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Lenses and sharpening



 
 
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  #1  
Old September 13th 14, 08:23 AM posted to rec.photo.digital
Alfred Molon[_4_]
external usenet poster
 
Posts: 2,193
Default Lenses and sharpening

Sometimes a soft lens can be very effectively compensated by some
unsharp mask in post processing and you get a sharp, natural looking
image.

But sometimes no matter how much sharpening you apply or what parameters
you choose, you get that unnatural, "sharpened" look.

It probably depends on the unsharpness of the lens, its (spatial)
frequency response or whether the sharpness is caused by the lens glass
itself (i.e. lens not being sharp enough), inaccurate focus or some
motion blur.

For instance I have a 70-300 lens which at the tele end generates a bit
soft images, which however respond well to unsharp masking in post-
processing. But that's not the case for the another lens I have (a mid-
range one).

Has somebody analysed this (i.e. how to best sharpen an image, what
unsharpness can be eliminated in post-processing)? Is there perhaps some
web page with details?
--
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
  #2  
Old September 13th 14, 08:48 AM posted to rec.photo.digital
Savageduck[_3_]
external usenet poster
 
Posts: 15,578
Default Lenses and sharpening

On 2014-09-13 07:23:17 +0000, Alfred Molon said:

Sometimes a soft lens can be very effectively compensated by some
unsharp mask in post processing and you get a sharp, natural looking
image.

But sometimes no matter how much sharpening you apply or what parameters
you choose, you get that unnatural, "sharpened" look.

It probably depends on the unsharpness of the lens, its (spatial)
frequency response or whether the sharpness is caused by the lens glass
itself (i.e. lens not being sharp enough), inaccurate focus or some
motion blur.

For instance I have a 70-300 lens which at the tele end generates a bit
soft images, which however respond well to unsharp masking in post-
processing. But that's not the case for the another lens I have (a mid-
range one).

Has somebody analysed this (i.e. how to best sharpen an image, what
unsharpness can be eliminated in post-processing)? Is there perhaps some
web page with details?



First are we talking sharpening in general, sharpening to overcome
softness due to exposure settings, or issues with a particular lens?

Next, if it is a particular lens which lens? If you are talking about
the 70-300mm, what brand and model, and mounted on which camera?

Is the softness you are experiencing over the entire image, or edge softness?

What post processing tools/software are you using?

Are these RAW image files or JPEG?

When in your workflow do you usually apply any particular sharpening method?

--
Regards,

Savageduck

  #3  
Old September 13th 14, 12:55 PM posted to rec.photo.digital
Floyd L. Davidson
external usenet poster
 
Posts: 5,138
Default Lenses and sharpening

Alfred Molon wrote:
Sometimes a soft lens can be very effectively compensated by some
unsharp mask in post processing and you get a sharp, natural looking
image.

But sometimes no matter how much sharpening you apply or what parameters
you choose, you get that unnatural, "sharpened" look.

It probably depends on the unsharpness of the lens, its (spatial)
frequency response or whether the sharpness is caused by the lens glass
itself (i.e. lens not being sharp enough), inaccurate focus or some
motion blur.

For instance I have a 70-300 lens which at the tele end generates a bit
soft images, which however respond well to unsharp masking in post-
processing. But that's not the case for the another lens I have (a mid-
range one).

Has somebody analysed this (i.e. how to best sharpen an image, what
unsharpness can be eliminated in post-processing)? Is there perhaps some
web page with details?


Sharpening up the focus can be done to a limited extent.
UnSharp Mask is probably the most limited of various
sharpening tools. Likewise any sort of "smart sharpen"
that tries to isolate tonal edges will be less useful.

A true (not what Adobe labels as HP) high pass sharpen
tool will be fairly good. The problem is that most
image editors do not let the user set all the
parameters, and often limit user configuration to just
an amount.

One better option might be wavelet sharpen.

But probably the most useful would be Richardson-Lucy
Deconvolutional sharpening. Using just standard default
filters (Gaussian and perhaps exponantial) for the point
spread function should work better than other sharpen
tools, but it would also be possible to develop a very
accurate point spread function for any given specific
lens (think of the Hubble Telescope), and that would be
very significantly better than other methods.

