On Tuesday 19 December 2006 21:43, Hans Verkuil wrote:
> On Tuesday 19 December 2006 19:42, Trevor Bradley wrote:
> > I've just discovered the magic of the temporal filter on the
> > Hauppauge PVR cards (see my previous post). In brief, appears to
> > clean up a noisy analog signal to give a cleaner mpeg recording.
> > However, I note that there appear to be several other filters. If
> > I run "v4l2-ctl -l | grep filter" on my machine, I appear to get
> > parameters for:
> >
> >
> >
> > spatial_filter_mode (0),
> >
> > spatial_filter (0)
> >
> > spatial_luma_filter_type (1)
> >
> > spatial_chroma_filter_type (1)
> >
> > temporal_filter_mode (0)
> >
> > temporal_filter (8, was 0)
> >
> > median_filter_type (0)
> >
> > median_luma_filter_minimum (0)
> >
> > median_luma_filter_maximum (255)
> >
> > median_chroma_filter_minimum (0)
> >
> > median_chroma_filter_maximum (255)
> >
> >
> >
> > the numbers in brackets are my current settings for these
> > parameters.
> >
> >
> >
> > By simply changing my temporal_filter from 0 to 8, I saw a dramatic
> > improvement in image quality. This gets me thinking that modifying
> > these other numbers might be useful, but I've not found any
> > documentation whatsoever on these filters, and I'm hoping someone
> > might be able to enlighten me.
> >
> >
> >
> > Can anyone explain what the ivtv spatial, temporal, and median
> > filter settings actually do? Are they hardware or software
> > filters? What's the difference between the filter and the filter
> > type? What settings are appropriate for a TV? What numbers are
> > too high? (I noticed that a temporal filter setting of 10 caused
> > mpeg recording errors, and a max setting of 31 generated some
> > bizarre visual effects). Should this information be documented in
> > the wiki?
> >
> >
> >
> > This question belongs in ivtv-users, but the people who would be
> > able to answer the question are likely lurking in ivtv-devel.
> > Hopefully some of the developers read both groups.
>
> In the v4l-dvb repository (www.linuxtv.org) there is a qv4l2 tool in
> the v4l2-apps directory that lets you play with controls
> interactively.
>
> The best documentation is here:
> http://www.linuxtv.org/downloads/video4linux/API/V4L2_API/spec-single
>/v4l2.html#AEN807
There are three places where you can find API information: the
user-level API is either in the v4l2 spec (linked to above) or in the
driver source (esp. ivtv.h) for ivtv specific functionality. Eventually
everything should be documented in the v4l2 spec once the driver is
finally merged into the kernel.
Low level firmware documentation is kept in the kernel:
Documentation/video4linux/cx2341x. The most recent version is always
available in the v4l-dvb repository at www.linuxtv.org/hg/v4l-dvb.
Hans
>
> Basically the temporal filter is by far the most important. The
> spatial filter also has some effect, although the default value seems
> to be the best. I've never noticed any difference with the median
> filter and I suspect they are actually not implemented in the card's
> firmware.
>
> These filters are all done in hardware.
>
> Regards,
>
> Hans
>
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