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Author Topic: Global illumination here we come!  (Read 9225 times)
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twinbee
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« on: March 16, 2010, 03:49:14 PM »

All my renders so far have only used direct illumination, but for ages I've wanted to implement Global Illumination. It turns out not to be quite so tricky as I thought, but rendering times certainly suffer - something around 3 to 10x slower! My main immediate incentive for adding GI was to improve my Xmas Treehouse render. I tried to make the light bulbs in that picture as large as possible to minimize the effects of 'hard' shadows, where parts of the material inside the little 'Mandelbulb pockets' are in permanent black, but it still wouldn't compare to GI. In any case, I've been somewhat surprised at how GI can improve aesthetics even for the standard sky-lighting I have used for all my pics.

GI imitates real life more closely than usual, because everything (including the object) essentially becomes a light source as light is bounced around through all the nooks and crannies. The material seems to have a 'warm glow' feel, and there are less 'inky blotches' all over the place.

Below is a preliminary comparison I made between the two approaches. To obtain the same brightness and feel of the global illumination version, I have attempted to adjust the contrast, gamma and saturation of the direct illumination picture. But as you can see, it's all to no avail, as global illumination just does stuff that DI can't hope to achieve.



Here are some other GI renders I made last night. I'm surprised at how badly JPEG compresses the deep red picture (even at 95% quality!), so I used PNG for that one.

« Last Edit: March 16, 2010, 04:19:20 PM by twinbee » Logged
David Makin
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« Reply #1 on: March 16, 2010, 04:19:47 PM »

Lycium gave me a tip for the red jpg problem (at least on a PC) - download and use IrfanView to save jpgs - it allows you to enable/disable the colour sub-sampling on jpgs, an option not normally available.
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ker2x
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« Reply #2 on: March 16, 2010, 04:24:49 PM »

woaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa  shocked


edit : btw, i have a fortran GI raytracer in my TODO list. Someday, i may be able to general fractal and GI in the same program smiley
« Last Edit: March 16, 2010, 04:33:19 PM by ker2x » Logged

often times... there are other approaches which are kinda crappy until you put them in the context of parallel machines
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KRAFTWERK
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« Reply #3 on: March 16, 2010, 04:55:16 PM »

I still like your renderings over others Twinbee, maybe because they were the first I saw.
I like the old “clay” or “plaster” feeling in your Direct illumination image, the global ill gives more of a marble feeling...

...but it is great, getting even better!
Yes, I just need to get used to it...
They are even better than the old ones!  afro
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kram1032
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« Reply #4 on: March 16, 2010, 07:09:36 PM »

the images look great but due to the GI, they lost a lot of sharpness...
Do you have some filter settings? Then you could set them sharper... smiley
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twinbee
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« Reply #5 on: March 16, 2010, 08:33:47 PM »

Quote
Lycium gave me a tip for the red jpg problem

Aha, thanks!

Quote
I like the old “clay” or “plaster” feeling in your Direct illumination image, the global ill gives more of a marble feeling...

Heh, you're like my brother who also said there was a 'small something' he preferred in the old one too. The glossy material took me a bit by surprise actually. There's almost a sub-surface-scattering look to it, and I definitely didn't program that! smiley

Quote
the images look great but due to the GI, they lost a lot of sharpness...
Do you have some filter settings? Then you could set them sharper...

That would be cheating though wink You're right, there's some blurring which is a side effect caused due to the way light is transferred between pixels. I'd like to solve it somehow internally if poss, rather than use a filter afterwards.

That's not the only problem either, you might see some dark outlines, especially near the top left of the first GI rendering. Also, unlike most other renderers, light still doesn't travel under 'bridges' etc., which is great for speed, but of course not how things should be. Until I implement that, the GI won't be perfect. Until then, I need to end up estimating the brightness of certain unseen surfaces. It's a bit of a kludge (albeit a nice one smiley )

Here's a picture where unseen surfaces are estimated at being brighter for the GI bouncing stages. Gives a nice snow effect:


