IES files in nXt

[Aleksander Nowacki]

The support of IES files is one of the best nXt's properties. It's really great tool, but at the same time it's almost useless, because nXt automatically equalizes the brightness level of the scene, so there's no difference between 1 Watt and 100 Watts light fixture (see the file attached).

Roy, is there any chance to implement some global switch into nXt, that turns this method on/off to get some more realistic lightness if needed (I mean - 1 Watt light source gives really dark render without changing brightness level manually)? Or maybe some of the engines you're working on could have this possibility?

[Roy Hirshkowitz]

I've got a tone operator switch which I'm currently testing which automatically darkens low light levels or scotopic vision.  These occur when the average light levels are approximately 10^-2 (0.01) cd/m^2.  I'm not sure I'll be able to capture a lot of the other effects very easily.  For example, at scotopic levels, contrast is also reduced, it becomes difficult to resolve detail (such as text), and colors begin to shift.

Even if I did implement something like this, light levels above mesopic 10 cd/m^2 would still be indistinguishable.  For most scenes this means that lights of say 1000 watts could not be distinguished from lights of 10000 watts.  The distinctions in this range are far more subtle (after the human visual system has adapted to the light levels.)

[Aleksander Nowacki]

Thank you for the answer.

I keep my fingers crossed for some improvement of the light levels in nXt.

Alex

[Peter Milner]

If you add in a second light source such as a large area light at 50W then you will see a big difference in the light levels of the spotlight.

The other option if you're rendering in the AutoCAD window is to do the first remder and then lock the exposure (nxttoneop 1) beforre doing the second render.

[Aleksander Nowacki]

Peter,

your hints are what I've been waiting for, but please, give me more information.

Option 1

1. where this second "large area light" should be located (it's influence won't be visible in a scene, I hope)?

2. what should be the size of this object?

3. is it possible to calibrate it somehow - to gain the light levels close to the real ones?

Option 2

1. it also sounds promissing but the variable "nxttoneop" doesn't work at all (error: no function definition: NXTTONEOP)

Generaly: can you tell me what nXt engine are you using? are you rendering in Autocad window and why?

I truly appreciate your help, because your works are the best accurender renderings I have ever seen.

[Roy Hirshkowitz]

Peter is suggesting that you use more than one light and only adjust one.  The relative difference between the two will be readily apparent.

The function he's referring to is (nxtlocktoneop) -- but it won't work for what you want to do.  It's equivalent to manually adjusting the brightness setting.  It does not automatically provide "correct" levels.  Yes, if you render something at 1700 lumens, lock the toneop, then render at 17 lumens, you'll get a dark picture.  You'll also get a dark picture if you turn down the brightness.  They're equivalent.