It's not meaningless at all, it's a close approximation of light absorption that happens to be measurably and perceptually indistinguishable from the physical spectral absorption process, save for a few corner cases that are being worked on.
It's amusing that you brush it off with "Oh, there are a few corner cases." Those corner cases are why it doesn't look real.
And no, it's not 99.9% accurate. You may be thinking of constrained scenes, where e.g. you shine a laser on a substance of a specific color and then measure the resultant color combination. But the complexity of real life defies such analysis.
If you're going to say I've missed some recent work, you'll need to cite sources. Then we can debate those.
EDIT: To clarify:
Your argument is attacking the non-simulation aspects of rendering without addressing whether a simulation that is simpler than real life is acceptable. If I can't tell the difference, does it count?
My argument is that if you get a bunch of people together, show them simulated video and real video, and ask "Which of these are simulated?" they will correctly identify the simulated video as "not real" with significant accuracy -- given modern techniques, probably >95% accuracy. The simulation needs to be of a non-trivial scene, like a waterfall or a valley. When you show real video side-by-side with simulated techniques, there's no contest.
If we truly knew how to make simulated video that looks real, without mixing any real-life footage, then the observers in the above scenario wouldn't be able to do any better than random chance. But they can, because we can't.
I did cite a source: subsurface scattering is an example of simulating light absorption. It is an example of things that you just claimed aren't getting better actually getting better.
You're attacking my arguments and getting more hyperbolic without any examples. What specifically doesn't look real? What are you actually claiming? What is your criteria for whether something is "real"? What corner cases are you thinking of that cause color multiplication to break down so frequently that it's a bad approximation most of the time? Can you give some examples of state of the art CG that intended to improve realism but doesn't look real?
I'm not claiming that everything looks real, nor that all CG is realistic. I'm claiming that CG is getter better over time, and that some things are already indistinguishable from real. The number of CG things that look realistic is going up over time, and it used to be 0. There is a trend here that reality contradicts your original basic thesis that nobody can rendering something realistic.
My 99.9% number wasn't a claim, it was a made up number (which I thought was obvious, sorry). I said "If the result is 99.9% accurate... then it's a valid model" to back a point: the point is that if multiplication is predictive then it's a valid model. That's how all of physics works. Acceleration under gravity is an approximation.
You haven't demonstrated that multiplying doesn't work, you've only stated an opinion. I'd like to see some examples of what you mean, because it appears to work very well from where I'm sitting. The colors of grass, bricks, wood -- diffuse materials -- is very closely approximated by multiplication, enough that we can in fact measure how good the approximation is, and humans cannot tell the difference. Therein lies the problem with your argument -- if I can't tell the difference, that is my definition of realistic. It doesn't matter what happened under the hood. You seem to be claiming that only reality is good enough to be realistic, because anything else is cutting corners.
I'm not sure I understand what you mean about real life defying BRDF measurement. One of the ways that CG is getting more realistic is precisely through various gonioreflectometers, some of which shine lasers and measure the output from all angles. Material catalogs are currently being constructed and sold to CG companies using higher and higher resolution measurements of exactly what you're claiming isn't possible and doesn't help. People buy them because they improve realism.
> My argument is that if you get a bunch of people together, show them simulated video and real video, and ask "Which of these are simulated?" they will correctly identify the simulated video as "not real" with significant accuracy -- given modern techniques, probably >95% accuracy.
Every year Autodesk runs the test "Fake or Foto". http://area.autodesk.com/fakeorfoto Less than 10% of people are getting them all right this year, and a considerable number of people are under the 50% line. This isn't scientific, of course, but see if you can score 100%. This is an indicator that CG is pretty good. Will you admit it if you don't score 100%?
Earlier you made an argument that stills are looking okay, but moving things aren't. The problem with that argument vs color multiplication is that color multiplication is used on stills, so if that's what's breaking down, stills should be obviously unrealistic.
It's very difficult to figure out what the core of your argument is. We can't create simulated video indistinguishable from real life, and I've given you an experiment that will prove that we can't.
You haven't demonstrated that multiplying doesn't work, you've only stated an opinion. I'd like to see some examples of what you mean, because it appears to work very well from where I'm sitting.
It's not an opinion that multiplying colors has nothing to do with how light behaves in real life. I even said that it was an approximation that works fairly well, so if you're going to simply ignore the things that I did say, this discussion isn't going anywhere productive. The point is that it's an approximation, and it's partly why we subconsciously recognize simulated video as fake.
Every year Autodesk runs the test "Fake or Foto"
Obviously, photos don't work. It doesn't pass the realism test. This conversation is about video -- the human visual system processes video completely differently. It's not just a matter of taking still frames and stringing them together. The test is invalid. If you use video (of non-trivial length, with non-trivial scene complexity -- any nature video will do fine), you'll see the participants' accuracy skyrocket to nearly 100% correctly identifying simulated video.
If you're truly curious about the reasons why a simulated video looks fake, look into some books about the neuroscience of visual processing and color perception. One of the fundamental tenets is that colors affect colors around them. To make something that looks real, you need to get the colors exactly right. Even a small departure from reality will ruin the entire effect. That's partly why multiplying colors is problematic, since it results in a departure from real life behavior. The other half of this is to ignore any test involving still frames. We don't perceive still frames the same way as video -- it's why video compression is different, for example -- so we can't use stills in any test of realism.
