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So I know that I'm basically asking to identify the main problem to be solved in creating realistic 3d Graphics, but as someone without much technical experience in the field, I'm curious that if these problems can be identified, what the issue is with implementing them programmatically.

The picture below from Hitman is what I would call "ultra-realistic". But, it still definitely looks like a 3d model. If you were to put a photograph of the same scene with a real actor and background, there would probably be some differences obvious enough to be able to point out which is which.

Why is that? < 100% accurate subsurface scattering? Is the lighting ever-so-slightly off? etc.

enter image description here

PS, sorry for tag choices. I am not familiar enough with this SE to know what to choose. Please edit better ones in, if you know any.

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    $\begingroup$ This is actually a very interesting question. I really hope this isn't considered off topic here. $\endgroup$ – ivokabel Jun 3 '16 at 8:25
  • $\begingroup$ An oft-overlooked feature is how well (or poorly) the scene data was mapped to the display. It's common for high-dynamic-range scene data to be arbitrarily "squashed" into an sRGB range without careful mapping. This can create a lot of VERY subtle problems that cue the brain to be skeptical. A great (generic) discussion was started here: blender.stackexchange.com/questions/46825/… $\endgroup$ – mHurley Jun 6 '16 at 19:59
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Few things, but usually this is what it takes to make the difference:

1- the material reflection at his head, he is bald, yet the diffuse texture shows color difference where the hair is, this means he has a shaved head, not a natural bald, this should translate in reflection, take a look at his head, top right (top left for the image), the reflection is very smooth, no bumps at all, there should be some indication in reflection to the tiny hairs that you can see in the texture map.

2- the wrinkles in his face need to be emphasized, he looks like some kind of a worrier, yet he has very smooth skin like a 15 year old has, I'm not talking about deep scars, I am talking about skin texture and bumpiness due to rough way of life, skin bumps, moles, a minor infection that will affect both coloration and bumpiness.

3- his mouth is off, the size and positioning, I know that many people has small mouths, and a relatively large distance between the nose and the mouth, but that drives the attention of the viewers, it feels wrong, even if it was a photo of a real person, you can spare this kind of dragging attention to extreme shapes if reality is what you're after.

4- This is a minor thing, but it had a role to play, the background and outfit, they look fake, this drives the viewers automatically and subconsciously to feel that this is not real, try to put more effort in these, making the outfit less uniform, and the background to have more realistic pattern, with more hue variation.

5- And last, the eyes, there's no reflection, yet the lighting is low and the image is small, so I am not sure if this is due to lighting or to the material itself.

That all been said, all these remarks are minor, the artwork looks awesome, I don't think a CG artwork should look like a photo, a perfectly realistic CG artwork that looks exactly like a photo, will become just another photo to the viewer.

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  • $\begingroup$ As to your last comment - it's not a requirement of course for CG to look like a photo, but the goal of a lot of animation is to look as life-like as possible. Maybe I picked a less-than-perfect example, but I've always been interested in how real-time rendering could be made more realistic, especially in games. $\endgroup$ – galois Jun 7 '16 at 18:29
  • $\begingroup$ Of course, in this case I was talking about the information provided in the question, so I was discussing a still image. For extra realistic look, I don't know what software you're using, but if it's Blender, there's a new LUT that can be replaced (not official yet) which makes Cycles rendering very close to real life filming quality, concerning material's reaction to light, lighting is a major aspect, specially when discussing photo real. $\endgroup$ – a25bedc5-3d09-41b8-82fb-ea6c353d75ae Jun 7 '16 at 18:36
  • $\begingroup$ So do you think it's often the case that while something is almost realistic, the CG is "designed" (if you will) with the idea that it shouldn't be picture-perfect? $\endgroup$ – galois Jun 7 '16 at 21:09
  • $\begingroup$ I wouldn't use "Should not" or "must not" with anything related to an artistic matter, there is no should nor must in art, everything is subjective, what I meant is that (as I believe) a glance of non realism, even in realistic artworks, keeps a small window open to the personality of the artist, compared to stylized artworks which for this example would be no roof at all. It all depends on were you like to stand. $\endgroup$ – a25bedc5-3d09-41b8-82fb-ea6c353d75ae Jun 7 '16 at 21:43
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Hard to say because we can not see the code. Subsurface scattering might be part of that equation.

I would just point out that human brains are extremely specialized in facial recognition. It has been postulated that the brain has a inbuilt defence mechanism to detect alien impostors/anomalous people. You are right in middle of what is known as uncanny valley nothing sort of near perfect seems to get it right, it seems

It is also worth noting that we do not really know what it is that is lacking that puts you in uncanny valley. So it seems to me we do not conclusively know what, if anything, is missing. So the entire thing might be because we are neglecting something important but as of yet unknown.

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I think you identified the problem yourself in your question :

it still definitely looks like a 3d model

It's obviously hard to tell and subjective, but while many things are off in this picture, the expression and the proportions of the character model are what I find most unrealistic. It is to the appreciation of the art director, but most of the time, realism is not the main drive in shaping and animating character models. Here we have all the clichés of bland character design, and a significant lack of effort put in the expressiveness of the character. It feels 100% designed as a game persona. As such, no matter how close to reality all visual phenomenons are transcribed, my brain just won't accept it, as no-one looks like that in real life.

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    $\begingroup$ The things that stand out to me about the model are its symmetrical features. Not all of these are mismatched on all people, but most people have some asymmetry. This model has ears positioned at the same height. The wrinkles in general are symmetrical, particularly the frown lines on the left and right of the bridge of the nose. In addition to these permanent features, the expression is also very symmetrical. None of these things are impossible on a human face, but they invite closer inspection, making it more difficult to miss other subtle clues that the face is artificial. $\endgroup$ – trichoplax Jun 4 '16 at 0:38
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    $\begingroup$ The reason why i would not want to go there is that i know that the fact that it IS artificial makes you more sceptical and start to see things that may or may not be critical. Yes i agree its a archetypical character. But again since its not a blind test i would refrain from few of the points. $\endgroup$ – joojaa Jun 4 '16 at 6:00
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I see several things that are off in addition to what others have said. He doesn't appear to be breathing. He's in a very cold place (it appears to be snowing), yet there's no breath in front of his nose or mouth. It's snowing, but none of the snow is in front of him. It's all behind him, or on his clothes, but not falling around him.

I feel like our brains pick up on the subtler things, too. Like the fact that his eyebrows are just a flat texture mapped onto the geometry of his face. They're not separate hairs. Even though you couldn't resolve them very well at this distance, I think we still notice it a little. There are no specular highlights on them, either.

And to me his skin looks rubbery, not alive. I know that in the cold my skin gets a little blotchy - some parts get more pinkish than others. His coloring is very even.

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