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Motion blur in games

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I'm sure by now we have all had a good look at the motion blur used in crysis. I am just interested to see the opinion of my fellow developers on this. Here is what i think. Personally i think the motion blur used in crysis looks for the most part terrible and feels very unrealistic. I mean go stand out side and do a quick 90 degree turn, do u see motion blur? hardly. When u r moving at fast rates such as when you are in a car, sure a large degree of motion blur will take place. It certainly does not happen every time you are walking and you make a slight turn like in crysis. It can be a great effect if used properly but i think crytek have gone way overboard with it. Hopefully they tone it down in the full release.

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Oh, I beg to differ. Having had played through the single player demo, I did not feel that it was overdone at all. Motion blur in human vision is far more prevalent that you think; it's just that you don't notice it as much. Motion blur plays a very important part in supressing temporal artifacting. It's one of the reasons why camera footage appears very smooth even at framerates as low as 24fps, while games must maintain framerates of about 60fps to remain smooth.

I noticed this smoothing effect in both HL2:EP2 and Crysis. After playing Crysis, I could have sworn that my framerate never dipped below 40fps... but my framerate counter told me I was running at about 25fps. I think many will agree that Crysis "feels" much smoother than many other FPS games, even though it usually maintains lower overall framerates.

Also, I think you must remember that many post processing effects such as HDR and motion blur don't try and capture what the eye sees, but rather what a camera sees. In real life, the human eye doesn't adjust exposures in a matter of seconds, nor does it see lens flares or exorbitant blooming.

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The human eye does have a degree of bloom, but lens flares in games really annoy the hell out of me. That screams "wannabe film-maker" in my opinion.

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So how is the effect that you are talking about done, does it effect the everything at once (walls, floors, people)?
For example my own application has just 1 mesh that duplicates it's self and alpha fades for a trail effect. It's of course not very good and I'm considering other possibilities.

It sounds like you are saying this motion blur looks about the same regardless of frame rate, how?

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As I understand it, they use a "real" motion blur technique - each pixel gets a velocity and points are sampled along that vector. The method you describe is a quick and fast way to achieve motion blur, but only works well when changes each frame are slow. It breaks down when objects or the camera are moving very fast.

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Quote:
Original post by Sc4Freak
Also, I think you must remember that many post processing effects such as HDR and motion blur don't try and capture what the eye sees, but rather what a camera sees. In real life, the human eye doesn't adjust exposures in a matter of seconds, nor does it see lens flares or exorbitant blooming.

I agree and disagree with this at the same time...
Lots of games try to reproduce what a camera sees - but frankly, in a first-person perspective game it makes no sense to be seeing through a camera!
These effects *can* also be used to simulate what an eye sees.

HDR can be used to simulate a human eye as well as a mechanical camera - but for some reason most games seem to try and reproduce the mechanics of a camera, not an eye. The slow rate of change in exposure, or the constant oscillation that occurs in same games really breaks the immersion for me - it's like the developers are shouting out "Hey look, we have HDR!!!" instead of just using it for it's intended purpose - to simulate the display of a greater range of colours than the monitor actually supports.

Bloom is a neat illusion that fools the eye into thinking a pixel is brighter than it really is (by bleeding lighting into surrounding pixels) - bloom is an important technique for creating realistic looking scenes on a regular monitor with a limited range of brightnesses. If we had HDR monitors, you shouldn't really need bloom anymore, as the monitor could make each pixel insanely bright causing the eye to see the 'bloom effect' naturally.

Motion blur can be useful for covering up low frame-rates, but unless it is very subtle (or only happens at high speeds), it's not very realistic. However, if you're viewing a fast-moving scene (at decent frame-rates) then your eye is already going to blur it naturally, so you're doubling up by simulating it in your renderer.

As for lens-flares - don't do these unless you're looking out of a camera! I remember one FPS I played where lens-flares were only visible when looking though a scope - this was a very sensible use of the effect!

Blur may have more uses in the distant-future though: your eyes are constantly (sub-consciously) rotating at about 1º per minute or less, causing a subtle motion blur which your brain uses to help determine the depth of objects - if we could find a way to simulate this blurring in the renderer, we could fool the brain into perceiving depth in the flat screen! You would have to be able to accurately measure the position/rotation of the viewers eyes to do this though...

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^ Motion blur in racing games (some racing games) seems realistic to me. It definitely makes the scene more convincing.

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Temporal aliasing is an evil thing! At times it can be worse than pixel aliasing for breaking the realism of a scene. Of course screen-space motion blur is hardly a solution to the problem, but if done correctly it can do a a good job of masking the aliasing. Temporal super-sampling is the ultimate solution, but its about as feasible as super-sampling for pixels.

In the case of Crysis, the game is attempting to model a camera and therefore its motion blur is based on a shutter speed (which you can modify through the console, if you choose). If you were to take a video camera running at 24fps and move it 90 degrees very quickly, I can guarantee you there will be excessive blurring!

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