Comment by hughes | Hacker News Reader

Comment by hughes | Hacker News Reader

Parent Full thread

We have gotten very good at nearly perfectly rendering images that accurately capture the behavior of light and materials, but I feel like to produce truly convincing CGI we need to improve the imperfections that we have come to expect from more traditional media.

As other commenters pointed out here, the opening nature valley scene was unconvincing. I think this is partly due to the author not having modeled the limitations that affect physically filming a similar scene.

- a helicopter or airplane could not plausibly move along the track shown in the opening shot

- camera rigs have imperfect tracking control, sometimes biased along certain axes

- high res 4k sensors have physical limits and defects. the scene is rendered as if captured by a totally perfect sensor

Simulating the motion of a helicopter that doesn't even appear in the shot seems well beyond the effort that most digital artists are willing to go to, but I think these sort of things are key to producing something truly convincing.

That's the point. The opening scene is the uncanny valley and supposed to be not quite realistic

That was my read as well. He even intentionally dropped the frame rate.

In addition to that list, there are the physical issues of film and optical devices. CGI can just work around them, but with film and lenses, physics still gets yah. For reference (http://www.quadibloc.com/science/opt0505.htm) the first order optical issues with all systems are:

> Spherical Aberration: this is the aberration affecting rays from a point on the optical axis; because rays from this point going out in different directions pass through different parts of the lens, then, if the lens is spherical, or otherwise not the exact shape needed to bring them all to a focus, then these rays will not all be focused at the same point on the other side of the lens. Essentially, lenses are spherical, they need to be parabolic but that is very expensive.

> Coma: this aberration affects rays from points off the optical axis. If spherical aberration is eliminated, different parts of the lens bring rays from the axis to the same focus. But the place where the image of an off-axis point is formed may still change when different parts of the lens are considered. Essentially, your lens may not be flat compared to the film.

> Astigmatism: this is another aberration affecting rays from a point off the optical axis. These rays, as they head through the lens to the point in the image where they will be focused, pass through a lens that is, from their perspective, tilted. Even if neither spherical aberration nor coma prevents them from coming to a sharp focus, if we consider the rays of light that are in the plane of the tilt, and the rays of light that are in the plane perpendicular to that, these rays pass through a part of the lens with a different profile. So they may not be focused at the same distance from the lens, even if they do come to a focus in each case. Essentially, lenses aren't perfectly spherical and may have a more cylindrical portion.

> Curvature of Field: even when light from every point in the object is brought to a sharp focus, the points at which they are brought into focus might lie on a curved surface instead of a flat plane. Essentially, lenses are round, and film is flat.

> Chromatic aberration: Essentially, red light focuses at a different distance than blue. This is the reason for rainbows.

Reply on news.ycombinator.com