Resolution of human eye?

Michael Hucka hucka at eecs.umich.edu
Fri Jan 17 18:55:00 EST 1997


>>>>> On 16 Jan 1997, ericsson at acsu.buffalo.edu wrote:

  ericsson> In the course of buying a gel documentation system, and
  ericsson> considering the various camera options that include differences
  ericsson> in the resolution of the camera, the most common being 768 by 494
  ericsson> pixels (and 8 bit greyscale), the question came up: What is the
  ericsson> resolution of the human eye? This is what will finally limit the
  ericsson> useful resolution (at the desired output magnification). This
  ericsson> would be determined by the number of light sensitive cells per
  ericsson> unit area of retina and the closest point you can hold an object
  ericsson> to your eyes, and still focus (which will vary with age).

The receptor spacing on the retina is not the only thing that determines the
resolution of the human eye.

First, the receptor density is highly variable; it varies based on the
position on the retina where it is measured (receptor spacing is shortest in
fovea and increases as you move outward from the retina) and it varies by
individual.  Second, the optics of the eye have an effect on the "resolution
of the human eye".  It turns out, for example, that the resolution that you
can calculate based on average foveal receptor spacing is somewhere around
60-65 cycles per degree, but the optics of the eye reduce the average
*usable* resolution somewhat.  This is because the lens blurs the image, like
low-pass filtering.  Third, usable resolution in a given situation is
affected by amount of light available and the contrast of the pattern being
viewed.

That said, I believe that the usual number quoted for resolution under
optimal conditions, for the minimum separation between the centers of
adjacent dark and light bars, is about 0.5 minute of arc.

Two books that talk about this are:

       AUTHOR = {Russell~L. {De Valois} and Karen~K. {De Valois}},
        TITLE = {Spatial Vision},
    PUBLISHER = {Oxford University Press},
         YEAR = 1990,
      ADDRESS = {New York},
         NOTE = {Originally published in 1988.},

       AUTHOR = {Vicki Bruce and Patrick~R. Green},
        TITLE = {Visual Perception: Physiology, Psychology and Ecology},
    PUBLISHER = {Lawrence Erlbaum \& Associates},
      ADDRESS = {London},
         YEAR = 1985,

Interestingly enough, this question was asked a couple of months ago on
sci.image.processing.  You may still be able to find the discussion thread in
DejaNews (http://www.dejanews.com); search for "What resolution is the human
eye?".

-- 
Mike Hucka     hucka at umich.edu     <URL: http://ai.eecs.umich.edu/people/hucka>
 PhD to be, computational models of human visual processing (AI Lab) University
    UNIX systems administrator & programmer/analyst (EECS DCO)      of Michigan



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