Date   : Sun, 04 Apr 2004 12:15:10 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: Aspect ratio question

"Thomas Harte " <thomasharte@...> wrote:
> pixels. Which was very silly of me. What I was thinking was: a square
> which takes up m/nths of the horizontal area of the screen needs to occupy
> m*4/n*3ths of the vertical area to be genuinely square.
> 
> Therefore pixels are only 12/13ths as wide as they should be. Now, recall
> that earlier I asserted that you'd want to use 45/52ths of the displayed
> width of a 4:3 screen to display BBC graphics at the correct aspect ratio
> if you had scaled the image so that the entire height of the output was
> occupied by BBC graphics? Whereas you maintain that 30/32nds is the way to
 
Hold on, hold on!  Aren't you all going about this the wrong way round? 
You're assuming you have perfect display equipment and perfect optical
receptors. Even for translating a display via emulation your are still
assuming that the host hardware is displaying on a perfect display.
 
What we always used to do was (and what I still do):
 
Draw a square:
MODE 0
MOVE 128,0:DRAW 1279-128,0:DRAW 1279-128,1023:DRAW 128,1023:DRAW 128,0
 
Carefully measure the displayed square. On my monitor here that's 168mm
each side.
 
And then carefully adjust the *MONITOR* to ensure the square was displayed
square.
 
If a square that has the same number of pixels on each side does not look
square, then there's a problem with the *MONITOR*.
 
And if you're going to argue PAL standards, then just wait until I get my
old television engineering textbooks out of the basement.
 
-- 
J.G.Harston (JGH BBC PD Library) 70 Camm Street, Walkley, SHEFFIELD S6 3TR
jgh@...                - Running on BBCs & Masters with SJ MDFS FileServer
Z80+6502/CoPro+Tubes/Econet+SJ - - - - - - - http://www.mdfs.net/User/JGH/