Archived posting to the Leica Users Group, 2006/05/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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 . . . -- ___________________________________________________ Play 100s of games for FREE! http://games.mail.com/ _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information