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)
  #4  
Old September 13th 14, 09:18 PM posted to rec.photo.digital
Alfred Molon[_4_]
external usenet poster
 
Posts: 2,193
Default Lenses and sharpening

In article [email protected], Savageduck
says...

First are we talking sharpening in general, sharpening to overcome
softness due to exposure settings, or issues with a particular lens?


Over- or underexposure do not cause softness. This can come from
incorrect focus, a soft lens or camera shake.

Next, if it is a particular lens which lens? If you are talking about
the 70-300mm, what brand and model, and mounted on which camera?

Is the softness you are experiencing over the entire image, or edge softness?

What post processing tools/software are you using?

Are these RAW image files or JPEG?

When in your workflow do you usually apply any particular sharpening method?


The files usually are RAW. I don't have ready made examples. It's just
something I have observed over time, that sometimes image softness can
be very effectively eliminated with some sharpening, sometimes not.
--
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
  #5  
Old September 13th 14, 09:23 PM posted to rec.photo.digital
Alfred Molon[_4_]
external usenet poster
 
Posts: 2,193
Default Lenses and sharpening

In article , Floyd L. Davidson says...

But probably the most useful would be Richardson-Lucy
Deconvolutional sharpening. Using just standard default
filters (Gaussian and perhaps exponantial) for the point
spread function should work better than other sharpen
tools, but it would also be possible to develop a very
accurate point spread function for any given specific
lens (think of the Hubble Telescope), and that would be
very significantly better than other methods.


If the softness is caused by a particular camera-lens combination, is
there a way to determine this point spread function with for instance
some calibration steps, and then apply the right sharpening/
deconvolution?

I'm even wondering if this point spread function could be determined
from an image (without any previous camera/lens calibration), so that
the image processing software can choose the right sharpening algorithm
and parameters.
--
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
  #6  
Old September 13th 14, 10:47 PM posted to rec.photo.digital
Floyd L. Davidson
external usenet poster
 
Posts: 5,138
Default Lenses and sharpening

Alfred Molon wrote:
In article , Floyd L. Davidson says...

But probably the most useful would be Richardson-Lucy
Deconvolutional sharpening. Using just standard default
filters (Gaussian and perhaps exponantial) for the point
spread function should work better than other sharpen
tools, but it would also be possible to develop a very
accurate point spread function for any given specific
lens (think of the Hubble Telescope), and that would be
very significantly better than other methods.


If the softness is caused by a particular camera-lens combination, is
there a way to determine this point spread function with for instance
some calibration steps, and then apply the right sharpening/
deconvolution?


Any good optical engineer could work it out, given the
right equipment and a fairly fat check.

That's not a likely route for any but the most serious and
well healed.

And in fact using a Gaussian spread will work rather well
for a slight defocus problem, for diffraction, and for
"haze" from atmosphere.

I don't know for sure, but seem to remember that there
is software available that will measure motion blur and
might be able to produce a custom point spread function
to counter it.

I'm even wondering if this point spread function could be determined
from an image (without any previous camera/lens calibration), so that
the image processing software can choose the right sharpening algorithm
and parameters.


Some aspects might be. To really do it right though
you'd need to have the lens on an optical bench, or have
some very specific design specifications.

But sharpening by inspection using a default Gaussian
blur for the point spread function does do a fairly good
job of sharpening. I'm sure you can use Google to find
software that will let you try it. GIMP can do it with
a GMIC plugin.

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)
  #7  
Old September 14th 14, 12:06 AM posted to rec.photo.digital
Kevin McMurtrie[_3_]
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Posts: 108
Default Lenses and sharpening

In article ,
Alfred Molon wrote:

Sometimes a soft lens can be very effectively compensated by some
unsharp mask in post processing and you get a sharp, natural looking
image.

But sometimes no matter how much sharpening you apply or what parameters
you choose, you get that unnatural, "sharpened" look.

It probably depends on the unsharpness of the lens, its (spatial)
frequency response or whether the sharpness is caused by the lens glass
itself (i.e. lens not being sharp enough), inaccurate focus or some
motion blur.

For instance I have a 70-300 lens which at the tele end generates a bit
soft images, which however respond well to unsharp masking in post-
processing. But that's not the case for the another lens I have (a mid-
range one).

