I forgot to say: In my experience with virtual motion blur, blurring the entire
duration of the frame gave the smoothest and most continuous sense of movement.
Which isn't terribly surprising. Our game was running at 60 fps and we did 3
blur samples, creating the impression of a game at 180 fps downsampled to 60,
this really felt smooth. Though the lower the frame rate gets the more obvious
the blur becomes and the less it feels like movement.

Personally I'm not a fan of the 24fps standard of movies for exactly that
reason, in busy action scenes you can really lose any sense of how things are
moving. Of course good directors use that confusion to good effect, like the
Bourne films and the aforementioned Private Ryan sequence.

And regarding the shutter time, I'd probably write the code like this:

#declare NumSubFrames = 10;
#declare ShutterProportion = .5;
#declare ActualFrame = int(frame_number/NumSubframes);
#declare SubFrame = mod(frame_number,NumSubframes);
#declare Time = (ActualFrame + SubFrame*ShutterProportion)/FramesPerSecond;


"Kenneth" <kdw### [at] earthlinknet> wrote:
> "Tek" <tek### [at] evilsuperbraincom> wrote:
>
> > Interesting. I've played with similar things on a realtime motion blur effect a
> > few years ago. I assumed the shutter time could be adjusted (to control exposure
> > as well as motion blur, much like the aperture does for focal blur) but I never
> > actually researched what real cameras do. Is it always 50%?
>
> In a general sense, yes. (Although, as you say, cinematographers are always
> fiddling with shorter exposure times, for effect--that is, an open shutter
> *less* than 180-degrees. Pro film cameras have this variable feature. The D-Day
> landing sequences in SAVING PRIVATE RYAN would be a good example of such an
> effect; the image frames seem to be almost devoid of motion-blur, kind of a
> jittery strobe-like quality.) At the other extreme, I think there are some pro
> cameras that may have as much as a 220-degree open shutter--certain
> models of Panavision or Arriflex, possibly. My guess is that they are more
> useful in low-light situations. Or simply to impart *more* blur per frame, for
> whatever artistic reason.
> >
> > The thought occurs that you might get a more film-like effect if your first
> > and last sub-frames had a gradient to black on them, to simulate the blur of
> > the closing shutter! But I'm probably over-thinking this.
>
> I was thinking about that too! Wondering (in a theoretical sense only!) how to
> reproduce it. You're idea sounds like it might just work.
>
> BTW, the 'skip-action' code that I posted seems kind of sloppy, now that I look
> at it again. :-(  I should have cleaned it up a bit.
>
> Ken

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