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Re: Photo Image out of focus

At 06:10 6/20/01 -0400, Larry wrote:
You quickly find that the enlarger can make the image even more *out* of
focus, but there is no purely optical way to make the image more *in*
focus than it is on the negative. Not even with all the king's horses
and all the king's men :-) [I don't thinks it's technically an
entropy example, but it acts like one.]

The darkroom process is classic converging lens optics with a "real
image" produced. If you do some ray diagramming you soon see why a lens
can't reconstruct a sharp image from a blurred negative. With purely
optical 2D rendering, the best you can hope for is an accurate rendition
of the immediate source. It is truly a "garbage in, garbage out"

Best wishes,


Larry Cartwright

Larry possibly puts the case too strongly against purely optical
reconstruction. With the Beeb refresher in mind, I visualize this.

1) From the (defocused) image of a point, generate a 2D point spread
function filter from its optical Fourier transform.
(i.e) Place the defocused point image at the front focus of a laser
illuminated field. Hence the FT filter is available at the back focus.

2) take a reversal image of the PSF FT filter generated by 1)
[This step is to generate an inverse point spread function filter, I hope!]

3) With the blurred image at the front focus, and the inverse FT PSF filter
at the back focus, FT the convolved image through a second lens to produce a
(somewhat) deblurred image at the back focus of the second Fourier
transforming lens.

You will notice this is a monochromatic process. To have a chance to sharpen
color images, three seperations would be needed.

(The foregoing discussion is entirely speculative)

brian whatcott <> Altus OK