[mythtv-users] Deinterlacing Methods

James Buckley xanium4332 at googlemail.com
Mon Jan 15 07:48:53 UTC 2007

On 15/01/07, Daniel Kristjansson <danielk at cuymedia.net> wrote:
> On Sun, 2007-01-14 at 21:44 +0100, Wim Fokkens wrote:
> > Hi Daniel
> >
> > > You will never get a perfect picture with a progressive display..
> >
> > I have to disagree with that.
> I'm sorry but that is impossible.
> > And the picture quality is absolutely perfect and easily beats the
> picture
> > quality of my STB connected with RGB scart. I think the main reason for
> this
> > easy win is the fact that my radeon card can do very good deinterlacing
> in
> > hardware. And PowerDVD codec makes good use of this.
> Very good deinterlacing is possible. And with material that was
> originally not interlaced, like movies, you can reconstruct
> the original progressive frame. But no physically constructable
> device can display it perfectly. You would need to flash the
> backlight on for an infinitesimally short time once per frame,
> this would require infinite power. You could get close enough,
> say by projecting a light which flickers on for a few
> milliseconds through film 24 times per second. But LCD's and
> plasma displays are far from this ideal. Plasma phosphors glow
> for milliseconds, and worse the image is updated row by row.
> LCD's backlights blink at something like 40,000 hz they
> effectively give off light constantly. This gives us a nice
> flicker free display for static images but it also means you
> see the row by row update and the image is constant for a long
> time so your eye can not reconstruct it into a moving image as
> smooth as the moving image reconstructed by your mind when you
> see images that flash onto the screen whole for a short period
> of time. You can construct a device which shows progressive
> material better using three DLPs or three LCDs and a shuttered
> HID lamp, but these devices are very expensive; and you need
> to watch them in a darkened room.
> > I also have a MythTV pc with the following specs:
> > I am trying very hard to get the same picture
> > quality as my MyTheater system. But I don't even come close.
> > A can get to the same level as James Buckley did.
> > I also tried XVMC but judging from the picture it is only doing Hardware
> > Motion Compensation but no hardware deinterlacing.
> > Why is this? Is there no support for hardware deinterlacing in the
> Nvidia
> > driver?
> There is some support. The XvMC API allows us to display the
> odd field, even field, or both fields of an image. This is
> enough for us to do either bob or one field deinterlacing.
> But it is not enough for us to something like 3-2 pulldown,
> i.e. perfect reconstruction of material that was originally
> not interlaced. We also can't do anything like Lancos, kernel,
> or linear blend with XvMC. nVidia has another library which
> they call PureVideo, it is much better and is probably what
> is being used in your MyTheater system but it is not available
> on Linux unless you pay a good deal of money for it.
> Mark Kendall has started on an OpenGL video renderer which
> should allow us to implement some really slick deinterlacers
> in hardware. But this isn't very far along yet and we will
> not be writing an XvMC replacement in OpenGL fragment
> programs anytime soon; we may eventually do this since it
> doesn't look like nVidia will be adding MPEG-4 AVC support
> to XvMC...
Just to add, I have no intention of using anything but MythTV! :P
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