IES strange intensity behavior

[Dionysios.TS]

Any news? Still  nothing... Houston?

[julobo]

I've noticed that 3dsmax photometric lights intensity doesn't change when size changes.
Corona lights do which I guess is correct behavior.
I've managed to get similar results if the size of corona lights is the same as 3dsmax light and I put the 3dsmax lumen value in the corona intensity in lux, not lumen or candela.
Not sure it works in all cases but for iGuzzini IES files, it's really close.

sorry for my english :p

[Jpjapers]

Has the 1.5.1 hotfix addressed any of the problems you had with the IES?

[Dionysios.TS]

I don't think so, unfortunately...

[PROH]

Hi. Don't know if this works with IES, but in my tests a photometric light set to a preset lightbulb matches a Corona light (sphere mode) exact when then "cd" values in the photometric light is the same number as the "lm" values in the Corona light, and everything else is set equal.

So if the photometric light bulb reads 161,0 cd and the Corona spare light reads 161,0 lm, then they will match.

Haven't tried it with IES, but maybe?

Hope it helps

[Jpjapers]

Could it be that simple... I hope so!

[maru]

Hi guys,

First of all, sorry for no replies. I don't know why it happened. I must have overlooked the topic, and also Ondra & co are very busy right now.

Could you please list all issues from this thread? It got a little chaotic, right now I wanted to report this to Ondra, but I am not even sure what should be checked. Is the original issue that 3ds Max native lights work fine (correct; as expected) with IES lights, and Corona lights seem to be incorrect?

[Dionysios.TS]

Hi guys,

First of all, sorry for no replies. I don't know why it happened. I must have overlooked the topic, and also Ondra & co are very busy right now.

Could you please list all issues from this thread? It got a little chaotic, right now I wanted to report this to Ondra, but I am not even sure what should be checked. Is the original issue that 3ds Max native lights work fine (correct; as expected) with IES lights, and Corona lights seem to be incorrect?

No worries, we know you're busy guys... :)

In a few words, many of us checked this behavior in Corona:

- Get an IES file.
- Use its lumen, lux or cd value with a 3ds Max native photometric light = intensity result is physically correct.
- Same file, use its lumen, lux or cd value with a Corona light = intensity is very low.

Result: To get the same lighting intensity we need to multiplier a lot the IES value which is not a good thing as you can imagine.

So, why Corona does this? Why it doesn't read the REAL WORLD values in a 1:1 correct mode?
We found out that also Vray has the same sort of problem and they add an option to scale the IES values for it. Probably is a 3ds Max scale bug or defect? Who knows.

Dionysios -

[karnak]

Hi maru, here my understanding of the problem.

A. They are assuming that what they see when they render a Photometric Light (IES) in Corona is correct.
B. They want to match the same result with a Corona Light (IES), but in order to do that, they have to reduce the intensity multiplier by a lot (see the image in the first post).

To further sum this up, the problems are two:
1. There is no consistency between Photometric Light (IES) and Corona Light (IES).
2. What is the correct result between the two?


Regarding point 1, I think there is a different interpretation of the numeric intensity values.
If that is the case, a simple solution would be scaling one of the two, like VRay does when you check "Use 3ds Max photometric scale".

Regarding point 2, I think the correct result is with Corona Light (IES) with proper intensity values.

I have attached a test I made a while ago.
On the left there is a real world reference (2 cheap light sources).
On the right a simulated environment with 2 Corona Light that have correct light intensity and position in space relative to the subject.
The settings and exposure of the virtual camera also match the real camera.

[Dionysios.TS]

Hi maru, here my understanding of the problem.

A. They are assuming that what they see when they render a Photometric Light (IES) in Corona is correct.
B. They want to match the same result with a Corona Light (IES), but in order to do that, they have to reduce the intensity multiplier by a lot (see the image in the first post).

To further sum this up, the problems are two:
1. There is no consistency between Photometric Light (IES) and Corona Light (IES).
2. What is the correct result between the two?


