Just wondering - if a lens is not very sharp it acts essentially as a
low pass filter. If this analogy holds, applying some sharpening in
post-processing (essentially a high pass filter) should compensate for
the lack of sharpness of the lens, right?
Of course sharpening also amplifies the noise, but if noise levels are
low anyway, for instance because the image was captured at lowest ISO
with a DSLR, the additional noise shouldn't be an issue.
--
"Alfred Molon" <alfred_molon@yahoo.com> wrote
news:MPG.22df3f654d4d098398bd4c@news.supernews.com ...
>
> Just wondering - if a lens is not very sharp it acts essentially as a
> low pass filter. If this analogy holds, applying some sharpening in
> post-processing (essentially a high pass filter) should compensate for
> the lack of sharpness of the lens, right?
>
> Of course sharpening also amplifies the noise, but if noise levels are
> low anyway, for instance because the image was captured at lowest ISO
> with a DSLR, the additional noise shouldn't be an issue.
> --
>
> Alfred Molon
> ------------------------------
> Olympus 50X0, 8080, E3X0, E4X0, E5X0 and E3 forum at
> http://tech.groups.yahoo.com/group/MyOlympus/
> http://myolympus.org/ photo sharing site
MY experience has been that a SMALL amount of sharpening (preferably
unsharp-masking) is acceptable in the stated situation. More looks
artificial and will introduce artifacts.
An unsharp lens is a LOSSY low-pass filter. Sharpening after the fact will
do little.
In article <1215638971.761781@athprx03>, G Paleologopoulos says...
> MY experience has been that a SMALL amount of sharpening (preferably
> unsharp-masking) is acceptable in the stated situation. More looks
> artificial and will introduce artifacts.
> An unsharp lens is a LOSSY low-pass filter. Sharpening after the fact will
> do little.
What do you mean by lossy?
In some cases it makes a huge difference if you apply some sharpening
during RAW conversion as opposed to not applying any sharpening.
--
"Alfred Molon" <alfred_molon@yahoo.com> wrote
news:MPG.22df52eb35aa3e5998bd4f@news.supernews.com ...
>
> In article <1215638971.761781@athprx03>, G Paleologopoulos says...
>
>> MY experience has been that a SMALL amount of sharpening (preferably
>> unsharp-masking) is acceptable in the stated situation. More looks
>> artificial and will introduce artifacts.
>> An unsharp lens is a LOSSY low-pass filter. Sharpening after the fact
>> will
>> do little.
>
> What do you mean by lossy?
>
> In some cases it makes a huge difference if you apply some sharpening
> during RAW conversion as opposed to not applying any sharpening.
> --
>
> Alfred Molon
> ------------------------------
> Olympus 50X0, 8080, E3X0, E4X0, E5X0 and E3 forum at
> http://tech.groups.yahoo.com/group/MyOlympus/
> http://myolympus.org/ photo sharing site
OK, I meant that as a result of "unsharpness" some original information
(which would be recorded by a sharper lens) is irretrievably lost, no matter
what follow-on procedures one uses.
Rgrds, G.
On Jul 9, 4:35 pm, Alfred Molon <alfred_mo...@yahoo.com> wrote:
> Just wondering - if a lens is not very sharp it acts essentially as a
> low pass filter. If this analogy holds, applying some sharpening in
> post-processing (essentially a high pass filter) should compensate for
> the lack of sharpness of the lens, right?
>
> Of course sharpening also amplifies the noise, but if noise levels are
> low anyway, for instance because the image was captured at lowest ISO
> with a DSLR, the additional noise shouldn't be an issue.
> --
>
> Alfred Molon
> ------------------------------
> Olympus 50X0, 8080, E3X0, E4X0, E5X0 and E3 forum athttp://tech.groups.yahoo.com/group/MyOlympus/http://myolympus.org/photo sharing site
I find I use different sharpening levels for the different lenses I
use, both my 55 micro and 105 micro don't require much help. I use
Smart Sharpener in Photoshop and find it much better an easier than
Unsharp mask. I had used Nik Sharpener before PS added Smart
Sharpener. A level of 70 with a radius of .9 works well with the macro
lenses. With my old 70-210 f4 I use a level of 95 with a radius of .9
to 1.4, my other lenses fall in between. Photographed a waterfall at
f16 a couple of weeks ago and because of the diffraction I ended up
pushing the sharpening to 1.6 at 120 and this helped the image, kicked
myself for not having an ND filter with me.
