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Date: Fri, 24 Feb 2012 23:54:25 +0000
From: Perry Mitchell <perry.mitchell@gmail.com>
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Subject: Re: [AE] OT resolution trivia
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On 24/02/2012 23:22, Chris Zwar wrote:
>   The reason we got stuck with 720 horizontal pixels and rectangular pixel aspect ratios lies in the maths behind that standard.  But it doesn't mean that analogue PAL and NTSC actually have 720 horizontal pixels, only that 720 is the agreed standard.
The reason it was chosen as 720 is that it was decided to have this 
common line sample size for both sides of the pond. It was a compromise 
between the 4:3 square pixel sizes of 640(648*) and 768. It may vaguely 
interest some of you that in fact the 720 samples cover more of the 
picture width than did the analog signals, the respective 'active 
picture' width being approximately 712 pixels for NTSC and 702 for PAL. 
It is only approximate because the analog timing specifications have a 
quite wide tolerance.
*note the true picture height for NTSC is 486 lines but many formats 
crop this to 480.
As intimated by Chris - analog TV (i.e. NTSC and PAL) don't have pixels. 
What is confusing for many is that both camera CCDs and display 
LCD/Plasma screens are all analog devices, but have an inherant digital 
sampling in the spacial domain.
Perry Mitchell