[tig] Human Vision

kenneth.r.rockwell at exgate.tek.com kenneth.r.rockwell
Wed Dec 24 17:00:25 GMT 2003


I have always heard the 1 arc minute number.  It refers to astronomical
resolution, meaning if you take two bright dots they will look like one dot
if they are closer than that, and two barely discernable dots if further
away than that.

The math involved to correlate that to pixel pitch is beyond me on Christmas
eve.  Please let us all know if you get to the bottom of this.  Remember
too, that with a rectangular grid you have the pitch varying by 40%
depending on angle (vertical or diagonal).

I would test this on myself by putting up alternating on/off pixels on a
screen and seeing how far back I can see lines as opposed to gray.  I have a
Photoshop file I made for this if anyone wants it. (Actually made the file
for matching pixel clocks on projectors' capture cards to my PC)

I do know others have spent far more time than I have.  A photographic
author called Ctein did some investigation in a magazine called "Photo
Techniques" into photo print sharpness and resolution in lines per mm on
paper.  He discovered that even though humans could not see lines spaced
more closely than a certain amount of lpmm, they could detect differences
between a sinusoidally varying intensity distribution and a square wave
function (I presume he had similar RMS modulation depths so it was not
simply great RMS amplitude for the square wave).  This stuck him as
rightfully curious, since it suggested that we somehow were sensitive to
spatial harmonic content above the limiting resolution.  Curious, and no one
has researched that as far as I know.

Google finds lots of pages on this, for instance
http://clarkvision.com/imagedetail/eye-resolution.html

Ken Rockwell
Tek
www.KenRockwell.com

-----Original Message-----
From: Steve Shaw [mailto:digital.praxis at virgin.net]
Sent: Wednesday, December 24, 2003 8:36 AM
To: TIG
Subject: [tig] Human Vision


thanks Mike Chiado for supporting the TIG.
--

Ok, here's something a bit more interesting.
I'm attempting to research the capabilities of the human eye with respect to
resolution...
 From what I can find is seems that the average human eye can see a maximum
separation of 1 arc minute per line pair to visualise point separation.
So, this suggests that an average cinema with a viewing angle of 30 degrees
from the best seat in the house (as seems to be the normal SMPTE spec) would
require 30x60/1=1800 pixels to match the maximum resolution of the human
eye.

Is this correct? Seems a bit too simple to me.

Steve

Steve Shaw
Digital Praxis Ltd
The Granary
Throcking
Buntingford
Herts SG9 9RU
+44 (0)1763 281 699: f
+44 (0)7765 400 908: m
steve at digitalpraxis.net
www.digitalpraxis.net


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