On Jul 10, 4:10*am, "G Paleologopoulos" <gpa...@ath.forthnet.gr>
wrote:
> "Alfred Molon" <alfred_mo...@yahoo.com> wrotenews:MPG.22df52eb35aa3e5998bd4f@news.supernew s.com...
>
>
>
>
>
> > In article <1215638971.761781@athprx03>, G Paleologopoulos says...
>
> >> MY experience has been that a SMALL amount of sharpening (preferably
> >> unsharp-masking) is acceptable in the stated situation. More looks
> >> artificial and will introduce artifacts.
> >> An unsharp lens is a LOSSY low-pass filter. Sharpening after the fact
> >> will
> >> do little.
>
> > What do you mean by lossy?
>
> > In some cases it makes a huge difference if you apply some sharpening
> > during RAW conversion as opposed to not applying any sharpening.
> > --
>
> > Alfred Molon
> > ------------------------------
> > Olympus 50X0, 8080, E3X0, E4X0, E5X0 and E3 forum at
> >http://tech.groups.yahoo.com/group/MyOlympus/
> >http://myolympus.org/photo sharing site
>
> OK, I meant that as a result of "unsharpness" some original information
> (which would be recorded by a sharper lens) is irretrievably lost, no matter
> what follow-on procedures one uses.
> Rgrds, G.
Also, the sharpening filter has no way to distinquish between a sharp
edge that has been rounded off by optics, and an edge that was already
gradual. It sharpens both.
Don Stauffer in Minnesota wrote:
[]
> Also, the sharpening filter has no way to distinquish between a sharp
> edge that has been rounded off by optics, and an edge that was already
> gradual. It sharpens both.
Wouldn't applying the appropriate inverse MTF function restore the loss of
sharpness (up to the spatial frequency when the signal is lost in the
noise)? I accept that the so-called sharpening filters are not the
correct approach - if they are non-linear operators.
In article <5apdk.24338$E41.6360@text.news.virginmedia.com> , David J
Taylor says...
> Wouldn't applying the appropriate inverse MTF function restore the loss of
> sharpness (up to the spatial frequency when the signal is lost in the
> noise)? I accept that the so-called sharpening filters are not the
> correct approach - if they are non-linear operators.
That was my idea. The assumption I made was that unsharp mask would
approximate this inverse MTF function.
In any case, this inverse MTF filter would have to be tailored for the
lens and know for instance that the lens is more sharp in the centre
than at the edges (i.e. apply more sharpening in the centre) and know
the sharpness characteristics at different focal lengths and apertures.
I think there could be a generic "inverse lens blur" filter which would
have to be calibrated with a number of shots of a test target.
--
Alfred Molon wrote:
> In article <5apdk.24338$E41.6360@text.news.virginmedia.com> , David J
> Taylor says...
>
>> Wouldn't applying the appropriate inverse MTF function restore the
>> loss of sharpness (up to the spatial frequency when the signal is
>> lost in the noise)? I accept that the so-called sharpening filters
>> are not the correct approach - if they are non-linear operators.
>
> That was my idea. The assumption I made was that unsharp mask would
> approximate this inverse MTF function.
>
> In any case, this inverse MTF filter would have to be tailored for the
> lens and know for instance that the lens is more sharp in the centre
> than at the edges (i.e. apply more sharpening in the centre) and know
> the sharpness characteristics at different focal lengths and
> apertures.
>
> I think there could be a generic "inverse lens blur" filter which
> would have to be calibrated with a number of shots of a test target.
Alfred,
I think you may need to be careful exactly which "sharpening" method you
use. Some are non-linear (and non-reversible) and are not purely MTF
changes. Agreed about MTF changes over the image area.
Having said all that, when people refer to a "tack sharp" image, I suspect
that they actually mean over-sharpened, i.e. a net response which is
higher in the spatial frequency region where the eye is most
sensitive.....
Sharpening when the lens is soft 
Linear Mode
