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From: k9ape@eecs.nwu.edu (Sheldon L. Epstein)
Subject: Re: RS170/NTSC video->non-square pixels?
Message-ID: <D2rzBJ.CrA@eecs.nwu.edu>
Keywords: RS170,NTSC,capture
Sender: usenet@eecs.nwu.edu
Organization: EECS Department, Northwestern University
References: <3fn84v$sa@news.arc.nasa.gov>
Date: Sat, 21 Jan 1995 21:50:06 GMT
Lines: 42

In article <3fn84v$sa@news.arc.nasa.gov>,
Kevin Montgomery <kevin@neuron.arc.nasa.gov> wrote:
>Hi folks-
>	a somewhat subtle question.  When you digitize (frame grab) an
>RS170 signal, are the resulting pixels square?  I'm trying to extract
>quantitative information from such images and I just had the terrible
>thought that, since RS170 doesn't specify square pixels, the framegrabber
>may not take this into account (worse yet- it could be implementation 
>specific).  Does anyone know for sure what the deal is?
>
>						thanks in advance...
>

Hello Kevin,

RS-170 refers to video levels - not pixel geometry.  Assuming that you
purchased an NTSC-compatible camera for use in North America, then you 
frame grabber will see 525 lines/frame - 45 line/vertical retrace =
480 video lines/ frame.  Each line will probably have 512, 640 or 752
pixels - depending on the pixel clock rate of the camera.  Hence each
pixel is taller than it is wide.

If you want square-pixel cameras, then you need PAL-compatible cameras
which are generally used in Europe; but are available here.  Examples
are SONY XC-Series cameras with model numbers ending in CE - i.e.
XC-77RRCE.  Most monitors sold in the USA won't sync to them; however,
monitors such as the SONY PVM-1344Q monitor have detector switches
that will switch the monitor from NTSC to PAL.

Imaging boards such as EPIX (epix@interaccess.com) will accept both
NTSC and PAL cameras - plus many other formats - and have software
which will allow you to switch the board's performance.  In the
case of EPIX boards, you can use a PAL camera as an input and an
NTSC monitor as as output display.

If you are going geometric or morphological analyses (which we do
here) then you have to tell the software the pixel aspect ratio.
I suggest that you start at about 1.16:1.

Have fun and drop me a note if I can be of further assistance.

		Shel Epstein, k9ape@eecs.nwu.edu