Has somebody analysed this (i.e. how to best sharpen an image, what
unsharpness can be eliminated in post-processing)? Is there perhaps some
web page with details?


Defects in lenses rarely produce a Gaussian blur or haze that can be
corrected with an unsharp mask. It's a complex mess with too many
variables to compensate for.

It's better to buy a higher quality lens if you're spending lots of time
on correction. Some mid-range lenses can be nearly perfect within a
reduced range of aperture and focal length. Sharpness charts can help
you decide what works for you. Around f/2, stabilization becomes more
practical than a larger aperture for low light hand-held photography.

If you're talking about the Canon 70-300 DO IS USM, there's a magic
aperture somewhere near f/6. The next step is to apply a small amount
of a large diameter unsharp mask to remove the haze. Don't let the
camera use small apertures. 300m at f/40 takes a picture of the fresnel
lens :P

--
I will not see posts from astraweb, theremailer, dizum, or google
because they host Usenet flooders.
  #8  
Old September 14th 14, 12:13 AM posted to rec.photo.digital
Savageduck[_3_]
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Posts: 15,578
Default Lenses and sharpening

On 2014-09-13 20:18:05 +0000, Alfred Molon said:

In article [email protected], Savageduck
says...

First are we talking sharpening in general, sharpening to overcome
softness due to exposure settings, or issues with a particular lens?


Over- or underexposure do not cause softness.


Agreed. However, aperture setting can play a part, and shutter speed
can play a part when it comes to shake or motion blur.

This can come from incorrect focus, a soft lens or camera shake.


Characteristics of a particular lens exhibiting softness is one thing,
chronic OoF issues another. First eliminate situational, shooter error
for any particular images. If this is an issue unique to a particular
lens, it might be time to find out what others have experienced with
that lens/camera combination, and what if any solutions they were able
to reach. Who knows, perhaps a lens focus calibration is in order.

Camera shake is quite obvious is something else all together, and I
wouldn't describe that particular aberration as "softness". One of the
most common causes of shake beyond the shooter's ability to hold
steady, is gusty wind.

Depending on the tools you have handy for post, some camera shake can
be neutralized. In PS there is the *Shake Reduction* filter, which with
the right image can improve things, but it doesn't always do the trick,
and takes a little practice to get right. Other software might have
some equivalent motion blur correction ability.

Next, if it is a particular lens which lens? If you are talking about
the 70-300mm, what brand and model, and mounted on which camera?

Is the softness you are experiencing over the entire image, or edge softness?

What post processing tools/software are you using?

Are these RAW image files or JPEG?

When in your workflow do you usually apply any particular sharpening method?


The files usually are RAW. I don't have ready made examples. It's just
something I have observed over time, that sometimes image softness can
be very effectively eliminated with some sharpening, sometimes not.


....and what PP software, & what sharpening methods do you use?
I am not going to advocate one application, or method over the other, I
know what advice I can give with what I am familiar with in my workflow.

Also when there is no obvious OoF issue, and depending on the software
you are using, the softness issue can be ameliorated, or even taken
advantage of in post.

--
Regards,

Savageduck

  #9  
Old September 14th 14, 08:30 AM posted to rec.photo.digital
Alfred Molon[_4_]
external usenet poster
 
Posts: 2,193
Default Lenses and sharpening

In article [email protected], Savageduck
says...
...and what PP software, & what sharpening methods do you use?
I am not going to advocate one application, or method over the other, I
know what advice I can give with what I am familiar with in my workflow.


Isn't unsharp mask the same across all PP applications? I would have
thought it's an algorithm which is implemented in various PP
applications, or are there differences?
--
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
  #10  
Old September 14th 14, 08:33 AM posted to rec.photo.digital
Alfred Molon[_4_]
external usenet poster
 
Posts: 2,193
Default Lenses and sharpening

In article , Floyd L. Davidson says...
Any good optical engineer could work it out, given the
right equipment and a fairly fat check.

That's not a likely route for any but the most serious and
well healed.


I'm wondering if the lens manufacturer could measure the point spread
function for its lenses and provide this information to image processing
applications, so that these could calculate the optimal sharpening
function.

In other words, software would compensate (at least partially) for the
weaknesses of a lens, as it is being done with vignetting or geometric
distortions in cameras.
--
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
 




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