Resolution of human eye?

F. Frank LeFever flefever at ix.netcom.com
Sat Jan 18 21:37:32 EST 1997


In <82vi8vn9gr.fsf at manic.eecs.umich.edu> Michael Hucka
<hucka at eecs.umich.edu> writes: 
>
>>>>>> 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

Let me just insert something left out of the detailed reply to this
query (v. infra):  the resolution is better than its optics say it
should be, because of neural mechanisms for sharpening the otherwise
blurry image.  "Lateral inhibition" is the key term (principle seems
general, not just in the retina).  Cells in the center of a blurry
projection are not only getting slightly more light than those off
center, but are enhancing the difference by inhibiting the activity of
those off-center.

I believe there are also some studies showing the value of slight
movements of the eye in sharpening and/or maintaining sharpness,
filtering out "noise" etc., but this is only a vague recollection of
something  I may have read and not understood well at the time!

Frank LeFever
New York Neuropsychology Group








>  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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