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Comment by pdelbarba | Hacker News Reader

I think it depends on context. There are a lot of sim games where the environment is very controlled and forums are littered with people who can't tell whether the occasional picture is real or in-game. A forest is hard to render accurately but a plane in flight is pretty trivial

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Forests have pretty much been solved. Look at games like Shadow of the Tomb Raider, forest looks amazing. The difficulty now is limited to finer details, like hair. Hair is still pretty much unsolved.

See? It’s almost deterministic. People really can’t accept that we don’t know how to do something.

Plop a nature video next to your forest rendering and it’ll become apparent just how unsolved trees are. And everything else, for that matter.

The precise claim is this: viewers should be able to identify a rendered video no better than random chance. If you conduct this experiment, you’ll see that real videos from actual video cameras wipe the floor.

> If you conduct this experiment, you’ll see that real videos from actual video cameras wipe the floor.

To be fair: have you run such an experiment yourself, or are you just assuming that this conclusion will always result?

The motion blur will probably give it away. Accurate video motion blur is computationally expensive but conceptually simple. Just render at about 100 times your target frame rate and average batches of frames together in linear colorspace. You can speed this up by rendering at a lower frame rate (e.g. 10 times your target frame rate), estimating motion, and blurring along the motion vectors before averaging the frames. You can further speed it up by using an adaptive frame rate depending on motion speed and contrast. But a lot of rendered video doesn't even try. Look at a fast-moving bright point of light and you'll easily see the difference.

(But note this is only replicating video, not reality. Truly realistic motion blur requires ultra-high displayed frame rates beyond the capabilities of current hardware.)

A lot of games fake the motion blur so badly. Racing games are often especially guilty.

If you're driving at 200 mph, and there's a car next to you also going 200 mph, it shouldn't be blurry.

Also, the length of the blur should not exceed the distance an object travels on your screen in 1 frame. In other words, if an object moves 30 pixels from one frame to the next, then the blurred image shouldn't be more than 30 pixels wide.

This feel like multiple logical fallacies. It seems funny to me to claim in advance that people are going to argue with something that was intentionally non-specific, vague, controversial, unproven, and at least partly wrong, and then when someone argues with you, claim you were proven right. It's easy to predict that someone will argue with something misleading or wrong, and that doesn't give your CG argument any credibility.

What CG videos are you considering, what specifically have you looked at? Can you show some good faith examples of the best CG forests ever made, compared to some specific nature videos? Are you talking about attempts to match a nature video, and saying it's not possible regardless of what's in the shot?

Are you looking at the best examples of CG forests lately? There are some CG full frame video examples of forests I don't believe people would reliably identify as CG, if they didn't know before hand and you left out the explosions & spaceships.

https://www.youtube.com/watch?v=xOpuDhWzV1I

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