White values & emitter power - simple tips to faster renders

Tutorials/guides/tips on how to use Indigo and the Indigo exporters
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Bosseye
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White values & emitter power - simple tips to faster renders

Post by Bosseye » Tue Aug 06, 2013 2:27 am

Hi all,

Just thought I'd really swiftly put together a couple of images illustrating;

- the importance of correct rgb colour values with white surfaces
- the importance of emitter power and render times

Theres a lot of threads by new users (myself included when I started using Indigo!) on excessive grain, fireflies, "why does my render never clear up after 100 hours" etc etc and although half the time its the same pitfalls that trip up new users, I suspect these two issues catch people out even when they think they have a handle on the more obvious stuff. Aside from setting the correct Path Tracing (PT) method, something which is underestimated by new users which massively affects render times and quality is colour values and emitter power.

Its an easy trap to fall into (especially with sketchup when the default material is a greyish colour), to whack up the values of white surfaces so that it actually looks white in the model view, without realising the impact you've had on render time and quality. I've done it myself and wondered why it took all weekend for a render to clear up.

WHITE RGB VALUES

So as a really simple illustration of the effect of upping RGB values on white surfaces, here are some figures and an image. A very simple box room with a simple 'phong' floor and a 'thin glass' window, lit only by the default Sketchup sun. Render resolution was 1000x700 and all I changed in each shot was the RGB value of the white walls. Render time in all cases was exactly 1 minute. Results are in samples per pixel (SPP) and the speed value K

r255, g255, b255 - 10.48spp @ 121k
r240, g240, b240 - 16.08spp @ 186k
r225, g225, b225 - 21.52spp @ 247k
r210, g210, b210 - 25.43spp @ 295k

The difference is fairly pronounced when you look at the figures. Pure white (255,255,255) is rendering almost 3 times slower than a more realistic value of 210,210,210. The proof is in the image - the image on the left is noticably smoother and the image much more resolved (see the reflection in the glass).

So yeah, white values of no more than say 205,205,205 to 210,210,210 give or take and you'll find much less time taken to get an acceptably smooth image.

If you're craving pure white walls in the final image then you can play with the whitepoint values in the Indigo GUI or even get on with some Postpro.
WhitetestALL.jpg
EMITTER POWER AND RESOURCE ALLOCATION

Its tempting to assume that no matter how powerful your lights, Indigo is assigning each the same amount of processing power. Not so! A simple thing, but worth noting is that Indigo assigns more processing power to more powerful lights. In real terms this means that objects lit by, say, the sun will converge and clean up far faster than objects in the same scene lit by a less powerful emitter.

The interesting/useful thing about all this is that you can use it to your advantage - massively overscaling certain lights to ensure they get the bulk of the rendertime, then scaling down in light layers (assuming you're not using RT) to something approaching normal.

As a simple illustration then:

Light 1 on the left has a lumen (lm) value of 500,000
Light 2 on the right has a lm value of 2500 so only half a % of light 1.
The render is left to run for a minute or so and then then the gain of light 1 is dropped to 0.005 (ie half % of the original 500,000) essentially resulting in the same lm value as Light 2. Its pretty clear which light has been given the rendering priority in Indigo.
Emitterpower.jpg
Hope that helps out some new users looking for answers. If anyone notices any errors or omissions, let me know. I'm far from the oracle in Indigo, so theres a chance I may have got something wrong.

Thanks :D
Last edited by Bosseye on Tue Aug 06, 2013 4:01 am, edited 2 times in total.

Voytech
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Re: White values & emitter power - simple tips to faster ren

Post by Voytech » Tue Aug 06, 2013 3:57 am

Sticky this somewhere! This is fantastic for new and amateur Indigo users.

Question regarding emitter power:

In Indigo RT (no light layers), can the same effect be achieved by using the gain of individual emitters in the standalone Indigo window?

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Zom-B
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Re: White values & emitter power - simple tips to faster ren

Post by Zom-B » Tue Aug 06, 2013 4:00 am

Thanks for putting this together mate, really!

Now we can simply link here if new users struggle.

BTW: I hate this behavior of Indigo preferring stronger lights, its a typical idea born on the desk and not in the field.
This mechanic is a "noise-keeper" for complex scenes where you have a lot of different lights and need to render in 4k+ rez, there is not much room for 1001 LightLayers in my RAM
polygonmanufaktur.de

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Pibuz
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Re: White values & emitter power - simple tips to faster ren

Post by Pibuz » Wed Aug 14, 2013 4:33 am

Excellent!

Now there's really need for one last tut about using EXR and emitters together. Zom-B can help if you treat him well :lol: :lol: :lol: :lol:

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Zom-B
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Re: White values & emitter power - simple tips to faster ren

Post by Zom-B » Wed Aug 14, 2013 1:51 pm

Pibuz wrote:Now there's really need for one last tut about using EXR and emitters together. Zom-B can help if you treat him well :lol: :lol: :lol: :lol:
Set EXR to emit uniform with value of 10.000.000 and it gets very close to Indigos Sun brightens (varies between EnvMaps...), done :)
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vaebhav udhayanan 1
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Re: White values & emitter power - simple tips to faster ren

Post by vaebhav udhayanan 1 » Thu Feb 19, 2015 1:54 am

Ok so ive been rendering this for the last 8 hours and its only gotten worse. I havent added any textures as yet just so that i could get the lighting correct, but it looks like im not doing something right. how do i make this better? and how long does a typical render take to complete?
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