Re: Digital negative novice needs help.

----- Original Message -----
From: "Gregory Popovitch" <greg@gpy.com>
To: <alt-photo-process-l@usask.ca>
Sent: Friday, April 21, 2006 6:35 AM
Subject: RE: Digital negative novice needs help.

> Ctein's excellent book Post Exposure has a chapter talking
> about this.
> He does say that even though the eye may not resolve more
> than 10 lp/mm,
> it can clearly see a difference betwenn a print resolving
> 20 lp/mm and
> one resolving 60 lp/mm. He says that it is because human
> vision doesn't
> just resolve fine detail, it selects for and analyses edge
> detail. The
> human eye can see whether edges are blurry even in the
> finest
> observable detail.
>
> The conclusion is that a print has to resolve at least 30
> lp/mm for
> "perfect" sharpness (that's probably not quite applicable
> to matte prints
> on textured papers).
>
> gregory
>
   I am not sure this is true. The visual system does judge
sharpness from edge contrast but increased resolution does
not necessaryly mean the edge contrast is greater. The
"acutance" effect in film is an example. Acutance is a
measure of perceived sharpness. In film it is increased by
exagerating edge/border effects. The result is an increase
in edge sharpness but often a reduction in actual resolution
because of the distortion at the edges.
   Ctein has a lot of good stuff in his writings but also
shows a lamentable lack of rigor and willingness to
extrapolate from the known to the imaginary.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com