Archived posting to the Leica Users Group, 2006/05/12

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Subject: [Leica] Bokeh and quantification
From: jsmith342 at cox.net (Jeffery Smith)
Date: Fri May 12 19:03:23 2006

Ah, the results always go back to the person doing the looking. I have
always felt that way about stereo speakers. I saved and saved for some AR3a
speakers in the early 70's based on their faithful reproduction of sound.
But when I heard the Cerwin Vega speakers in the same room (for half the
price), I was blown away.

I feel the same about chardonnay that is supposed to taste good.

Jeffery Smith
New Orleans, LA
http://www.400tx.com




-----Original Message-----
From: lug-bounces+jsmith342=cox.net@leica-users.org
[mailto:lug-bounces+jsmith342=cox.net@leica-users.org] On Behalf Of Marty
Deveney
Sent: Friday, May 12, 2006 8:53 PM
To: lug@leica-users.org
Subject: [Leica] Bokeh and quantification


I have just finished reading a thesis in which bokeh is quantified
precisely.  The system is based on a series of identical digital black and
white images, taken with three lenses (they happen to be large format
because of the scanning back that she used but could be any lenses) at
various apertures and focal distances - the pixel distribution was then
measured around key in- and out-of-focus areas (to capture a representative
range of parts and characteristics of the image).  This could be done with a
film image by fine-scale densitometry, so the system is not just applicable
to digital images.  She then used a dissimilarity index to compare the
points.  This resulted in a graph that quantifies the changes in pixel
distribution from near to far for a given aperture.  That part of the method
quantifies _what_ the bokeh looks like at that aperture.  The different
apertures are then compared using a scaling analysis that provides a
three-dimensional representation  of dissimilarity - a virtual, mathematical
representation of the bokeh, if you like.  If you superimpose these plots
from the three different lenses, you have an absolute representation of the
differences in bokeh. 
So it can be done, even if it took a year to do it for three lenses.  The
method Canon uses is simpler and less precise than this, but does also
capture it effectively.

So it can be done.  The student did mention in her discussion, however, that
while the method was sound and proved bokeh could be measured, that bokeh
was probably best judged visually by the photographer . . .

-- 
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Replies: Reply from dlridings at gmail.com (Daniel Ridings) ([Leica] Bokeh and quantification)
In reply to: Message from freakscene at weirdness.com (Marty Deveney) ([Leica] Bokeh and quantification)