[rollei_list] Re: Digital Wins
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Fri, 15 Apr 2005 17:38:27 -0700
----- Original Message -----
From: "Jim Somberg" <jimsberg_04@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Friday, April 15, 2005 4:25 PM
Subject: [rollei_list] Re: Digital Wins
>I think that the bottom line is that I have seen very sharp
>edged digital pix at large sizes, that sort of pass as high
>resolution pictures- but regardless of the # of pixels in
>the digital camera, these pictures don't look right. With
>the sharpening software that is invariably used to achieve
>those results, things look decidedly oversharp, often with
>an unusually extended depth of field, and unnatural edges.
>It is particularly obvious in newspaper photos for the past
>year or more and in many product shots; the pictures appear
>to be superb at first look, looking like they came from
>8X10 sheet film, and slightly weird after the longer look.
>Someone made the point that sharpness is not the same as
>detailed and I believe they were right on.
> In other words, these pictures are probably OK for their
> intended short term uses, but somewhat dishonest in the
> long term and as gallery/wall prints. Ansel Adams would be
> appalled.
>
> Now, would you good fellows stop with all the daily emails
> and get back to your day jobs! (Just kidding, of course.)
>
> Jim Somberg
A possible explanation for the disagreements in this
discussion may be that one side is talking about resolution
and the other about the impression of sharpness. The latter
is a matter of perception by the eye. If edges are sharp and
high contrast the eye will interpret the image as sharp even
when it does not have much detail in it. In film this
quality is called acutance. It also exists in lenses where a
trade off can be made between resolution and contast. In
video edge sharpening, called edge enhancement, is an old
trick going back to the black and white days. Regular
television does not have very good resolution and does not
look sharp. The earliest method of enhancing edges was to
use a peaking filter in the video amplifer. This had the
effect of drawing lines around things. If used with some
restraint it improved the picture. More elaborate ways of
doing the same thing were used in color TV where resolution
can be very low. Digital TV often employs digital
compression which destroys resolution but lots of edge
enhancement is used to fool the eye into seeing a sharp
image. When I watched the recent Olympics in so-called high
definition TV, I was appalled by how bad it was. This was a
Direct-TV feed from NBC. The amount of compression was so
high that it could not render the motion at all and the
still images looked like what used to be called coring. In
fact, it looked very much like a VHS machine operating in EP
mode.
While the compression methods and effects in TV is
different than in still digital cameras there are still
similar artifacts from too much compression or not enough
data to begin with.
I am not quite sure how pixels are accounted in still
cameras, or what method of translating from film resolution
to digital resolution is valid.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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