Archived posting to the Leica Users Group, 2009/06/04

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Subject: [Leica] Why sharpen?
From: clive.moss at gmail.com (Clive Moss)
Date: Thu, 4 Jun 2009 08:53:08 -0500
References: <036901c9e3d8$fe810840$fb8318c0$@net> <4cfa589b0906032137l56e84d60j21c6f5d63bfc00b8@mail.gmail.com> <007301c9e514$40f626b0$c2e27410$@net>

Digital use sharpening in the following three cases - two of them
"required", one discretionary.

1 - Capture Sharpening: At the time of capture, each pixel is a discrete
distance from its neighbors. Anti-aliasing techniques, whether physical or
using software, are required to avoid the generation of artifacts like moire
patterns. The interpolation required by the capture process causes the dark
side of each edge to get lighter, and the light side to get darker.
Sharpening compensates for for this effect.

2- Creative sharpening: Never required, but occasionally useful. Analogous
to rubbing on the print or breathing heavily on a local area to increase
local contrast

3- Output sharpening: To compensate for the blurring of edges induced both
by another round of digitization and the randomness of the of the blobs of
ink as they leave the print head and spray onto the paper. The process
darkens the dark side and brightens the bright side of each edge to offset
the opposite direction lightening and darkening effect of the printing
process.

Future generations will marvel at the "requirement" that analog techniques
have that one has to remove the sensor from the camera and run it through
several processing stages involving smelly liquids before seeing an image.
"Why not simply lift the image off the sensor in the camera" they will say.

In the long run, I suspect that digital deconvolving techniques will improve
to allowing increasing depth of field to compensate for serious focusing
errors - and probably be built into the camera or raw converter.
--
Clive
Blog:  http://clive.moss.net/blog
Photographs: http://clive.smugmug.com


On Thu, Jun 4, 2009 at 7:59 AM, Frank Filippone <red735i at 
earthlink.net>wrote:

> ...
> What I do not understand is why digital "requires" sharpening, when for the
> past 150 or so years, film did not.
>
> Or was it that film did not have this facility ( other than some pretty
> obscure and relatively rarely used masking techniques) and digitally, the
> facility is only a mouse click away?
> ...


In reply to: Message from red735i at earthlink.net (Frank Filippone) ([Leica] Why sharpen?)
Message from abridge at gmail.com (Adam Bridge) ([Leica] Why sharpen?)
Message from red735i at earthlink.net (Frank Filippone) ([Leica] Why sharpen?)