Whenever someone points out that we really don't have a clue how to make simulated video indistinguishable from real life, someone comes out of the woodwork to point out all the reasons why it's right around the corner. That's been false for a decade, and it's not looking any better for the upcoming decade. It's easy to prove me wrong: Get a bunch of simulated videos together and show them to observers, mixed with real videos. They'll spot the real videos every time, if you don't use constrained or simplified scenes. Nature videos work well.
It seems like people just don't like the idea that graphics programming is a bag of tricks. They want it to be deeper. But you can throw in all the physically-based techniques you want, and the resulting video still won't look real.
I have to go to an appointment now, but maybe we can continue this in a few hours if you want.
> It's very difficult to figure out what the core of your argument is. This conversation is about video ...
Ah, I see the problem. You're right. I thought I was debating the idea that "nobody knows how to make anything look real.. no one knows." I just checked, and your first post didn't say anything about video. Your second one mentioned it in passing, but I didn't realize it was a constraint on what I could talk about. I see why I'm confused, and why I'm confusing you. I'm sorry! Honestly. I am indeed thinking of some other things besides 100% fully simulated video of nature that is unconstrained, when I try to make the claim that some people do know how to render some things realistically.
Here's a pretty good CG video, in my opinion. Which parts look fake to you at a glance? http://vimeo.com/15630517
> You appear to be offended by the idea that we can't create simulated video indistinguishable from real life. But we can't, and I've given you an experiment that will prove that we can't.
That's a negative. Personally, I don't think I can't prove a negative, with any experiment. Are you sure it's provable?
Here's the core of my argument, the part that I thought I was debating. I think realism (undetectable to people) has been achieved with: material samples, constrained physics simulations, stills images of architectural scenes, limited still images of natural scenes, elements in video (mixing live and CG footage), fully CG video environments for short periods of time, humans & faces but only in fairly constrained situations for short periods of time. I don't think realistic humans have been achieved in general. I do think realistic simulated video - that meets your criteria - will happen eventually, and I don't know when or claim anything about when.
> Obviously, photos don't work.
But you can demonstrate some color multiplication problems in fake photos, right? You're ruling out still images yet the only problem you've cited is one that affects every single pixel of all still CG images.
> Get a bunch of simulated videos together and show them to observers, mixed with real videos. They'll spot the real videos every time, if you don't use constrained or simplified scenes. Nature videos work well.
Okay, fair enough. I don't know what "constrained or simplified" means. Your goal posts could be anywhere, so I definitely can't win. I don't think this is easy though -- the best CG is very expensive still, making something that looks very realistic is difficult. I could agree here and now that no CG ever rendered yet passes the unconstrained environment and complexity test when it comes to realism, and I would agree that realism is easier to achieve the more constrained and simplified the scene is. My argument is that the threshold for where too complex triggers unrealism is moving in the direction of more complex over time.
> It seems like people just don't like the idea that graphics programming is a bag of tricks. They want it to be deeper. But you can throw in all the physically-based techniques you want, and the resulting video still won't look real.
Now I'm getting really confused. Graphics is a bag of tricks, I don't have a problem with saying that, so I don't know which people you're talking about. Those of us practicing graphics have been saying that all along.
But you're saying that it can never happen? Using all the physically based techniques now existing and ever to be invented, it will never happen? I could simulate reality, and I won't ever get there, no simulation will?
I can see that you've thought about this a lot, and I can see that you know a lot about graphics. I honestly thought you were saying we're not physically based enough yet, and I was trying to show how we're getting there, but now I'm not sure I understand what your claim is, or what we're talking about. I do suspect we're getting down to what my friends call the "dictionary problem" - agreement that is accidentally violent due to miscommunication over a few words.
You can easily blow his claim out of the water by showing a video that is fully computer rendered but looks real.
Parts of the video you offered look very realistic, but the content breaks the sense of realism, e.g., vegetables shattering into tiny pieces, rocks tumbling upwards, etc.
i read this discussion as sillysaurus3 arguing the wrongness of ALL models, while not acknowledging dahart's examples of utility: constrained/simplified for some is good enough for others.
It's amusing that you brush it off with "Oh, there are a few corner cases." Those corner cases are why it doesn't look real.
And no, it's not 99.9% accurate. You may be thinking of constrained scenes, where e.g. you shine a laser on a substance of a specific color and then measure the resultant color combination. But the complexity of real life defies such analysis.
If you're going to say I've missed some recent work, you'll need to cite sources. Then we can debate those.
EDIT: To clarify:
Your argument is attacking the non-simulation aspects of rendering without addressing whether a simulation that is simpler than real life is acceptable. If I can't tell the difference, does it count?
My argument is that if you get a bunch of people together, show them simulated video and real video, and ask "Which of these are simulated?" they will correctly identify the simulated video as "not real" with significant accuracy -- given modern techniques, probably >95% accuracy. The simulation needs to be of a non-trivial scene, like a waterfall or a valley. When you show real video side-by-side with simulated techniques, there's no contest.
If we truly knew how to make simulated video that looks real, without mixing any real-life footage, then the observers in the above scenario wouldn't be able to do any better than random chance. But they can, because we can't.