1rst render: Problem with lighting

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JotaSolano
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1rst render: Problem with lighting

Post by JotaSolano » Thu Mar 04, 2010 7:29 am

Hey guys.. This is my first render with Indigo so I've had some (if no a lot) of difficulties lol...

The scene is a simple lamp, with walls and a ceiling ... the problem is that I can get the light bulb inside the light to emit light... I've already set a Specular material with a light emission of 20 000... but still nothing... Or something is blocking it...

The lamp shade is a material I downloaded from here: http://www.indigorenderer.com/materials/materials/66
It's a glass material...

I've uploaded the rendered image at 152 spp (i know it's low.. but it's a test...): http://www.sendspace.com/file/fxtlay

and here is the .blend packed file: http://www.sendspace.com/file/bzzga3

Any suggestions please?

Thanks!

JS

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lycium
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Re: 1rst render: Problem with lighting

Post by lycium » Thu Mar 04, 2010 10:52 am

Hi JS!

I've uploaded your image elsewhere so that it can be more easily seen:

Image

Here are some changes that could be made:

1. The emitter should be black diffuse, with emission.
2. It's better to not have the light source inside glass, since this makes rendering less efficient.
3. Glass should not be single-sided, it must have thickness.
4. Diffuse reflectances should always be < 80% for physical realism (otherwise light bounces around almost infinitely, giving very weak shadows and a crazy rendertime).

Hopefully that will resolve most of the problems you're having :)

JotaSolano
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Re: 1rst render: Problem with lighting

Post by JotaSolano » Thu Mar 04, 2010 11:08 am

lycium wrote:Hi JS!

Here are some changes that could be made:

1. The emitter should be black diffuse, with emission.
2. It's better to not have the light source inside glass, since this makes rendering less efficient.
3. Glass should not be single-sided, it must have thickness.
4. Diffuse reflectances should always be < 80% for physical realism (otherwise light bounces around almost infinitely, giving very weak shadows and a crazy rendertime).

Hopefully that will resolve most of the problems you're having :)

Thanks ! Just a couple of questions:

1. When you say that the emitter shouldn't be inside the glass... you mean that it's better just to have a mesh, like a sphere, emitting inside the lamp, right? (right now the light is inside a light bulb)... (cause it HAS to be inside... otherwise where could I place the light to make it look like it's coming from the lamp?)

2. The 3rd suggestion refers to the glass of the lamp's "screen" right?... (not the glass of the light bulb)...

3. I don't understand the 4th suggestion... should I lower the light power from 20 000 to.. what?... 2000? or are you talking about the IOR value?... cause I think it's set to 1.6...

Thanks again and sorry for the newby-ness :oops: lol

JS


P.S. Thanks for re uploading the image... i tried but it was too heavy to upload right here...

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lycium
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Re: 1rst render: Problem with lighting

Post by lycium » Thu Mar 04, 2010 1:54 pm

Don't worry about noobishness (noobity? noobosity?), no one - except maybe Nick - was born knowing this stuff ;)

1. Correct, just the naked emitter inside the lampshade.

2. Nope, I mean the glass of the bulb: all glass in Indigo must have thickness (except for architectural glass, which is currently in development). With the lampshade you use a single-surface diffuse transmitter material.

3. I mean with eg. white walls, they should not have something like "255" (full) reflectance or colour in the diffuse material, more like 180 or something.

JotaSolano
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Re: 1rst render: Problem with lighting

Post by JotaSolano » Thu Mar 04, 2010 3:02 pm

OMG ! I Think it's actually working (just 0.75 spp lol)... but I can clearly see all the objects !!

Thanks so much for the help!... I've learned that the mesh normals also affect the material ... so before closing the lamp shader I made the normals of the inner side point inward (toward the light bulb, whereas the normals in the outer side point outward (toward the walls). (Am I right about this normals thing?)

And about the white walls... it's also a downloaded material... so I guess is correct... i think... it's not completely white.

The while it has taken me to write this has allowed me to see the render more clearly... I think I've used too much light power (im using 2000)... I'll still post it when it reaches a decent amount of noise... currently 14 spp


Thanks again!


JS.

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lycium
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Re: 1rst render: Problem with lighting

Post by lycium » Thu Mar 04, 2010 3:26 pm

Excellent! And yes you're correct about the normals :)

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Re: 1rst render: Problem with lighting

Post by JotaSolano » Fri Mar 05, 2010 10:48 am

So... here they are..!... I know they're far from perfect but at least it's a start...

Next time i'll render it with less light power... (like 1500 or so)... cause it looks like too much light to me...

It took 30 min... which is longer than I would expect for this amount of noise... is there a way to speed up render times?... am i doing something wrong with the emitting mesh that makes it hard for Indigo to calculate faster?