Regarding point 1, I think there is a different interpretation of the numeric intensity values.
If that is the case, a simple solution would be scaling one of the two, like VRay does when you check "Use 3ds Max photometric scale".

Regarding poin 2, I think the correct result is with Corona Light (IES) with proper intensity values.

I attach a test I made a while ago.
On the left there is a real world reference (2 cheap light sources).
On the right a simulated environment with 2 Corona Light that has correct light intensity and position in space relative to the subject.
The settings and exposure of the virtual camera also match the real camera.


ps. Hi Dionysios, I'm Matteo :)

Ciao Matteo!!! :D

Thanks for writing here in more detail everything.
I really have the doubt who has the correct results. The problem came out while I was using the Corona Sun system and an IES file in the same time. I couldn't believe that a light with  5.065cd (as noted from the manufacturer) was practically almost turned off in the scene. So I had to crunch up the values to start seeing it's effect. Then I compared both lights together, 3ds Max IES and Corona IES and I found the big difference. I work with IES files since Lighscape and I know how they should work. Something is wrong...

PS. Te come va???

[cecofuli]

As you can see in my images, the V-Ray parameter "3ds max photometric scale", doesn't do that.
V-Ray IES and 3ds Max IES have, always, the same intensity!
From what I can understand thanks to my test, is that Corona doesn't handle 3ds Max photometric intensity very well.

[karnak]

What I see is that the intensity value inside a VRayLight and the intensity value inside a Photometric Light are interpreted in the same way by the renderer (VRay). They are consistent with each other. I also see that "3ds max photometric scale" is internally scaling both values, so that the renderer can interpret the numbers in two different ways: VRay way and 3dsMax way.

What I am saying is that the intensity value inside a CoronaLight and the intensity value inside a Photometric Light are not interpreted in the same way by the renderer (Corona). They are not consistent.

If you want them to be consistent you have to internally scale one of them and match the other.

I hope this explains better my point.

[Dionysios.TS]

What I see is that the intensity value inside a VRayLight and the intensity value inside a Photometric Light are interpreted in the same way by the renderer (VRay). They are consistent with each other. I also see that "3ds max photometric scale" is internally scaling both values, so that the renderer can interpret the numbers in two different ways: VRay way and 3dsMax way.

What I am saying is that the intensity value inside a CoronaLight and the intensity value inside a Photometric Light are not interpreted in the same way by the renderer (Corona). They are not consistent.

If you want them to be consistent you have to internally scale one of them and match the other.

I hope this explains better my point.

Yes  but we shouldn't scale anything in reality. The SW should do this automatically. What happens if one day I have to use Max with system setup in Inches and another day in meters? Does this influence the scaling too? If yes, then is crazy! :)

[karnak]

internally scaling = the SW should do this automatically

I'm speaking code, you are speaking artist. :D

Anyway, we are discussing on my speculations, the important part of my post was this:

Hi maru, here my understanding of the problem.

A. They are assuming that what they see when they render a Photometric Light (IES) in Corona is correct.
B. They want to match the same result with a Corona Light (IES), but in order to do that, they have to reduce the intensity multiplier by a lot (see the image in the first post).

To further sum this up, the problems are two:
1. There is no consistency between Photometric Light (IES) and Corona Light (IES).
2. What is the correct result between the two?

I was just trying to help maru understanding what the problems are. :)

[Dionysios.TS]

internally scaling = the SW should do this automatically

I'm speaking code, you are speaking artist. :D

Anyway, we are discussing on my speculations, the important part of my post was this:

Hi maru, here my understanding of the problem.

A. They are assuming that what they see when they render a Photometric Light (IES) in Corona is correct.
B. They want to match the same result with a Corona Light (IES), but in order to do that, they have to reduce the intensity multiplier by a lot (see the image in the first post).

To further sum this up, the problems are two:
1. There is no consistency between Photometric Light (IES) and Corona Light (IES).
2. What is the correct result between the two?

I was just trying to help maru understanding what the problems are. :)

:D :D :D
As you wrote seemed each of us should do manually this. No problem with math but I just don't want to. :)

I think that now he understood everything perfectly!