Vray Sun/Sky - Photo Comparison

[paulison]

Interesting comparison. One thing I was thinking after talking to a painter recently is that maybe the "white"card isnt actually 255/255/255. In the photo'a the white looks to possibly have a bit of grey in it which isnt noticable so much in the areas where the sun directly hits the card, but it effects the shadowed areas. The painter told me that they add a few drops of black into white paint...apparently makes it a longer lasting finish or something, so in addition to what everyone else said, the card may actually be something like 250/250/250. Everything i've said could be a complete load of crap though!

[3ddesign]

paulison,

You are right. I originally used a value of 240 240 240 for the white cardboard but after Vlado's comments, I lowered it to 225 225 225 and it is rendering much better. I also compared the original white board I used to build the physical model to a very white paint chip and the board is quite grey, about the same difference as 225x3 vs 255x3 I see on the monitor. I think I'm getting close.

Craig

[samuel_bubat]

(This post is not an offence against the author.. it´s just my general
opinion about physical correct rendering.. once again )

I still don´t get it why people are still making their life so hard by trying
to do everything physicaly correct. This is at least the 5th post I read were people are having problems to recreate their photos with physically light models. It depends on so many factors.
Each camera has a different color curve. Different white balance. The sky itself can differ very much from day to day.. and from the part of the world you are currently located. You would need to measure every single material.. to make it physically correct. Let´s face it.. a physically correct rendering simply doesn´t exist.... the only physically correct thing that makes sense is a physically correct light distribution.

It´s completely pointless. For example... if you look at some image you rendered and for some reason you don´t like the sky..
let´s say.. it´s to dark. Do you think for yourself.. "it´s to dark".. or.. "there is to much ozone in it".
We as 3d Artist don´t have all these limitations photographers have .
So why should we make this huge step backwards and bind ourselfs to all these limitations that just exist in real world. Why should I adjust my exposure in something abstract thing like F-Stops if I can have gain/gamma/saturation. Why should I mess around with ozone and turbidity if could just use a gradient were I can adjust every color as I like it. Are we artist or physicist ??
Well.. and I´m sorry.. if someone is not able to make a sky with a simple gradient... he won´t come to far with ozone/tubidity.. and the other cool words.

upss.. did I really just say all of these things ?

[3ddesign]

Samuel_bubat,

I think you miss the point entirely. I'm not trying to make physically correct renderings, just visually correct ones. Nearly all my exterior work is 3D / photo composits and my goal is to try to make them look seamless and real. I've used many different methods over the years to obtain my goal. I'm just trying to see if there is a better tool available for me to get there and posting my findings so others don't have to recreate the tests. I value the constructive comments given and I'm sure others benefit as well. Who benefits from your redundant spoutings? (two more cool words) :P

Craig

[3ddesign]

In my continuing tests, I haven’t had too much success with the Vray Sky. I just don’t have enough control over its settings (or just don’t know how to use it, which is more likely). Until I get more familiar with it, I’ve decided to show a well used approach just for comparison. Since the Vray sky is simply an educated guess at a typical sky we can guess as well. For this rendering I added a plane representing the clouds and sky and added a light blue VrayLightMTl set to 40. I had to crank up the blue to compensate for the Turbidity of the sun which can’t be set lower than 2. Where I work, in the US Western Mountains at 4500 feet, there isn't much Turbidity at all so it would be nice if that number could go lower. Also, I tried several times to get the shadow of the cube to be as light as the photo, but each time the whites blew out. Darkening the white texture didn't help. Comments and suggestions would be great. (Note that I turned the model 90 degrees to avoid sun-glare on the lens and sheen on the foamcore.)

Photo - Taken at 12:00 noon on a 50% cloudy day, camera WB set to daylight. Shutter 1/500 f10 ISO 200

Render - PhysicalCam shutter 1/500 f10 ISO 200. WB set to Daylight. Light Turbidity 2, Intensity Mult 1.0, Size Mult. 5. Sky plane to represent clouds: VrayLightMtl at 40, color at R187 G235 B255.

Photo


Render

[percydaman]

(This post is not an offence against the author.. it´s just my general
opinion about physical correct rendering.. once again )

I still don´t get it why people are still making their life so hard by trying
to do everything physicaly correct. This is at least the 5th post I read were people are having problems to recreate their photos with physically light models. It depends on so many factors.
Each camera has a different color curve. Different white balance. The sky itself can differ very much from day to day.. and from the part of the world you are currently located. You would need to measure every single material.. to make it physically correct. Let´s face it.. a physically correct rendering simply doesn´t exist.... the only physically correct thing that makes sense is a physically correct light distribution.

It´s completely pointless. For example... if you look at some image you rendered and for some reason you don´t like the sky..
let´s say.. it´s to dark. Do you think for yourself.. "it´s to dark".. or.. "there is to much ozone in it".
We as 3d Artist don´t have all these limitations photographers have .
So why should we make this huge step backwards and bind ourselfs to all these limitations that just exist in real world. Why should I adjust my exposure in something abstract thing like F-Stops if I can have gain/gamma/saturation. Why should I mess around with ozone and turbidity if could just use a gradient were I can adjust every color as I like it. Are we artist or physicist ??
Well.. and I´m sorry.. if someone is not able to make a sky with a simple gradient... he won´t come to far with ozone/tubidity.. and the other cool words.

upss.. did I really just say all of these things ?

its far from pointless. Personally I'd been thinking of doing the exact same thing. Why? So I could get a better and more precise understanding of how vray's sun and sky works. I like to know how things happen and why, its just my nature. Does it mean Ill be working to make all my future renderings completely photoreal? Far from it.

I don't care to be a physicist, I just want to understand my tools better. Think of it like a painter experimenting with how his pigments look in different lighting setups, and mixing different pigments so that he better understands color.

[RErender]

For the shadow issue, in the photo, is there something bouncing light back from the right?

[3ddesign]

Rerender, you beat me to it. Yes, I realized that there is a building off to the right, and though it is quite a ways off, obviously has some influence. I've built that into the model rendered below.

I also realized that I was making a big mistake. I didn't account for the sun being blocked by the clouds so left the intensity multiplier at 1. I figure that the clouds are blocking, maybe, half the light so dropped that down to .5. I also wanted to give Vray Sky one more shot. Since the sunlight was cut in half, I knew I had to give the sky more kick. Vlado mentioned in another post about putting the Vray Sky in an output map. Since I don't know too much about it, I just started moving sliders and adjusting numbers and fell upon a combination that worked very well. I really have no idea what I did so have posted the output map so people could explain to me what I did. Whatever the case, I am getting closer to matching reality. What's amazing is that the camera settings and the vray camera settings are identical. To me, that was pretty cool.

[Dynedain]

You're getting pretty close there.

Oh, and the 255/255/255 issue is why on sets and such, they'll use neutral gray in addition to white for calibration purposes.