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From: poynton@vector.Eng.Sun.COM (Charles A. Poynton)
Newsgroups: comp.fonts
Subject: Re: PostScript vs TrueType?
Summary: Colloquial "Square pixel" refers to aspect ratio, not PSF.
Message-ID: <140606@sun.Eng.Sun.COM>
Date: 14 Aug 90 05:17:52 GMT
References: <1100.26af57d3@waikato.ac.nz> <1990Jul26.135834.9874@tsa.co.uk> <388
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Reply-To: poynton@sun.com (Charles A. Poynton)
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This message was automatically generated by a filter that detected the
phrase "square pixel" in UseNet news message <1468@chinacat.Unicom.COM>
writen by woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) on 8 Aug 90
02:49:46 GMT.

"Square pixel" has acquired a colloquially meaning, namely, that samples are
equally speced horizontallly and vertically (e.g. 300 dots per inch, both
directions).  A more precise term is "unity sample aspect ratio".  

This widely-accepted interpretation has no relationship to the distribution
of energy associated with one pixel, properly known as point-spread
function.  

Someone is Boston told me he once tried to build a CRT monitor whose
electron beam was square in cross section; predictably the pictures looked
terrible.  A precise term for this would be "box-shaped point spread
function", in contrast to the more usual "gaussian point spread function" of 
a CRT or (I suppose) cylindrical PSF of a laserwriter.  

C.