Re: [Motion-user] BTTV NTSC Resolution Question

[Gordon <gc...@tr...>]

Thanks for the help - I tried 640x480 for the first time and it works great.

When I sampled different resolutions before, I was using what I read 
were different NTSC resolutions. It never occurred to me to try 640x480 
because NTSC has odd resolution steps (352x288 -> ?? compared to webcam 
320x240 -> 640x480 which is doubled). My thinking was that it had to be 
an odd number. A Google search for NTSC and RESOLUTION will bring up a 
lot of different settings all of which are related to an NTSC 
specification, but none of which worked.

What I wrote in the original message was wrong: These odd resolutions I 
tried prevented the thread from starting.

640x480 works great and is very sharp. I also tried what I saw was the 
resolution of the deinterlace demo pictures (512x384) and I was 
surprised to see that the tread worked with those, too. 640x480 looks 
better as expected. I wonder why those deinterlace patch demo pictures 
are 512x384 and not 640x480, because my player shows my 640x480 movies 
really are playing at 640x480. I would think a frame grab would be the 
same resolution.

This made me wonder if 640x480 really the exact optimal resolution for 
an NTSC camera in high-res. It is with an Axis 2100 netcam, for example, 
if you have the 2100 set to 640x480.  In that case it's easy because you 
simply match in Motion (and Cambozola) the resolution set in the camera.

With an interlaced, analog NTSC camera it doesn't appear to be as simple 
to get a direct one-to-one match.  If it was, 704x576 would be exactly 
right because it's 352x288 doubled (the thread won't start with 704x576).

Also, NTSC cameras of different TVL ratings seem as if they should be 
set to different BTTV/Motion resolutions; higher TVL = greater 
resolution. Instead it looks like you set both to 640x480 and the higher 
TVL rating camera will have a sharper picture; you get higher quality 
(sharpness) but not higher quantity (resolution).

This makes sense given the BTTV chip takes a 60+ year old analog video 
specification and does its best to convert it into something a computer 
can use.  The 640x480 resolution setting (the apparent high-end limit) 
must be a product of the BTTV chip and driver, something high enough to 
get all the quality an NTSC camera can deliver but a resolution 
specification common to the computer industry. Then they fill in that 
640x480 space with whatever image the camera delivers.

Andrew Hamilton wrote:
> On Wednesday 22 March 2006 8:00 am, Gordon wrote:
> 
>>;width 352
>>;height 288
> 
> 
> Do you uncomment these when you change their value?  That is the only thing 
> that catches my eye at the moment.
> 
> Sincerely,
> Andrew Hamilton
> 
> 
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