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HystericalKeyframe
01-22-2012, 03:33 PM
Hello,

Richard7666 and I have been discussing on this matter in this thread - http://forums.cgsociety.org/showthread.php?p=7223026#post7223026

So we thought that perhaps it would be the best if we created a new thread where people who are more experienced with this case can help us.

Anyhow, the main question is how to make a compromise between interior and exterior in Vray. Let's say, we wanted to make an animation of the camera flythrough, where the camera goes from outdoors inside the house and then again flies outside or something similar.
With Vray the scene gets blown out once you leave the nicely adjusted indoor scene or it gets to dark if you go from nicely adjusted outdoor scene inside some building.
From what we understand that is indeed the way real world camera's work, however I last time I watched such live action footage, camera automatically adapts in a matter of seconds and everything looks fine again.
How do we simulate that process of adaptation? is camera's exposure keyframing the right choice? would it do the trick? or do we need something more?
And what if we wanted to make a simulation of how a human eye views the scene, not the camera....etc etc?

So if anyone here is experienced with such type of scenes I would appreciate if he/she could share it with us :)

kanooshka
01-22-2012, 05:37 PM
The simplest way would probably be to achieve the look you want for the inside in one file. Achieve the look you want for the outside in another file. Then render the corresponding part of the sequence in each file along with the transition frames and in the end create a smooth transition when you composite.

HystericalKeyframe
01-22-2012, 07:20 PM
Great! Pretty good approach for simulating the way human I sees it...then we could eventually add the blown out effect lasting about couple seconds as a transition between those.

Right away this seems to me like the best way to do it, thanks!

MikeBracken
01-22-2012, 07:36 PM
I would animate the exposure. This is what happens in real life with a digital camera exposure set to automatic.

Regards,
Mike

HystericalKeyframe
01-22-2012, 09:20 PM
Thanks for your input Mike, I'm sure both methods are great in their own way, I will try to figure out which one gives better result and which one is more practical and make an average of it.

DanGrover
01-23-2012, 10:04 AM
Both of these options would work beautifully, but I think the least painful way - and the way that requires the least jiggery-pokery, assuming you're taking it into post anyway - is to render it into floating point 32-bit, in a format such as .hdr or .exr. These formats contain values above "1", so that if you rendered out the sequence as now, the outside would be blown out, but the subtle variations between the pixel brightness values remains in the file. What this means is that, in post, if you run a simply exposure effect and bring the value down, it will look perfectly fine without the horrible clipping that's usually associated with 'darkening' totally white images.

This should work with Nuke, Fusion, Aftereffects etc. This way, you only have to render once, you don't need two sets of camera information, and it's totally flexible so you can play with the speed and level of change in post.

HystericalKeyframe
01-23-2012, 12:31 PM
Wow this is getting better and better! :D Thanks DanGover for the input! Great suggestion...
But how do I know that the quality of this workflow is the same? do I get the same result with this as if I were to change the camera's exposure in the scene? Will I get more fuzziness with this or that method?...Shortly put, are those two the same type of value?

because if I don't lose on quality and the control, then this option would be by far the best, not just for this case but to me it seems to be a must for most scenes.

And how much can it go? from 0 to above 1? That would mean that I should adjust my scene until I am satisfied with the naturally brightest part of my scene(outdoors), and then once I render it in, lets say OpenEXR format, I can increase the value as much as I want, not having to worry about limits in the positive direction?
Or perhaps 32 images allow me to go below 0, in which case I wouldn't even need to adjust my scene towards the brightest part of it, but rather from any given camera position/angle I wanted?

Now, if only my English didn't suck so much :D but I hope you understand what I want to ask :)

DanGrover
01-23-2012, 01:57 PM
Wow this is getting better and better! :D Thanks DanGover for the input! Great suggestion...
But how do I know that the quality of this workflow is the same? do I get the same result with this as if I were to change the camera's exposure in the scene? Will I get more fuzziness with this or that method?...Shortly put, are those two the same type of value?

because if I don't lose on quality and the control, then this option would be by far the best, not just for this case but to me it seems to be a must for most scenes.

