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Lenses and sharpening



 
 
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  #11  
Old September 14th 14, 10:06 PM posted to rec.photo.digital
Eric Stevens
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Posts: 12,469
Default Lenses and sharpening

On Sun, 14 Sep 2014 09:33:29 +0200, Alfred Molon
wrote:

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.


I suspect that DxO does something like this: otherwise they could
operate ytheir 'Lens Sharpness' control of which they say:

"Lens softness compensates for the difference in sharpness between
the the center of the image, which is always better, and the edges,
where it is softer".
--

Regards,

Eric Stevens
  #12  
Old September 15th 14, 03:07 AM posted to rec.photo.digital
Eric Stevens
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Posts: 12,469
Default Lenses and sharpening

On Mon, 15 Sep 2014 09:06:44 +1200, Eric Stevens
wrote:

On Sun, 14 Sep 2014 09:33:29 +0200, Alfred Molon
wrote:

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.


I suspect that DxO does something like this: otherwise they could
operate ytheir 'Lens Sharpness' control of which they say:

"Lens softness compensates for the difference in sharpness between
the the center of the image, which is always better, and the edges,
where it is softer".


Let's try that again:

I suspect that DxO does something like this: otherwise they could not
operate their 'Lens Sharpness' control of which they say:

"Lens softness compensates for the difference in sharpness between
the the center of the image, which is always better, and the edges,
where it is softer".
--

Regards,

Eric Stevens
  #13  
Old September 15th 14, 05:13 AM posted to rec.photo.digital
Kevin McMurtrie[_3_]
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Posts: 108
Default Lenses and sharpening

In article ,
Alfred Molon wrote:

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?


The digital form of unsharp mask is the inverse of a blur. There's both
a frequency (diameter) and an intensity.

The fancier sharpening tools analyze an image and adapt the sharpening
to different types of blur in the image. This handles minor focus
problems, simple motion blur, and some of the radial blurring found in
cheap lenses.


The super-fancy tools will trace camera shake and estimate a corrected
image.

--
I will not see posts from astraweb, theremailer, dizum, or google
because they host Usenet flooders.
  #14  
Old September 15th 14, 06:31 AM posted to rec.photo.digital
Floyd L. Davidson
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Posts: 5,138
Default Lenses and sharpening

Kevin McMurtrie wrote:
In article ,
Alfred Molon wrote:

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?


The digital form of unsharp mask is the inverse of a blur. There's both
a frequency (diameter) and an intensity.


Not the case. It is the high pass sharpen tool that is the inverse of
blur. They can use the exact same algorithm with different parameters.
Using one and then the other virtually reverses the results.

UnSharpMask is not reversible.

The fancier sharpening tools analyze an image and adapt the sharpening
to different types of blur in the image. This handles minor focus
problems, simple motion blur, and some of the radial blurring found in
cheap lenses.

The super-fancy tools will trace camera shake and estimate a corrected
image.


--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)
  #15  
Old September 15th 14, 06:59 AM posted to rec.photo.digital
nospam
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Posts: 22,123
Default Lenses and sharpening

In article , Floyd L. Davidson
wrote:

UnSharpMask is not reversible.


it is with a non-destructive workflow.
  #16  
Old September 15th 14, 07:11 AM posted to rec.photo.digital
Alfred Molon[_4_]
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Posts: 2,195
Default Lenses and sharpening

In article , Kevin
McMurtrie says...
The super-fancy tools will trace camera shake and estimate a corrected
image.


Which would these be?
--
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
  #17  
Old September 15th 14, 08:12 AM posted to rec.photo.digital
Martin Brown
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Posts: 821
Default Lenses and sharpening

On 13/09/2014 08:23, 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.


For this to work well some very restrictive conditions have to be met -
notably that the entire image is uniformly blurred by a symmetrical and
spatially invariant point spread function (or one which varies slightly
and in a very predictable way with distance from the optic axis).

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


Anywhere that was already sharper to begin with than the presumed blur
will end up looking unnatural with ringing artefacts around it.

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.


You can only take out motion blur by modelling it. It can be done for a
price provided there is something in the image to play guess the
blurring function from. Used in car number plate recognition sometimes.

http://www.maxent.co.uk/example_1.htm

"Blind" deconvolution can also be done on larger images provided that
the blurring function is pretty much the same over the entire image.

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).


A lens which scatters a bit of light into a halo around everything migth
well tune up OK with a bit of unsharp masking.

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?

Astronomers have the most detailed instructions on how to deconvolve
images to obtain the maximum information about the night sky from finite
sized and imperfect instruments. They have one big advantage over
conventional photography in that their targets are all at infinity.

A rough rule of thumb is that at the highest signal to noise you can get
3x the spatial resolution on the highlights and brign the noise under
better control in the mid range. The price you pay is some unfamiliar
artefacts in the image which can be a nuisance in medical diagnostics
where practitioners are very familiar with the quirks of the standard
linear inverse methods for image reconstruction.

Depth of field issues make life very difficult for normal photography.

--
Regards,
Martin Brown
  #18  
Old September 15th 14, 11:32 AM posted to rec.photo.digital
Martin Brown
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Posts: 821
Default Lenses and sharpening

On 14/09/2014 08:30, Alfred Molon wrote:
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?


Unsharp mask historically was implemented by physical means to allow
very high contrast images to be more satisfactorily be represented on
printed media. It got adopted by David Mailn of the AAT to bring out
faint low contrast details in nebulae that would otherwise be invisible.

http://en.wikipedia.org/wiki/David_Malin

And from there it entered mainstream digital image processing.

It was in use for advertising purposes for quite a while prior to that.

The details of most algorithms are roughly similar but how they handle
underflow and overflow of pixel values may vary with implementation.

--
Regards,
Martin Brown
  #19  
Old September 15th 14, 05:39 PM posted to rec.photo.digital
Floyd L. Davidson
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Posts: 5,138
Default Lenses and sharpening

nospam wrote:
In article , Floyd L. Davidson
wrote:

UnSharpMask is not reversible.


it is with a non-destructive workflow.


I'm sorry that you don't understand the meaning of that.

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)
  #20  
Old September 15th 14, 05:53 PM posted to rec.photo.digital
nospam
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Posts: 22,123
Default Lenses and sharpening

In article , Floyd L. Davidson
wrote:

UnSharpMask is not reversible.


it is with a non-destructive workflow.


I'm sorry that you don't understand the meaning of that.


i absolutely do know the meaning, since it's all i use.

it's you who doesn't understand what a non-destructive workflow means
and as a result, says stupid **** like what you just did.

with a non-destructive workflow, unsharp mask (or anything else for
that matter) can be altered or removed after the fact. that's why it's
called a non-destructive workflow.
 




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