A question about the normals and thickness:

What's the thickness exactly for?... cause, i think that in blender you can set a mesh to have both sides affected by a material... so... what's the difference? (i ask this cause im still using blender 2.49a and we don't have a thickness option... :evil: so we have to do it manually and it's time consuming and very boring ... when we get an Indigo exporter for 2.5... that'll be hopefully in the past).
Attachments
Lamp Test 3 tm.jpg
With camera tone mapping
Lamp Test 3 tm.jpg (382.08 KiB) Viewed 3901 times
Lamp Test 2.jpg
Original... took 30 min >200 spp (think it was about 170)
Lamp Test 2.jpg (488.35 KiB) Viewed 3904 times

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Re: 1rst render: Problem with lighting

Post by StompinTom » Fri Mar 05, 2010 1:31 pm

JotaSolano wrote:A question about the normals and thickness:

What's the thickness exactly for?... cause, i think that in blender you can set a mesh to have both sides affected by a material... so... what's the difference? (i ask this cause im still using blender 2.49a and we don't have a thickness option... :evil: so we have to do it manually and it's time consuming and very boring ... when we get an Indigo exporter for 2.5... that'll be hopefully in the past).
Thickness is crucial! A mesh describes a form by connecting vertices and faces that are infinitely thin, a hollow shell. Objects and forms in the so-called Real World are more than just shells, they have thicknesses, even the thinnest of paper. Similarly, in first year architectural drawing you learn that walls indeed do have a thickness and cannot be drawn as simple lines.

The reason why you need thickness in Indigo is because of the properties of glass/medium materials. The medium is exactly that: a volume, not just a surface. As such, it needs a boundary, which must therefore be a volumetric (read: closed mesh with a volume = mesh with thickness) mesh that will contain it.

Think about it this way: Your normals tell Indigo which way the light is going into the material. If a ray hits a normal pointing outward, the ray knows it's going into a different medium (i.e. glass) and vice versa. Your ray of light needs to know when it is going into a medium and when it is exiting a medium. Otherwise, chaos reigns. So, when you give a pane of glass, a vase, an orb of glass, such as you have here, thickness then you are essentially providing Indigo with two surfaces, one which tells the light when to go in, the other which tells the light when to come out. The distance that this ray of light travels in the medium has a direct effect on the appearance of properties such as the IOR, absorption, scattering, etc. The consequence of this is that, should there be only a single surface that tells the ray of light to go into the medium without a corresponding surface that tells it to come out, the ray of light will travel indefinitely within the medium which will lead to weird effects when it starts hitting other parts of your scene.

You are basically creating a boundary for your glass medium, which has to be a closed volumetric object.

EDIT: Creating thicknesses for glass objects is a bitch, but extruding all the faces and using Alt + S to fatten/shrink them is probably the quickest, easiest way to accomplish that.

JotaSolano
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Re: 1rst render: Problem with lighting

Post by JotaSolano » Fri Mar 05, 2010 1:51 pm

JotaSolano wrote:but extruding all the faces and using Alt + S to fatten/shrink them is probably the quickest, easiest way to accomplish that
Yeah that's exactly what I did (and then closing one by one all the holes in the bottom lol... all 36 of them :shock: )

Thank you for the class on thickness!!! ... NOW i get it... photon rendering requires to do things the "real" way

Any advice on the other thing, (rendering time)... before you said that sometimes when you don't use emitters properly, it can get pretty slow... (i know photon rendering is slower than the other kind... like blender internal...) but still... 30 min should be enough for this simple scene... or not?

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Re: 1rst render: Problem with lighting

Post by StompinTom » Fri Mar 05, 2010 2:01 pm

JotaSolano wrote:Yeah that's exactly what I did (and then closing one by one all the holes in the bottom lol... all 36 of them :shock: )
Don't waste your time: select the two rings, press F and select Skin Faces/Edge-Loops. :)

JotaSolano
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Re: 1rst render: Problem with lighting

Post by JotaSolano » Fri Mar 05, 2010 2:14 pm

Lol... that's the fast way... it's also not the best looking...

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Zom-B
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Re: 1rst render: Problem with lighting

Post by Zom-B » Fri Mar 05, 2010 2:19 pm

JotaSolano wrote:Any advice on the other thing, (rendering time)... before you said that sometimes when you don't use emitters properly, it can get pretty slow... (i know photon rendering is slower than the other kind... like blender internal...) but still... 30 min should be enough for this simple scene... or not?
Any info about your system could help here ;-)

A advice would be to keep emitting meshes "low Poly" if possible... also use a pure black diffuse with emission for this!
polygonmanufaktur.de

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Re: 1rst render: Problem with lighting

Post by StompinTom » Fri Mar 05, 2010 2:25 pm

JotaSolano wrote:Lol... that's the fast way... it's also not the best looking...
If you've got the same number of edges on either side, it works wonderfully. Depends on your edges though, doesn't work in every situation.

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Re: 1rst render: Problem with lighting

Post by StompinTom » Fri Mar 05, 2010 2:27 pm

Zom-B wrote:
JotaSolano wrote:Any advice on the other thing, (rendering time)... before you said that sometimes when you don't use emitters properly, it can get pretty slow... (i know photon rendering is slower than the other kind... like blender internal...) but still... 30 min should be enough for this simple scene... or not?
Any info about your system could help here ;-)

A advice would be to keep emitting meshes "low Poly" if possible... also use a pure black diffuse with emission for this!
How important is the pure black diffuse part? I've never used this... I always just leave it on the default 80% grey. Does this significantly impact render speed? That could be useful...

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Re: 1rst render: Problem with lighting

Post by Zom-B » Fri Mar 05, 2010 2:31 pm

How important is the pure black diffuse part? I've never used this... I always just leave it on the default 80% grey. Does this significantly impact render speed? That could be useful...[/quote]
Since pure black difuse material doesn't reflect any light your mesh works as a emitter only and you save ray bounces in the Scene...

For a small light Bulp maybe not this much a point, but for bigger stuff like TV Screens etc. this could really enhance rendering time ;)
(This trick maybe somehow is not perfectly logical plausible, but I prefer the speed up in most cases...)
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