Digital humans the art of the digital double
Ever wanted to know how digital doubles are created in the movie industry? This course will give you an insight into how it's done.
# 106 21-05-2006 , 01:24 AM
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:p

no, its because everyone's complaining that "You have to wait for 3000 mutations per pixel to get a clean image...". Unfortunatly, 3000 mutations per pixel is a LOT of time. My interior scene is about 500,000 polygons. I got to 1500 mutations per pixel in 14 hours. With Photoshop's De-Noise filter, it almost looks clean. (almost) is a keyword.

Now, Path tracing, Bidirectional [path tracing], and Metropolis Light Transport are all rendering algorthims that use Monte Carlo aproximation (random samples, averaged. Enough samples and the average will converge to the right answer).

Path Tracing traces rays from the eye to the light (this is completly efficient and correct, since it is the EXACT mirror of what happens in real life). Unfortunatly, Path Tracing is bad with caustics, since the light has to be refracted throguh a refractive material or reflected off another into a light to work. That is why caustics with path tracing are very grainy.

Bidirectional Path Tracing traces a ray from the eye to the light, as well as one from the light to the eye. Thus, it can simulate caustics much better than stand-alone path tracing. It can be slower, though, since it does two algorithms instead of one at the same time.

Metropolis Light Transport is a very complicated algorithm that takes an existing path, made by bi-dir or single path tracing, and changes its direction randomly. Then, if this change is OK, (eg, it doesn't pass through a wall), then that new path is traced, and the result added to the average. This way, if we take a complicated situation, such as a light separated from a room by an infinite wall with a tiny hole, once the Metropolis algorithm finds this hole, it will expand and explore the hole, and the stuff behind the wall. This kind of situation is almost impossible for a Path tracer or a bidir-path tracer alone, since each new ray is completly random.

The MLT algorithm won't work very well if that infinite wall had 2 holes instead of one. It would explore one, and it wouldn't try to find the other hole, since it already found one way and needs to explore it. Thus, the lighting result would be incorrect, since the second hole would be [almost] ignored.

All of these algorithms are "Unbiased". The only incorectness in the estimation of the renering equation will show up as noise. Leave it on enough and the aestimate will converge to the right one.

There's your crash course in Rocket Science, Mirek! user added image


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# 107 21-05-2006 , 01:35 AM
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you B...D, now I'm more confused, a little more wiser but a lot more confused.

cheers my freind, good try but I have a tin head with no brain and live in the land of Oz.

i'll come back to this in say..?? 1-5 years, wouldn't yu say?? Great to read though and your explaination has made it clearer why the depth of investigation into,err, ray tracing ect. I'll keep it as a word file and use it as needed when I'm curious what boxes i should be ticking in globals and what I am actually doing. actually all I've seen in globals is 'ray tracing' are the other tracers there or are you using a differant renderer than maya?


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# 108 21-05-2006 , 01:54 AM
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im using a different renderer then Maya. Im using Indigo!


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# 109 21-05-2006 , 02:03 AM
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next dumb question what is it, how much is it, is it worth me looking at it or at my level, stick to maya


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# 110 21-05-2006 , 02:14 AM
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its free. its not worth you looking at it unless you can get models to 3ds max and exported to Indigo.

Soon, they will come out with a Maya exporter though (I can't wait!)

this is rendered for 5 hrs in indigo- 2300 mutations per pixel, the model was 20,000 triangles.

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# 111 21-05-2006 , 02:20 AM
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looks truly beautiful. next tin head questions; what are the importance of the triangles, what are they and why is the count so important

next; what are, 'mutations'?

can you bare these questions.


take it easy and life will be easy
# 112 21-05-2006 , 02:23 AM
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Mirek, he did answer those earlier in this thread, lol(if im not mistaken) so take a look around this thread for the answers, lol

sorry if i sound Jerk-ish, lol
cheersuser added image
andy


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# 113 21-05-2006 , 02:24 AM
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yea, you get that on the big jobs LOL, i'll check it out...


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# 114 21-05-2006 , 02:37 AM
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heheuser added image


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# 115 21-05-2006 , 02:49 AM
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Originally posted by MattTheMan
Bidirectional MLT, 400 mutations per pixel, 25 minutes.

thats crazy! i am using 0.4 on a test scene, but i am only get 666.864375 mutations per pixel, in 25 mins!! my comp sux user added image


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Last edited by Joopson; 21-05-2006 at 02:53 AM.
# 116 21-05-2006 , 09:56 AM
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Okay, Matt!
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# 117 21-05-2006 , 12:52 PM
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Joopson: well, my Beveled Cube has 1500 triangles user added image
But Bi-Dir, though it gets less Mutations per Pixel, it gets a better quality overall. The algorithm itslef is slower, but the results are much better and way more accurate then Path Tracing.

If you try Bidir on a bunch of the 0.4 scenes, with 0.4, you will get screwed up results. 0.5 has fixed bidir.

Mirek: Mutations are those changes to the path that are used to explore areas. And the triangles: all graphics geometry is made of triangles. Though people may say quads, for rendering, everything is tesselated to triangles.
Now, the more triangles there are, the more intersection tests must be performed per ray. Indigo has a great Space Partitioning Algorithm, namely, a KD-Tree. Mental Ray has the same thing. This algorithm reduces the amount of tests per ray, but still, the more triangles, the more tests per ray, the longer it takes.


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# 118 21-05-2006 , 01:36 PM
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hey matt, don't get me wrong please,

but you are 13 right, how on earth can you spend your time on rendering triangles and boxes, are you doing kid's stuff as well?
I am not trying to tell you what to do with your life, but your thread really scared me. How many hours you guys spend on browsing forums and tweaking photon settings only for this thread alone seemed crazy to me.

again no hard feelings please, it is just that I don't quite understand the motivation behind all this

# 119 21-05-2006 , 02:20 PM
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lol, of course, I go out with friends at least twice a week, I just set these settings in the morning and leave it running all day.

I play football (american) 3 hours a day, every day (football practice), baseball with some friends once a week... etc.

I also skateboard with friends (if we can get the time to go to a skatepark, which is about twice a month) about every other saturday.

So, I assure you, that 3d doesnt take up much of my life. I have to keep up a "cool" reputation, or else, I will become a total nerdo (at 13, thats bad + i'll lose my girlfriend user added image), and I'm fighting it every day user added image

Oh- and tweaking photon settings alone- with Indigo, you dont tweak anything. You make a light- set it as "SUN", set the cloudyness of the day, and then you run Indigo.

Indigo automatically calculates the strength and color of the light internally. That's why I am using Indigo over Mental Ray for my interior. No need for secondary fill lights, etc... all you do is make a "SUN", set the cloudyness, and render.


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Last edited by MattTheMan; 21-05-2006 at 03:50 PM.
# 120 21-05-2006 , 05:20 PM
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sounds like a healthy way to handle computers, sorry it just seemed like a lot to me when I looked at the thread.
One big advantage of indigo seems to be that it doesn't have a girl's, maybe I should switch so my girl stops making comments about my 2nd girlfriend "maya" user added image

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