Emission Scale in SkIndigo 3.0.15

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Whaat
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Emission Scale in SkIndigo 3.0.15

Post by Whaat » Fri Oct 14, 2011 4:12 am

Here are some guidelines for using emission scale in SkIndigo. (questions taken from the 3.0.15 thread)
Pibuz wrote: 1. what is emission scale?
It is similar to 'power' in that it controls the 'brightness' of the emitter using real-world values. For example, the emission of most light bulbs is printed on the box in lumens.
2. what is the numeric value of the emission scale of sun and sky?
I'm not sure....if you take a look at the Render Log in Indigo when using Sun and Sky, it does show what luminance values are being used for the environment.
3. why a default emitter material is set to 1750 lm by default?
This corresponds to the previous default in older SkIndigo versions of a 100W bulb with an efficacy of 17.5 lm/W. To get lumens, multiply efficacy (lm/W) by number of watts.
4. how do I work with the emission scale parameter? I thought that parameter was introduced to make each light layer's calculation more handy: if I set same emission scale scale to two different materials, the one which has more power takes more CPU power. Is this correct? But..
Try not to get overwhelmed with emission scale. Just think of it as a multiplier for the emission. Using layers is recommended for greater control. It is true that more samples are given to emitters with greater luminance so a useful trick for getting emitters to converge faster (when combined with sun/sky) is to crank up the emission scale value so that it is similar to the value for sun/sky and then scale it back down using the light layer gain control within Indigo.
5. where do I set the power of the emitters? Where is the gain parameter gone? does it still matter?
Hopefully I have already answered this indirectly. :) There is still a gain parameter when setting up a blackbody spectrum but I think Indigo over-rides this value using whatever emission scale you have set.


A tutorial on this subject is would definitely be helpful. I have attached a sample SKP scene that should help a bit.
Attachments
emissionscale.jpg
40W (500lm) and 200W (3500lm) bulbs
EmissionScale.zip
(131.22 KiB) Downloaded 367 times

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Frutiger
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Re: Emission Scale in SkIndigo 3.0.15

Post by Frutiger » Fri Oct 14, 2011 4:58 am

Whaat, you're the best!

I seem to remember seeing a "lumens per square meter" unit somewhere. Does that unit actually scale the emitter's brightness based on how much surface are it covers? Or am I making that up?

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Pibuz
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Re: Emission Scale in SkIndigo 3.0.15

Post by Pibuz » Fri Oct 14, 2011 5:27 am

Thanks!

This partially clears up a little bit some of my confusion...

I thought the introduction of emission scale happened only to control the light layer "calculation precedence": if sun/sky was emission scale 1 and my emitter was 20, then a major part of CPU power would have been reserved to the second layer. That's why I asked what are the actual values of sun/sky emission scale, and that's why I asked for the gain parameter. :wink:

Thanks Dale!

..I'm waiting for your emitters tutorial, nonetheless :lol:

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Whaat
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Re: Emission Scale in SkIndigo 3.0.15

Post by Whaat » Sat Oct 15, 2011 4:10 am

Frutiger wrote:Whaat, you're the best!

I seem to remember seeing a "lumens per square meter" unit somewhere. Does that unit actually scale the emitter's brightness based on how much surface are it covers? Or am I making that up?
Yes there is a lumens per square meter and (although I never use it) I would suspect it would function as you suggest.

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