* gi-snow.jpg (86.55 KB, 594x597 - viewed 458 times.)
« Last Edit: March 16, 2010, 08:55:38 PM by twinbee » Logged
kram1032
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« Reply #6 on: March 16, 2010, 09:01:01 PM »

nice indeed smiley

I'm not sure how your GI works and just naively assumed it to work like a "physically based raytracer"...
Then I remembered my time with Indigo (didn't use it in a while by now^^), where you could set different filter options:
box
gauss
mitchell netravalli (not sure if it's spelled that way, always have troubles with that name xD)
as filter type and
radius
ring
as filter settings. Default would be mn ring=1/3, radius=1/3 but you could get sharper results without really cheating on the physicalness, so to speak, if you set, I think it was ring to .5 and radius to .25 or something. Sharper than that would have introduced artifacts.
Maybe I'm totally mixing things up here, though smiley

Well anyway: Very nice shading cheesy
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bib
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« Reply #7 on: March 16, 2010, 09:11:21 PM »

Cool ! On the last picture it really starts to be difficult to distinguish it from a real ceramics molded object !
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« Reply #8 on: March 16, 2010, 11:43:52 PM »

Nice! Will your renderer be available for us to try out?

I was wondering, is there some point at which it would be easier to export fractal shots as high res meshes and import them into a rendering package?
Then you could use all sorts of techniques, like depth of field, reflections, refraction, high dynamic range, multiple light sources etc.

Or would it maybe be too hard to decide which parts of the fractal to export?
« Last Edit: March 17, 2010, 04:44:27 AM by Tglad » Logged
lycium
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« Reply #9 on: March 17, 2010, 01:47:56 AM »

nice one twinbee smiley since i work on indigo now, i should probably try adding support for intersecting the mandelbulb sometime! (though i don't have a lot of free time for fractals these days, as you guys have probably noticed)
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« Reply #10 on: March 17, 2010, 05:40:28 AM »

Personally, I do not care for what I have seen so far with the "global illumination".  The "direct illumination" is much better.  The global ones appear as if the lens on a camera is way out of focus (or I have forgotten to put on my glasses).

It even messes with the perception of the image, for example:
   
these two portions from your original comparison images shows what I mean.  In one it is clear that there are layers one on top of another.  But with the "global illumination", it looks more like a double or triple exposure, where somebody forgot to advance the film before snapping another image, overlapping the previous one.  Like ghost images.
 
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lycium
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« Reply #11 on: March 17, 2010, 05:48:39 AM »

simulating reality isn't for everyone, there will always be a place for abstract CG smiley
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Nahee_Enterprises
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« Reply #12 on: March 17, 2010, 06:36:03 AM »

simulating reality isn't for everyone, there will always be a place for abstract CG

I prefer my simulated reality to be as if I was wearing glasses and nothing appeared blurry, or that somebody knew how to properly use a camera.

Why do some fanatics prefer blurry out of focus digital images, instead of something with visible details??  Is it because they have poor eye-sight and refuse to get corrective lenses or surgery, and then feel that is the way images are supposed to look like??
 
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chaospro
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« Reply #13 on: March 17, 2010, 06:59:36 AM »

I always wondered how you actually create your images, they are fantastic! For an unknown reason I cannot recreate such images, mine keep having much less "depth-effect". Your images have "holes" everywhere, mine have just flat surfaces. If I increase the number of iterations in order to get "holes", a few appear, but then I need to apply a heavy anti aliasing in order to remove coarseness.

And regarding global illumination: Although at least currently I like more the additional details visible with the local illumination it looks excellent, too, and until now you seem to be the first person who has a running algorithm applied for the rendering of a mandel bulb. And you can do both :-)

If one now compares images with different lighting models one can see that it's not only the formula which creates nice looking images: Especially for 3D fractals proper light and an excellent lighting algorithm is essential for nice renderings.

Kind regards,
Martin

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Sockratease
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« Reply #14 on: March 17, 2010, 10:46:46 AM »

Over in "3D Land" the programs use Global Illumination too (I'm a big fan / user of Carrara, Bryce, and other 3D Software) and the same issues of Obnoxious render times arise with Global Illumination.

There are ways around it called "Fake GI" and the techniques are often unique to each program, but one Universal way is to use HDRI Lighting (High Dynamic Range Image).  Bryce calls it IBL (Image Based Lighting) but whatever it's called, it produces almost indistinguishable effects from GI and is something you may wish to look into.

I'll find some examples and post them later today...

But they don't eat into the render time nearly as much as GI does, and they have other advantages too  (they can show as a background if desired!).  Keeping details and shadows is also possible with HDRI Lighting.

I wonder how manageable an obj file (3D Model Format) of a Mandelbulb would be??  Fractal obj's can be quite large files, but Fun to play with!
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