Re: Photo Image out of focus

[brian whatcott <inet@INTELLISYS.NET>]

At 21:38 6/22/01 -0400, Ludwik wrote:
> Let us consider a simple case, a source (object) is a set of four
> equidistant points along a line segment. Or, to be more realistic,
> it is a set of four segments. Under proper focusing the image
> would consist of 20 distinct small circles forming a grid. But
> the lens was not focused and each circle is very large. The 20
> circles overlap very significantly and the intensity  distribution
> is a rectangular blab with round corners.
>
> An observer wants to determine the distribution of sources in
> the image plane. Under what condition would s/he be able to
> determine that the number of point-like sources was 20 and
> the distances between them were 3 cm, for example?...

I can think of some helpful conditions - an emulsion latitude
capable of capturing the intensity contributions of several
source contributions - I seem to recall the appropriate measure
of this property is the Hurter-Driffield curve. The fact that
it *is* a curve is unhelpful.

 Though I suggested the need for a specimen image of a point source
as a ready means of developing an inverse point spread function,
I see that recent efforts in this general area which are directed to
evaluating the relative distances of various objects in a field of
 view by means of their differential  blurring (which by all accounts
 is an accessible method) often avoid this prerequisite by subjectively
identifying a sharp edged object in the source, from its blurred
representation in the image. (We are after all, possessors of superior
pattern recognition clockwork...) This provides a sample of the point
spread or transfer function in one axis at least.

One would prefer that the blurred image is all captured - losing blurred
edges makes identifying a point from the blurred gestalt more chancy.

And there you have it, as a first blush response.


brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!