H. E. Day <Pov### [at] aolcom> wrote:
: Does anyone know
: of a program that does post processing motion blur without having to render
: 5 or 10 times the number of frames?

  It's not possible to calculate post-process motion blur.

  Well, ok, you can calculate _something_, but it's extremely limited:

  - Only motion blur of an object moving exactly parallel to the viewing
    plane and facing exactly the camera all the time. No motion blur of
    an object moving also in the depth-axis nor changing position with
    respect to the camera, nor rotating, nor changing shape, nor changing
    other features (like color, brightness)... Just think about a rolling
    pool ball...

  - Post-processing can't use sub-pixel information and thus the result will
    be more coarse (it's the same difference as the antialiasing made by
    povray, which calculates sub-pixel information by sending more rays per
    pixel, compared to just blurring the non-antialiased image afterwards
    with a painting program).

  - If some other object reflects or refracts this moving object, the
    reflection/refraction of the object will not be motion-blurred.
    If the object is behind a transparent object, it can't be blurred
    correctly. Specially if the moving object is partially behind a
    transparent object, the blurring will be horribly wrong.

  - If the moving object is partially transparent, the scene seen through the
    transparent part will be wrongly blurred (shouldn't be blurred at all
    if the scene is static). Also if the object is reflecting, the reflection
    will be wrongly blurred.

:  I don't want to used the motion_blur
: {} megapov thing 'cause it's way too slow.

  The motion blur in megapov is suprisingly fast.
  Ok, if your moving object is very complicated and takes a lot of time
to trace even without motion blur and it takes a lot of image area, then
the motion blur makes it slower, of course. However, it will still be faster
than calculating n frames and averaging them.
  For simple objects which render fast, the motion blur in megapov is just
excellent.
  The syntax of the motion blur of megapov makes it also very easy to
calculate the exact amount of blurring per frame (ie. it simulates the time
the shutter is open). By other methods you would have to calculate the
amount of blurring by hand. This can be pretty hard if the motion of the
object is not constant.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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