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Sharpening [was Re: Resolution and print quality]



Kennedy (& Harvey),

I hesitate to continue this discussion, having been doing serious
photography for only a couple of years, and being a scientist rather than an
arts person. However, I don't agree that the only sharpening required is
that necessary to replace that lost during scanning etc. This might be the
case if your photography is of the 'record picture' type - trying to
reproduce exactly the scene in front of the lens. But I don't think that is
what most 'serious' photographers do. They 'enhance' their images, by every
physical, chemical, and electronic trick in the book, to try to produce an
unreal picture that satisfies their artistic interpretation of the scene.
Enhancement of edges - sharpening - is surely just one of those tricks.

Painters have for a long time known that to enhance edges you lighten the
paint on one side of an edge and darken it on the other. I was at an
exhibition of paintings by Picasso, Matisse, etc only a few weeks ago -
"Paris in the 20's" I think it was called - and I remember saying to my wife
"Look at that marvellous example of the use of 'unsharp masking'. Looking at
the paintings and prints of paintings in my house, I can see numerous
examples of where the artist has emphasized an edge - to make it stand out
from the background. And yes, if you peer at the paintings from 10" they
look unreal, but stand back and you enjoy the effect the artist was trying
to achieve.

A friend of mine who goes to art classes has been taught how to enhance
edges by painting a darker line round the inside of the edge to make the
object stand out - asymmetric sharpening (you can do this with usm on a
layer by setting Blend mode to Darken).

With our new computer techniques, sharpening can be done by various means;
usm is just one of them. But I maintain it is a valid artistic technique to
make an object stand out, and that the amount of it that you need depends on
the effect you want and on the viewing distance. An artist painting
miniatures does so with delicate strokes and lines suitable for a close
viewing; an artist painting murals uses larger brushes and strokes more
appropriate for viewing at a distance.

The fault that many photographers perhaps have is of applying an equal
amount of sharpening to the whole image. Painters don't seem to do that;
they are more selective in what they sharpen and by how much. I have
recently started being much more selective; one recent image that needed
different amounts of sharpening in different areas was sharpened four times
with 100% amount of usm. Then, using the History brush, I simply painted the
appropriate amount of sharpening into the different areas of the image.

But all done for a viewing distance of 10 feet or more, which is what
happens if I show my prints to a seated audience. Forget the fine detail if
people are sitting 20 feet away; it's the overall composition and impact
that counts. IMO.

Bob Frost (awaiting the flak)

----- Original Message -----
From: "Kennedy McEwen" <rkm@kennedym.demon.co.uk>
> >
> IMO, sharpening is a process to compensate for losses in the image
> capture and reproduction process, to return the image to a closer
> approximation of 'reality'.  Consequently, images which are viewed at a
> distance should, in principle, require LESS sharpening, because they
> already approach the ideal with the finest details being just resolvable
> and the limitations of the capture process invisible in any case.
>
> One of the main reasons for making an image large to be viewed at a
> distance is that it appears to have the same spatial spectrum content as
> a real scene, governed only by the limitations of your eyes, otherwise
> you might as well make it suitable for viewing at the normal 10" relaxed
> close viewing distance.  Sharpening such an image makes it look false
> and synthetic, and I would guess that this is exactly the sort of effect
> that Harvey (and myself!) finds objectionable.


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