mncharity/dir...color/sun.html
and about atmosphere
http://www.pdas.com/atmthick.htm
And while it takes some time to mimic 1 setting in maxwell...it doesnt work for all periods of date/time...
thats why there is spectral sky...

[percydaman]

No I dont think we've really missed the point. This is more like a "yes we know our renderer cant do it out of the box, but we like a good challenge" sort of thing.

[tom schuelke]

Thats it Morbid angel brings it to the point


Yes , i tried it, and you acheave increadible nice results in this new renderer only by some mouse clicks. of course dont ask about rendertimes, but just turn on another time in your scene, and you get unbeleavable relistic sunrises or in the middle of a day, real sunny feelings.

now whats the problem but speed. (and artistic possibillities to acheave unrealistic renderings )

in my opinion there is one big question left.

Calculations inside maxwell seem to be much closer to physical behavior as we would expect from vray. this makes settings easier and faster.

But how does a physical value gets transformed on a pixel on the screen. ?
here still some sort of automatic exposure control seems to be done from maxwell, and no one allready knows if this is allright.

I would like to know if maxwell bases on any statistical analysis, how screenimages fit the best to realworld thinking of the way humans see.

if not, the exposure still is some sort of guess what fits best, because the screen still cant show real wavelength and real brightness of physical world.

nevertheless, the results somhow seem to be brilliant for the cost of rendertime, and i think its worth going on to look for this new aproach.

Tom

[percydaman]

heck this could just be another watershed moment in computer graphics. Nobody could really use GI much in the past due to its slowness and computer hardware/software at the time. But look at us now. Maybe maxwell is just a tad ahead of its time and we just need computer hardware to once again catch up to software.

[Da_elf]

im sure someone can create a script that would alter the gradient ramp depending on a time of day perameter.

[plastic_]

yeah...the thing is, if i find a way to get close to that maxwell physical sky thing with with vray, if i find the formula, i will script a UI similar to maxwell's dialog, and it doesn't matter how many exposure modifications etc. are active under the hood, because they wont be visible.

it's an emulation, but if its 99% there i'll be happy.

[samuel_bubat]

@MorbidAngel:Thank´s for these links. Very helpful !!

Well for my part a physical correct sunlight look is worth much more
than adjusting a sun by day and time because

1. If morning, highnoon or evening. It´s just the color and intensity that changes (below the line). All of this can be adjusted by the color and intensity of sun and skylight . We are artists. Do we want a sunlight system dictating our lighting ?
I want control
And I think if you make yourself some presets for different daylight situations with and IESSun,high environment multipliers, and pre adjusted
Log. Exposure vray is even easier to handle than Maxwell where you have
to guess the position of the sun to get a specified lighting.

2. My customers usually want a specific light situation. They don´t care
if it´s physically correct or not. Sometimes the lighting is finished
and they want it more yellowish, more white or a little change of the position etw. This is not easy to tweak if everything is physical correct. If my customer wants a specific lighting i can´t tell him that´s impossible because it would be physical incorrect. Can you ?

3. As you pointed daylighting is quite complex so..
How often do sunsets for example look similar. The light situation
is different every day depending on pollution, haze layers, clouds,
the alltitude you are , the region in the world and the temporary condition
of your eyes.
Does Maxwell take care of these factors ? I doubt

I can imagine some situations where a sunlight system can be helpful.
At least it should offer you any possibility to make fine adjustment
in color brigthness and light position. (Wich makes it physical incorrect)
But in my opinion this is a tool for scientist and not for artists !!
Nice to play around with.. but useless for my kind productions.
The sunlight look is all I (and probabely most other users) need. vray does a very good job with IES Lighting and Exposure !!
I really think that point goes to Vray

cheers

[tom schuelke]

Hmm,

Yes i also would like total control, but now we still have to consider that this renderer is in very early stage. So more might come soon or later. And the immages it produces are realy great as far as i could see.

on the other hand, speed counts, and like samuel said, impossible wishes of customers, you know those:

i want the diamant to bee seen clearly in a black environement without direct light and bright things....

here vray clearly wins (like others do).

da elf: a script would be great. but more than just colrshifting it also had to consider differing energylevels at each part of the skydome it produces. this is what makes up a real skydome.

but lets see what near future brings

Tom

[Morbid Angel]

Tom, I agree. I came to the conclusion that maxwell is a render before it's time. If you think on it, in production or when you are in the pipe, and you are under tight deadlines you cant possibly rely on maxwell for it's speed. Thats because our cpus are too slow for it to this day. But imagine down the road...10 years from now (ofcourse if nuclear war doesnt happen)
when we will have something like a neuronet processors (which are in development) thats when maxwell will rool. You can ask tho, well if maxwell will render fast on those then vray must be realtime...well...thats why we love vray anyway

[percydaman]

(ofcourse if nuclear war doesnt happen)

of course there IS that problem. That would put a crimp in my style