Human eye physical camera

[palosanto]

Hi,

I'm new at interior scenes. That's probably very subjective but I need a starting point.
I have a scene with all the lights (IES and other types) at the designed intensities in lumens. No DOF needed. What would be the parameters of the camera (aperture, f-number and ISO that would give a "correct" depiction of what an observer actually would see in terms of intensity for a normal eye ? It's not a matter of my taste for a lighter or darker room but rather to give an accurate representation of the intensity of the lighting with those particular lights . The human eye will adapt to the intensity with its iris aperture with a certain f-number. What would be an accepted aperture, shutter speed and ISO speed for a normal observer ?

Thanks

[particlerealities]

I'm sure someone will have a much better answer for you, but the physical camera operates just like a real camera. Perhaps the easiest answer is to simply render out the view, then look at the histogram (Levels, as shown here - http://docs.chaosgroup.com/display/V...or+Corrections). Note that the example image in the help file I just linked is likely under exposed, or some kind of nighttime scene because the majority of the color channels fall towards the darker end of the spectrum. You'll want to make sure your image falls within the bell curve of the histogram - to much of the curve on the right (and getting clipped) means your image is over-exposed. Likewise, too much of the curve on the left (and getting clipped) means your image is under-exposed.

So long as your curve isn't getting clipped, your image is properly exposed - it's just a matter of sliding the exposure up/down (right/left) to balance out the exposure to your liking, which is likely in the middle of the curve.

The trick is knowing what the amount of lighting you're emitting in your scene is supposed to look like. For example, a classroom would be much brighter than a lecture hall. But a lecture stage is likely much brighter than the lecture seating. If you render "real-world" lighting, you're going to have to decide which area is more important, because the seating will be under-exposed if you try to render the lecture podium correctly. Thus, you have to start faking your lighting levels, or save out separate images and blend in post.

[glorybound]

Often, I used to refer to this exposure chart, however, I pretty much memorized it.

[palosanto]

this exposure chart

Did you mean to post an attachment ? I don't see a chart ...

[palosanto]

Thanks. What you are saying would be to adapt the camera parameters to my taste for brightness ... Are you saying that there is no way to set the camera so that it renders reality with the lights that are in the scene ? The thing is that the lights specs came from the lighting designer and I cannot change them. That's what's gonna by installed. So if an area ends up too dark it's not for me to brighten it since I'm trying to show them the result of their lighting decision. That's why I was hoping to emulate the human eye and see the results. Is this possible ?

[particlerealities]

It's like you said in your initial post - the human eye will adapt. A camera can't. Well, it can be adjusted, but only for a given light level. Imagine if you're sitting at your table staring at your menu - your eyes will adapt to the lower light level, unless it's one of those stupid uber expensive restaurants where they think it's cool that you can barely see the food on your plate because the light levels are so low so you pull out your phone and shine it on the menu... Anyway, if you tried to take a photo of your food while sitting at your table, but the kitchen pass-through window was visible in the shot, the kitchen will likely be way overexposed because the light levels are so much brighter. Your eye can adapt, but the camera has to be set for that particular shot. Changing the color mapping mode can help, but in my opinion, this only confuses the matter because it's no longer simulating real-world (photographic) results. http://docs.chaosgroup.com/display/VRAY3/Color+Mapping

When faced with such extreme light levels, many photographers start to incorporate H.D.R. photography, where they take multiple exposures of the same scene, then blend them in post to balance out the light levels.

The key is knowing what the intentions are of the lighting designer. You can also look at the manufacturer's website for product shots and real-world usage. Then, try to adjust your exposure settings until you're getting the same look in your renderings.

[glorybound]

Did you mean to post an attachment ? I don't see a chart ...

oops, I'm not sure what happened there. If you search Fred Parker Exposure Chart, you'll find it. I'm away from my PC for awhile.

Bobby Parker www.bobby-parker.com

[palosanto]

Thanks, I know exactly what type of restaurants you are talking about .... and they seem to be more and more common these days !
I'll try to work on your advice.
Cheers

[palosanto]

Got it. Thanks !