Sharpening

Is there anything better than unsharp mask to sharpen an image? More
specifically, to compensate for a not so sharp lens or a (small)
autofocus error.
--

Alfred Molon
------------------------------
Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

On Fri, 22 Mar 2013 23:38:33 +0100, Alfred Molon
wrote:

Is there anything better than unsharp mask to sharpen an image? More
specifically, to compensate for a not so sharp lens or a (small)
autofocus error.

Have you tried High Pass sharpening?
http://www.luminous-landscape.com/tu...arpening.shtml
--

Regards,

Eric Stevens

In article , Eric Stevens
says...
Have you tried High Pass sharpening?
http://www.luminous-landscape.com/tu...arpening.shtml

Just gave it a quick try and it doesn't seem to be better than USM.
--

Alfred Molon
------------------------------
Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

On 2013-03-23 11:33:44 -0700, Alfred Molon said:

In article , Eric Stevens
says...
Have you tried High Pass sharpening?
http://www.luminous-landscape.com/tu...arpening.shtml

Just gave it a quick try and it doesn't seem to be better than USM.

Using high Pass sharpening can be tricky, and it is very easy to over
do it ending up with an obviously over sharpened image, but done subtly
it can make an image "POP".
How bad is the OoF problem you are trying to fix?

Sometimes applying the USM selectively to the subject only, and
tweaking contrast and levels can differentiate the subject from the
background a little better. Even a bit of localized/selective
tone-mapping can help sometimes. However, for the truly OoF there is
little one can do to save the shot.

NIK have a few tools in Color Efex Pro 4 and NIK Sharpener Pro 2 which
might help.
Color Efex Pro 4 has a "Detail extractor" filter and a "Tonal contrast"
filter which have helped me with some of my problematic shots in the
past, and can be applied selectively.

Sharpener Pro 2 has a RAW "Pre-sharpener" and an output sharpener
neither of which I use, as to my eye the just seem to add too much
noise and don't really do the sharpening job I want.

If you care to post link to the problem file, either RAW or of
reasonable JPEG quality, I am sure that the tinkerers among us will see
if we can come up with a solution.

--
Regards,

Savageduck

In article 2013032312113764440-savageduck1@REMOVESPAMmecom, Savageduck
says...
How bad is the OoF problem you are trying to fix?

I was asking a generic question, and was curious to know to what extent
technology has progressed today.

Many cameras nowadays come with inbuilt reduction for vignetting,
chromatic aberrations and geometric distortions.
They might come one day (who knows?) with inbuilt deblurring, allowing
to automatically correct blurriness due to cheap lenses or small AF
errors.
--

Alfred Molon
------------------------------
Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

On 2013-03-23 12:40:02 -0700, Alfred Molon said:

In article 2013032312113764440-savageduck1@REMOVESPAMmecom, Savageduck
says...
How bad is the OoF problem you are trying to fix?

I was asking a generic question, and was curious to know to what extent
technology has progressed today.

Many cameras nowadays come with inbuilt reduction for vignetting,
chromatic aberrations and geometric distortions.
They might come one day (who knows?) with inbuilt deblurring, allowing
to automatically correct blurriness due to cheap lenses or small AF
errors.

OK! It was just that you said that you had tried High Pass filter
sharpening and you didn't find it any better than USM. So, I made the
assumption that there was a particular problem which needed fixing, not
a progress report on the digital processing wish list.

The quest for the perfect system continues. ;-)


--
Regards,

Savageduck

Alfred Molon wrote:
I was asking a generic question, and was curious to know to what extent
technology has progressed today.

Sharpening of digital images has not actually changed
any at all in literally decades (since well before
DSLR's were on the market).

There are exactly two basic forms that sharpening takes,
and everything else is just a mixture of the two or one
way or another to apply sharpen to only specific parts
of an image. That is, techniques such as "smart
sharpen", which usually means masking off only edges for
sharpening, or appling sharpening only to the luminance
channel in LAB mode, etc etc.

But there are significant distinctions between the two
basic kinds of digital sharpening that can be very
helpful to know about and understand. Unsharp Mask is
one type. What is best called High Pass Filter Sharpen
is the other (it should not be confused with the High
Pass Sharpen tool so titled by Adobe, which is
different.) Some people call it Convolutional Sharpen,
but USM can also use convolution so that is not a valid
distinction.

