Re: capture card recomendations

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On Fri, 19 Dec 2003, Michel Bardiaux wrote:

> Trent Piepho wrote:
> > The bt8x8 chip samples the video stream at a high horizontal resolution.  I
> > know that for NTSC, it's 756 pixels.  I guess for PAL, it's 924.  
> > 
> > If you request less than full resolution, the bt8x8 scales the image down in
> > hardware using a number of different filters.  You even control the filters it
> > uses, but I don't think v4l has the ability to set these things.
> > 
> 
> I prefer software downscaling because what the hardware does is very 
> hardware-dependent. The hardware scaling wirks better with some cards 
> than others, and you dont have any control over it. And I did not find 
> statifactory documentation. For power-of-two downscaling, the quality 
> obtained by simple decimation was found acceptable by all my guinea pigs.

I doubt you'll find any hardware the does worse scaling than simple
decimation.  I have a hard time thinking of what that would be....

> But I let the card do whatever is necessary to give me a 'standard' 
> full-size image. The 704x576 was derived from SIF. I found contradictory 

With a bt8x8 at least, when you request a 704x??? image the card is already
scaling it for you.  The bt8x8 ALWAYS horizontally scales your image.  You're
just scaling it again in software.




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