help with cm2 factor in mia_exposure_photographic.

[djx]

When looking at the numbers you need to also consider what is the brightness of the illumination in your scene and what are those numbers meaning. If you take the mia_physicalsky as an example, the manual says
[If you] set mia_physicalsky rgb_unit_conversion to 0.318 0.318 0.318, then the final rendered pixels are true photometric luminance values in candela per square meter These true luminance values then fit perfectly as input to the photographic tone mapper.

If you do that then you would leave cm2_factor=1.
Its up to you though. I think it all depends on how you choose to claibrate your scene and whether you want the actual value ranges to mean something in relation to the real world.

-- David

[MasterZap]

When looking at the numbers you need to also consider what is the brightness of the illumination in your scene and what are those numbers meaning. If you take the mia_physicalsky as an example, the manual says

If you do that then you would leave cm2_factor=1.
Its up to you though. I think it all depends on how you choose to claibrate your scene and whether you want the actual value ranges to mean something in relation to the real world.

-- David

To be honest... outside of using the physical sky, trying to use the photographic tonemapper in "absolute" mode is pretty meaningless in Maya, since AFAIK no maya light has any meaningful units.

It's quite different in 3ds Max whos photometric lights are all in real photometric units.

You can still get all the "nifty features" out of the exposure control in "arbitrary" mode. The only difference is that your exposure is, well, arbitrary, but because your lights are arbitrary, that's a necessity.

/Z

[epq]

To be honest... outside of using the physical sky, trying to use the photographic tonemapper in "absolute" mode is pretty meaningless in Maya, since AFAIK no maya light has any meaningful units.

It's quite different in 3ds Max whos photometric lights are all in real photometric units.

You can still get all the "nifty features" out of the exposure control in "arbitrary" mode. The only difference is that your exposure is, well, arbitrary, but because your lights are arbitrary, that's a necessity.

/Z

What if we are using the physical_light shader ?
Are these values in maybe any usefull units.

[ghostlake114]

But I am using portal_light for light shader
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So in conclusion, no rule for this parameter in Maya>?

[ghostlake114]

I dig this topic up because I am enter problem with it now

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I am making a pure interior scene with no sun light, mean no need to creat physical sky. And using a standart physical camera with
iso=100,f=1/16,s=1/100

but the scene is pure dark as discuss above.

So as Master Zap said
To be honest... outside of using the physical sky, trying to use the photographic tonemapper in "absolute" mode is pretty meaningless in Maya, since AFAIK no maya light has any meaningful units.

It's quite different in 3ds Max whos photometric lights are all in real photometric units.

You can still get all the "nifty features" out of the exposure control in "arbitrary" mode. The only difference is that your exposure is, well, arbitrary, but because your lights are arbitrary, that's a necessity.

It mean we can not have any "physic" setup for this parameter.
But until now, have anyone found a setup for this parameter in this case, what unit we should use in scene, light setup in physical mode (for example physical light)...etc,so we could make a render in its "physical" thing

What I am doing is make the shutter really small: 1/0.15 and the scene get brighter, or make this "misterious parameter" into really big (1000) so I make scene bright... but doing this way, it s kind of trial and error thing without any knowledge of what we are doing :(

[tfritzsche]

...
What I am doing is make the shutter really small: 1/0.15 and the scene get brighter, or make this "misterious parameter" into really big (1000) so I make scene bright... but doing this way, it s kind of trial and error thing without any knowledge of what we are doing :(

I don't know much about the photographic tonemapper, but a f-stop of 1/0.15 is really big, not small, the small apetures are 1/16, 1/32, 1/64 etc. -these let less light in. large apetures are 1/5.6, 1/4, 1/2.5, 1/1.8 etc.. letting more light in. Your camera setup in the photographic tonemapper of iso=100,f=1/16,s=1/100 in a real world indoor scene would result in a near black image too, the iso would need to be at 1600 or 3200 for the f-stop and shutter speed to record anything useful, unless of course you have a flash:).


hope this helps

thomas

[sequenz]

To be honest... outside of using the physical sky, trying to use the photographic tonemapper in "absolute" mode is pretty meaningless in Maya, since AFAIK no maya light has any meaningful units.

It's quite different in 3ds Max whos photometric lights are all in real photometric units.

You can still get all the "nifty features" out of the exposure control in "arbitrary" mode. The only difference is that your exposure is, well, arbitrary, but because your lights are arbitrary, that's a necessity.

/Z

that is a bad news. and what if we use the portal-light, the physical light from mr? or is in maya2008 physical correctness only possible when using the physical sky?

thanx
lars

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