Re: Scanline Smear...

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Rémi Arnaud (remi++at++remi.engr.sgi.com)
Thu, 19 Mar 1998 10:43:37 -0800 (PST)

Steve Baker wrote:
>
> On Wed, 18 Mar 1998, Jan Barglowski wrote:
>
> > Performers:
> >
> > I have a task to create scanline smear, that is, imagine a video camera
> > panning so quickly that by the time the bottom scanline is imaged, the
> > camera's heading is not close to when the top scanline was imaged. I
> > am not interested in the scanline compression/expansion that also may
> > happen, just the effect between scanlines.
> >
> > Solutions I've thought of:
> > - create a channel for each scanline and run the app at 240X (yikes!)
> > - create a slightly larger image, then shift the pixels manually with
> > glReadPixels() et.al.
> > - create a slightly larger image, and texture map it to a quad and
> > stretch the quad along diagonally opposite corners in proportion to
> > the speed of the pan.
>
> On iR, the last one will work faster than any of the others. Whether you
> make 60Hz depends on a lot of factors. Also, don't deform the quad, just
> change the texture coordinates at its vertices.
>
> > Has anyone done something like this before?
>
> Not for shearing the image - but I do use it to zoom an image (to make
> it deliberately 'pixellated'.
  An other way to pixellize or defocus the picture is to force the texture filter
  to use a coarser resolution, and force DVR.

>
> In my case, it was a very small monochrome image - but some of the
> SGI demo's I've seen use this technique for non-linear image
> pre-distortion for dome displays and such. At least one of those
> demos ran at 60Hz IIRC (although the resolution was not really huge).
>
> Steve Baker 817-619-8776 (Vox/Vox-Mail)
> Raytheon Systems Inc. 817-619-4028 (Fax)
> 2200 Arlington Downs Road SBaker++at++link.com (eMail)
> Arlington, Texas. TX 76005-6171 SJBaker1++at++airmail.net (Personal eMail)
> http://www.hti.com http://web2.airmail.net/sjbaker1 (personal)
>
> ** Beware of Geeks bearing GIF's. **
>
>
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