Chaos Corona for 3ds Max > [Max] Resolved Feature Requests
Lightmeters and corona
Dionysios.TS:
--- Quote from: jpjapers on 2016-10-19, 23:04:32 ---Did you figure out a workaround? Or any consistent maths behind the problem to get it to how it should be?
--- End quote ---
Unfortunately not, I expect some news from the de team which I still never received.
maru:
Hi, this was already asked a few times, and unfortunately it seems that there is no reliable "light metering" in Corona yet. There is one thing, which might be helpful for you, depending on what exactly you are working on. Here it is...
--- Quote ----currently Corona does not offer any kind of automated way to measure light intensity at given point (like Vray light meter)
-it should be possible to measure light intensity in real life (I think it would be best to put the light meter as close to the light source as possible, although in theory this should not matter) and simply paste this value into Corona light, but the hardest part will be to keep realistic scale of the light emitting object, I think this will require some experimenting anyway
-here is an idea to read "real world" light intensity from rendered image:
1) set up scene in correct units and scale
2) set up light sources with correct size, units, and intesity
3) optionally, for best fidelity, use PT+PT and set MSI to really high value (more than 100, higher = closer to reality)
4) disable any tone mapping, (even set gamma to 1.0!)
5) render
6) read data from VFB. Interpret the numbers as "Watts per meter squared per steradian reflected into camera" - "original RGB" 1,1,1 should mean 1 W/(sr.m^2)
Maybe this process could be somehow reversed, but I think it will still be guessing.
--- End quote ---
Other than that, some more facts/ideas:
--- Quote ---Corona lights support the following units:
-W/(sr.m^2)
-Candela
-Lumen
-Lux
--- End quote ---
--- Quote ---You can paste the value which you obtain in W/(sr.m^2) from image pixel (or from your lightmeter in real life) into Corona light intensity and then change light units to Lux. But from what I understand this still requires some guessing and is more of a "workaround" than real light metering. Unfortunately it looks like a proper implementation of light metering tools will be required for this to work.
Another idea is to use native 3ds Max photometric lights as Corona supports them. You can then switch to Mental Ray and use pseudo-color exposure controls or other tools which are built into 3ds Max to get the desired light intensity, and switch back to Corona again.
--- End quote ---
--- Quote ---it seems that the easiest way to recreate real light in Corona (or any other renderer probably) would be to find what is the light's intensity in lumen (it should be on the box/package if this is some regular light bulb, or there should be some manual with such info if this is some more advanced/photographic light). If you know value in lumen, then you should be able to simply paste that value into Corona light. If you know the power of light in W, and you know the light's efficiency, then you should also be able to convert this into lumen. Here is an example calculator: http://www.rapidtables.com/calc/light/watt-to-lumen-calculator.htm
There are also some obstacles like light color, or light shape, so it looks like this is always some simplification.
--- End quote ---
--- Quote ---If you are not after scientific precision, I would suggest you taking a number of reference photos so that you would know the camera exposure values (shutter speed, iso, f number, etc), then recreating these exposure values in Corona and tweaking light source intensity so that the image is visually similar to the reference photos. Unfortunately I don't think there are currently any easy ways of doing this.
--- End quote ---
Dionysios.TS:
--- Quote from: maru on 2016-10-20, 13:27:59 ---Hi, this was already asked a few times, and unfortunately it seems that there is no reliable "light metering" in Corona yet. There is one thing, which might be helpful for you, depending on what exactly you are working on. Here it is...
--- Quote ----currently Corona does not offer any kind of automated way to measure light intensity at given point (like Vray light meter)
-it should be possible to measure light intensity in real life (I think it would be best to put the light meter as close to the light source as possible, although in theory this should not matter) and simply paste this value into Corona light, but the hardest part will be to keep realistic scale of the light emitting object, I think this will require some experimenting anyway
-here is an idea to read "real world" light intensity from rendered image:
1) set up scene in correct units and scale
2) set up light sources with correct size, units, and intesity
3) optionally, for best fidelity, use PT+PT and set MSI to really high value (more than 100, higher = closer to reality)
4) disable any tone mapping, (even set gamma to 1.0!)
5) render
6) read data from VFB. Interpret the numbers as "Watts per meter squared per steradian reflected into camera" - "original RGB" 1,1,1 should mean 1 W/(sr.m^2)
Maybe this process could be somehow reversed, but I think it will still be guessing.
--- End quote ---
Other than that, some more facts/ideas:
--- Quote ---Corona lights support the following units:
-W/(sr.m^2)
-Candela
-Lumen
-Lux
--- End quote ---
--- Quote ---You can paste the value which you obtain in W/(sr.m^2) from image pixel (or from your lightmeter in real life) into Corona light intensity and then change light units to Lux. But from what I understand this still requires some guessing and is more of a "workaround" than real light metering. Unfortunately it looks like a proper implementation of light metering tools will be required for this to work.
Another idea is to use native 3ds Max photometric lights as Corona supports them. You can then switch to Mental Ray and use pseudo-color exposure controls or other tools which are built into 3ds Max to get the desired light intensity, and switch back to Corona again.
--- End quote ---
--- Quote ---it seems that the easiest way to recreate real light in Corona (or any other renderer probably) would be to find what is the light's intensity in lumen (it should be on the box/package if this is some regular light bulb, or there should be some manual with such info if this is some more advanced/photographic light). If you know value in lumen, then you should be able to simply paste that value into Corona light. If you know the power of light in W, and you know the light's efficiency, then you should also be able to convert this into lumen. Here is an example calculator: http://www.rapidtables.com/calc/light/watt-to-lumen-calculator.htm
There are also some obstacles like light color, or light shape, so it looks like this is always some simplification.
--- End quote ---
--- Quote ---If you are not after scientific precision, I would suggest you taking a number of reference photos so that you would know the camera exposure values (shutter speed, iso, f number, etc), then recreating these exposure values in Corona and tweaking light source intensity so that the image is visually similar to the reference photos. Unfortunately I don't think there are currently any easy ways of doing this.
--- End quote ---
--- End quote ---
Maru, at this point, the problem I found by using IES files in Corona how can be solved? Lumen, cd or lux values are not working in the same way as they do in 3ds Max photometric lights which they seem physically correct.
Thanks,
Dionysios -
maru:
I do not know the answer right now. We will definitely look into this.
Jpjapers:
I started this thread a few years back, I was just wondering if there has been any investigation into using 3dsmax lightmeters?
Considering the architectural nature of the majority of users here it seems like it may be useful for those who are working in the industry.
If anyone has a more reliable workaround than the above to measure Lux in corona scenes it would be greatly appreciated!
Otherwise, i have to resort to relux and that software is horrid.
Thanks
Jack
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