And how much can it go? from 0 to above 1? That would mean that I should adjust my scene until I am satisfied with the naturally brightest part of my scene(outdoors), and then once I render it in, lets say OpenEXR format, I can increase the value as much as I want, not having to worry about limits in the positive direction?
Or perhaps 32 images allow me to go below 0, in which case I wouldn't even need to adjust my scene towards the brightest part of it, but rather from any given camera position/angle I wanted?

Now, if only my English didn't suck so much :D but I hope you understand what I want to ask :)

Don't worry, your English is great!

Well, no, it can't go below 0. Afterall, the pixel values are, at their base level, values of light. And you can't get negative light, merely a total absense of it (ie 0,0,0 - black!). As such, you want to do it the other way around, really - have the exposure set to how you want it in the very darkest part of the scene, and render with those settings. If you set it, as you suggested, to the correct exposure in the brightest settings, you could end up getting black clipping - areas which are uniformly 0,0,0 and then when you try to brighten the image up, you get a smush of grey!

In theory doing this should be identical to changing the exposure, only the exposure is easier to get a specific result - ie, if you're trying to emulate a specific camera or settings (perhaps matching to a photograph, using real light values etc), but other than that, it should identical. Just make sure you don't have "clamp output" turned on under the VRay Colour Mapping menu! But no, it won't be fuzzier, not will it be lower quality.

I'd advise giving it a crack on a still, but if you want a test, try opening an .hdr file (if you have one) in Photoshop. Make sure it's a 32bit one, and then play with the Exposure value (under Image -> Adjustments -> Exposure) and play around - you'll see it in action.

HystericalKeyframe
01-24-2012, 05:01 PM
Thank you for the answers a lot DanGrover! :)
Now I understand everything.

Well basically, it seems that in any case in CG in general, you just always need to calibrate your scene towards the real world and make the rest of the scene proportional to it...and then you can use 32 bit output to adjust the exposure in post production accordingly to the particular scene.

And it seems that I messed up my logic, by asking if it can go below 0, I meant, "can I always adjust my scene to be dark enough? or there's a certain limit to how much dark my scene can be?". So from what I understand setting it to 0 would make it complete black in all cases? or it would just have 0 effect on the picture and the picture will stay as is?

Oh and I always have my clamp output turned on for some reason :D I'll make sure I turn it off :D

DanGrover
01-24-2012, 07:40 PM
Thank you for the answers a lot DanGrover! :)
Now I understand everything.

Well basically, it seems that in any case in CG in general, you just always need to calibrate your scene towards the real world and make the rest of the scene proportional to it...and then you can use 32 bit output to adjust the exposure in post production accordingly to the particular scene.

And it seems that I messed up my logic, by asking if it can go below 0, I meant, "can I always adjust my scene to be dark enough? or there's a certain limit to how much dark my scene can be?". So from what I understand setting it to 0 would make it complete black in all cases? or it would just have 0 effect on the picture and the picture will stay as is?

Oh and I always have my clamp output turned on for some reason :D I'll make sure I turn it off :D

There is a useful reason to clamp output - you get horrible anti-aliasing artifacts around very very bright areas if you're rendering out to 8 or 16 bit if you don't clamp the output. I'm not entirely sure why this is - I assume it's some internal struggle it has with AA'ing the huge values involved. But when you're rendering 32bit you need it turned off, else you're just putting 8bit data in a 32bit file!

As for your question, yes, you can always adjust your scene to be dark enough. As you say, taken to the logical conclusion, everything will be black, but only if you choose to crunch it down. Otherwise it'll darken down linearly just like you'd expect.

HystericalKeyframe
01-24-2012, 10:45 PM
Thank you DanGover very much! It's all clear now :)
And I'll make sure too keep in mind what you told me about clamp out.

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