Darren New <dne### [at] sanrrcom> wrote:
>
> Couldn't you have the original being 110 frames long, then, blended down to
> 100 frames?

The motion blur is meant to be the movement that occured whilst the camera
shutter was open for that frame, so it needs to uses images from periods of time
in-between frames, not overlapping with other ones. So the first frame needs
multiple samples of the motion that occured in the first 1/30th of a second, the
second needs the next 1/30th of a second. I chose to take 10 samples of the
movement over the course of a frame, hence I need to render 10 times more
frames.

If I overlap it I get a 1980's video ghosting-trails special effect, not motion
blur :)

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Tek wrote:
> If I overlap it I get a 1980's video ghosting-trails special effect, not motion
> blur :)

Makes sense. :-)

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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Darren New <dne### [at] sanrrcom> wrote:
> Tek wrote:
> > If I overlap it I get a 1980's video ghosting-trails special effect, not motion
> > blur :)
>
> Makes sense. :-)
>
> --
> Darren New, San Diego CA, USA (PST)
>    Serving Suggestion:
>      "Don't serve this any more. It's awful."

Ah what the hell, it's fun to try it anyway! Here's a version that takes 100
original frames down to 90. Instead of each frame representing just the 1/30th
of a second for which we see the frame, it is instead showing 10*1/30th = 1/3rd
of a second's worth of motion blurred together!

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Attachments:
Download 'anim_test_100to90.avi.dat' (788 KB)

On 12/11/2010 5:47 PM, Tek wrote:
> Ah what the hell, it's fun to try it anyway!

The 80's Rulz :-D

-- 

Best Regards,
	Stephen

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"Tek" <tek### [at] evilsuperbraincom> wrote:
> Darren New <dne### [at] sanrrcom> wrote:
> >
> > Couldn't you have the original being 110 frames long, then, blended down to
> > 100 frames?
>
> The motion blur is meant to be the movement that occured whilst the camera
> shutter was open for that frame, so it needs to uses images from periods of
> time in-between frames, not overlapping with other ones. So the first frame
> needs multiple samples of the motion that occured in the first 1/30th of a
> second, the second needs the next 1/30th of a second. I chose to take 10
> samples of the movement over the course of a frame, hence I need to render
> 10 times more frames.

I generally use 10-frame 'batches' as well--seems to be a good compromise
between motion-blur quality and rendering time (creating all those static
images.)

Lately, I've been experimenting with a subtle alteration of how those initial
frames are generated, to try and get more of a 'motion-picture camera' look to
the blur: Since a real camera usually has what's called a 180-degree shutter
(where any film frame sees only 'half' the blurred action--1/60 sec. in your
example, though I use 1/48-- then the shutter blocks the other half while the
film is being transported), I've duplicated that by altering POV's clock value
(plus other stuff). Here's the code I use:

#declare SF = 10; // the number of animation frames to render for each
// averaged batch.
#declare I = frame_number;
#declare D = I*(1/SF); // If the averaged batch size is 10, this counts up in
// 10th's of a frame_number; at frame 10, D = 1; at frame 20, D = 2, etc.
#declare jumper = ceil(D)*SF*clock_delta - SF*clock_delta;
#declare CK = jumper + clock_delta*frame_number; // the new CLOCK (substitute
// it everywhere clock is used in scene). BTW, clock_delta*frame_number is
// probably just clock.

And in my INI file, Initial_Clock is set to 0, and Final_Clock will always need
to be 1/2 of whatever it would normally be.

So every 10 frames, the value of CK jumps ahead, which causes all the
clock-based equations to skip the next 10 frames worth of action. No useless
'black' frames are generated, and the resulting frames can be averaged as usual.

But does it 'look' more realistic? Hmm, probably a matter of taste.

Ken

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"Kenneth" <kdw### [at] earthlinknet> wrote:
>
> Lately, I've been experimenting with a subtle alteration of how those initial
> frames are generated, to try and get more of a 'motion-picture camera' look to
> the blur: Since a real camera usually has what's called a 180-degree shutter
> (where any film frame sees only 'half' the blurred action--1/60 sec. in your
> example, though I use 1/48-- then the shutter blocks the other half while the
> film is being transported)

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%?

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.

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"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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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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"Tek" <tek### [at] evilsuperbraincom> wrote:
>
> #declare NumSubFrames = 10;
> #declare ShutterProportion = .5;
> #declare ActualFrame = int(frame_number/NumSubframes);
> #declare SubFrame = mod(frame_number,NumSubframes);
> #declare Time = (ActualFrame + SubFrame*ShutterProportion)/FramesPerSecond;

Typo! That should have been in a [0,1) range like so:

#declare SubFrame = mod(frame_number,NumSubframes)/NumSubframes;

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"Tek" <tek### [at] evilsuperbraincom> wrote:

> 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;
>
> Typo! That should have been in a [0,1) range like so:
>
> #declare SubFrame = mod(frame_number,NumSubframes)/NumSubframes;

Sorry for the delay in responding; wanted to thank you for this re-worked code.
Haven't used it as yet, but it certainly looks more elegant than mine! I rarely
(if ever?) use mod; I need to add that to my 'permanent mental toolbox' of
POV-Ray tricks.

Ken

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