High Pass Sharpening, which I'll refer to as simply
"Sharpen" from this point on, uses a digital high pass
filter to detect high frequency spatial detail that
consists of a sequence of multiple tonal changes. Think
of a white picket fence outlined against a dark
background. Sharpen will increase the brightness of the
white parts and decrease the brightness of the dark
areas in between. Generally, the most change will be
made closer to the center of the tonal change. The
"amount" of change is one parameter and the "radius" (or
distance between edges, which is essentially the cutoff
frequency of the filter) is another, plus a third
parameter called "sigma" that is the distribution of the
change over the radius that is affected.

Visually, I=I=I=I=I=I is changed to this: | | | | | |

The way that Unsharp Mask works is different. It also
looks at tonal transition edges, but only single edges
and not multiple edges. The picket fence would be seen
as an average of the white pickets and the dark spaces
between, and considered just a single "grey" continuum.
But if there is an break in the fence (and open gateway,
for example), the transition from the average gray of
the fence on the left to the dark only background
through the gate would be seen as a transition, and then
on the other side the entirely separated transition from
the dark background to the average gray of the fence would
be seen also as a transition.

I=I=I=I=====I=I=I=I is changed to: I=I=I_H_===_H_I=I=I

Only the single transition is made more distinct

But it also has to be understood that the above represents the
"normal" adjustments for parameters. In fact USM parameters can
be set to see each picket in the fence, and the effect might be
somewhat similar for the two types.

But because USM will see a sequence as an average of the
values (that is where the "unsharp" in the name comes
from), the effects that it applies are irreversible. A
Sharpen tool is exactly the same algorithm that is used
for Blur, but with different parameters and either can
reverse the other.

The distinction between the two types comes into play
when an image from a camera that uses a Bayer Color
Filter is used. If no resampling is done, both types of
sharpening will probably have about the same effect and
almost any image will benefit from application of one,
the other, or both. After and image is down sampled
however, the effects of USM will usually be greater than
those of Sharpen. If the image is up sampled, the
effects of Sharpen will be greater than USM on most
images.

Note also that the higher the pixel resolution the
greater the amount and radius that is required to get an
effect.

The bottom line is that if you enlarge images for
printing it is very likely that Sharpen will be more
important than USM, while if you reduce images for web
display it is most likely that USM will be more
important than Sharpen.

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)

On 3/23/2013 2:33 PM, Alfred Molon wrote:
In article , Eric Stevens
says...
Have you tried High Pass sharpening?
http://www.luminous-landscape.com/tu...arpening.shtml

Just gave it a quick try and it doesn't seem to be better than USM.


If you switch to LAB mode, and sharpen only the lightness channel. This
will minimize halos.
First create a new layer so if you oversharpen you can back it down.
Also, if there are areas you don't want sharpened, you can mask them off.

--
PeterN

Eric Stevens wrote:

On Fri, 22 Mar 2013 23:38:33 +0100, Alfred Molon
wrote:

Is there anything better than unsharp mask to sharpen an image? More
specifically, to compensate for a not so sharp lens or a (small)
autofocus error.

Have you tried High Pass sharpening?
http://www.luminous-landscape.com/tu...arpening.shtml


Thanks for this pointer. It is my new favorite method of sharpening. Because
it is a layer, it is entirely reversible at any time, unlike USM.

This article
http://photo.tutsplus.com/tutorials/...h-pass-filter/

suggests a couple more interesting uses of high pass.

Thanks,
Doug

On 2013-03-31 10:41:18 -0700, Douglas Johnson said:

Eric Stevens wrote:

On Fri, 22 Mar 2013 23:38:33 +0100, Alfred Molon
wrote:

Is there anything better than unsharp mask to sharpen an image? More
specifically, to compensate for a not so sharp lens or a (small)
autofocus error.

Have you tried High Pass sharpening?
http://www.luminous-landscape.com/tu...arpening.shtml


Thanks for this pointer. It is my new favorite method of sharpening. Because
it is a layer, it is entirely reversible at any time, unlike USM.

This article
http://photo.tutsplus.com/tutorials/...h-pass-filter/

suggests

a couple more interesting uses of high pass.

Thanks,
Doug

One word of warning when using high pass filter sharpening, it is not
always the best choice for all sharpening tasks, and should be applied
with a subtle hand.
In images with strong textures, if one is not careful, it is easy to
over cook high pass sharpening, which results in artifacts noise, and
obvious over sharpening. At first look it might seem the image has
gained some "Pop", but on closer examination you will discover it is
over cooked.

So, unless you want that over cooked look try and keep the pixel radius
in the 2-6 range. If you start moving above a radius of 10 you will
start seeing artifacts in most images. Then you will get slightly
different results by your choice of layer blending mode. Your best
choices will usually be, "Overlay", "Soft Light", "Hard Light", or
"Vivid Light".

--
Regards,

Savageduck