Exposing VRaySky properly...

Howdy all you newborn 1.5ers!

I’m having some difficulty with the new VRaySun+Sky setup. I’ve been running some tests to get a template scene set up, however no matter what I do I can’t seem to get the VRayPhysicalCamera to expose my scene and the sky environment accurately.

I’ve taken a new scene, merged in a tower from a previous project, overridden all materials with middle (128) gray, put the VRaySky map in the environment slot, created a VRaySun and a VRayPhysicalCamera (settings below). For whatever reason, when I set the shutter speed to 500, the building exposes well but the sky is too dark. If I set it to 200, the sky looks right but the portion of the model in the sun is wayyy burned out. Can someone perhaps shed some light on what I’m doing wrong?

Thanks guys. Here’re the settings!

http://www.shaundon.com/ext/vrsun\_vray\_settings.gif
http://www.shaundon.com/ext/vrsun\_camera\_settings.gif

Shaun

Hey Shaun, i think you need to un-tick “affect background” in the colour mapping.

Wow. That’s interesting. I unticked Affect background and rendered it at 500 exposure -- the building did not change, however the background went from deep blue to pure white.

Also, the background rendered at the same deep blue color as before in the LC and IR passes. Then went pure white in the render.

Weirdddd…

Shaun

I’m testing the same thing myself right now, I think what needs to done is turn the sun multiplier down (0.2?) and then change your shutter speed to a longer exposure time (number goes down--500 to 30?). Still testing.

Vlado did say in this thread that you can do that, however the sun value will no longer be in real-world scale, so you can’t expose it with other real-world lights predictably. Which isn’t the end of the world, that’s how it’s always been, but the real-world exposure is what makes the VRayPhysicalCamera so exciting!

Shaun

I had the same problem yesterday. What I did was put the vray sky into
Max background slot. Then I manually changed the sun settings in the vray sky map. The map in my Vray environment is not the same one
(not instanced) as the one in the max environment slot. It worked great.
Really looks like a real sky, minus the clouds of course.
Hope this helps.

Maybe Vlado can weigh in on this? I don’t understand why everyone is having to use workarounds to make the VRaySun+Sky do what they were designed to do… I know I could make it work with a combination of multiple sky maps with manual controls, but I’m interested in understanding how to make the system work as it was designed to.

Thanks guys,
Shaun

You want the exposure mapping to affect the background, as it’s really part of the rendering when you’re using the maps.

http://www.chaosgroup.com/forum/phpBB2/viewtopic.php?t=16078&highlight=

The last post was a test I did using the sun/sky system. You really have to think of it in terms of real-life photography, and adjust the f-stop, shutter speed, and film ISO. For instance, on a sunny day most people would recommend 100 iso film… You’ll have to adjust all these settings as you move the sun around, a shot taken with a twilight sky will need a slower film speed and/or a slower shutter.

So, for instance, we’ll start out with the camera set at f = 8, shutter = 500, and film speed = 200.
Changing the shutter speed only x2 (from 500 to 1000) cuts the amount of light let in by 1/2 (making the image more dim).

Changing the f-stop only (from 8 to 11) does the exact same thing, reducing the amount of light by 1/2.

Changing the film speed only x.5(from 200 to 100) does the exact same thing, reducing the amount of light by 1/2.

In the opposite direction:
Changing the shutter speed only x.5 (from 500 to 250) increases the amount of light by 2.

Changing the f-stop only (from 8 to 5.6) does the exact same thing, increasing the light by a factor of 2.

Changing the film speed only x2 (from 200 to 400) does the exact same thing, increasing the light by a factor of 2.

You could probably walk out on a clear, sunny day… put your camera in fully auto mode, record what it recommends for the exposure, and plug those into the camera and they’d be pretty close.

Also make sure you have a ground plane, I think that helps with any stray GI from the sky map. Incidentally, if you’re using linear workflow, 128-128-128 greyscale is pretty light and gets blown out on tests I do, even when the lighting looks correct with actual materials applied… you might want to make a bitmap that’s 128-128-128 (at gamma 2.2) and use that on the material as a test material.

On second thought (after writing this whole thing) looking through your post again it’s probably is a problem with using linear color mapping… my test on the other page was done using linear workflow, with Gamma Correction color mapping and inverse gamma set to .454

Perhaps this will work for you…I was researching basic photography and came across a “Sunny 16” rule. Simply put, on an outdoor scene with a clear sunny sky, set your f-stop to 16. Then you shutter speed should be the inverse of your film ISO. It’s worked well for my tests, but see how that works for you.

ME

So if you are doing a sun calc ani do you need to animate the fstop?

just like you’d have in real life, yse

That’s the downside of physical correctness…it brings back all the hassle we were glad to drop when going digital

Now (sorry slight highjack here) one thing I am already missing is light metering. In my old Richo I had a light meter that showed correct fstop/apetures. My generic rule of thumb was to keep the apeture as low as possible (1/64-1/32 depending how shaky my hands were and light conditions). This gave me a range to set my image to but I also knew what I was exposing. Right now I feel like I am exposing a complete scene not directing light where I wanted it to go which was really the joy of the ol’ 35’s.

Is there any talk of a camera UI with target, focus and light metering? Or is this real time rendering stuff that I wont be seeing for a while?

Thanks for the ideas, guys. I’ve had to shelve this until next week while I prep weekend renders for an animation I’m working on.

I’m an amateur photographer, so setting exposure is nothing new to me… I just cannot fathom why it would expose a middle gray building at 80% white in sunlight, yet render a dark dark dark blue sky (which is obviously not putting out correct GI, as the shadow region is too dark.

Anyway, just came across an ugly glitch in my animation which I’m gonna go write another post on! Oh happy Friday!

Thanks again,
Shaun

sorry for bumping this thread but this is the only discussion talking about the sunny f/16 rule.
http://www.photomigrations.com/articles/0403200.htm
I’ve been playing around with the physical camera/sun/sky but when I apply the sunny f/16 rule I get very dark results.
At f/16, shut. Sp. 1/800, ISO 200 the result is underexposed, cranking up the gamma to 2.2 in color mapping and setting shut. Sp. to 1/100 gives reasonable results…
How did you get good results?
What am I doing wrong, or is the physical sky as physical correct as it should be?

In fact, the physical sky in RC3 is about twice as dark as it should be (the sun is ok though). This is corrected in newer builds, where very special care has been taken to ensure that the sun/sky/camera/lights behave correctly (well, at least as correctly as possible).

Best regards,
Vlado

ah, thanks Vlado,
I can take that in to account, I just have to make my own rule then
Will the orange coloration at the horizon be toned down in future versions? I’ve got the feeling that it becomes to dominant in the scenes as it gets closer to sundown and daybreak.
Another question, will the vray sun be made in to a sunlight system in a future version of vray? right now I’m linking to a MAX sunlight system, but the result deviates from real world situations.

In newer builds, you can select the VRaySun as a sun type from the Daylight system drop-down menu. This can automatically add a vraysky too.

Best regards,
Vlado

great
But I’ll keep my stable RC3 running for now

As for the sky, it has been tuned a bit in newer RCs.
I particularly love its (new) colours, but i’m not sure (this is definitely Vlado’s call) it’ll stay just like it is now.

Lele

I can imagine that the evening sky (or morning) would look different for the UK or for a country near the equator just because of the way the light travels through the atmosphere, that’s why it would be great when the vraysun/sky are a real sunlight system and based on real world conditions.