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Author Topic: Sharpening ... Not the Generally Accepted Way!  (Read 53592 times)

digitaldog

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #60 on: August 10, 2014, 05:05:20 pm »

Here is one page that shows several methods from one blurry image.
http://www.deconvolve.net/bialith/Research/BARclockblur.htm
Interesting and I'll dig into it, thanks.
So is this about making out of focuse images appear in focus?
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Deconvolution is a process designed to remove certain degradations from signals e.g. to remove blurring from a photograph that was originally taken with the wrong focus (or with camera shake).
« Last Edit: August 10, 2014, 05:08:14 pm by digitaldog »
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bjanes

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #61 on: August 10, 2014, 05:08:33 pm »

USM as it's done in Photoshop and elsewhere is 50 years old?

Maybe Eric and Bart can comment on the lack of control of PSFs.

Photoshop isn't 50 years old, but the unsharp filter is a digital implementation of the unsharp mask that has been used in the darkroom for quite some time.

Regards,

Bill
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digitaldog

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #62 on: August 10, 2014, 05:11:58 pm »

Photoshop isn't 50 years old, but the unsharp filter is a digital implementation of the unsharp mask that has been used in the darkroom for quite some time.
I'm aware of that Bill, I actually did USM in the analog darkroom as a photo assignment in school, long before Photoshop.
I was under the impression that there was some algorithm or process that Photoshop (perhaps other software) conducted and just named UnSharp Mask hence the question. Someone could build such an algorithm and call it USM or anything else, what similarity is there to the process we used in the analog darkroom if any? Or was the name just applied because in the old days of Photoshop, the name was given to give us old time analog darkroom users something we could understand?
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Fine_Art

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #63 on: August 10, 2014, 05:14:35 pm »

Interesting and I'll dig into it, thanks.
So is this about making out of focuse images appear in focus?

Im not going to get into a word play highjack. Out of focus is an extreme example. Any reason for capture sharpening is a reson to deconvolve. If you start with good tools/ technique your need for capture sharpening may be minimal.
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digitaldog

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #64 on: August 10, 2014, 05:19:23 pm »

Im not going to get into a word play highjack. Out of focus is an extreme example. Any reason for capture sharpening is a reson to deconvolve. If you start with good tools/ technique your need for capture sharpening may be minimal.
Not meant to be wordplay, the question is about capture sharpening which I'd expect would be done on images that are not out of focus ideally. A set of algorithm's or processes that can do what you illustrate with out of focus images would indeed be very useful, no argument. The question is about current tools used on images that are not out of focus but need some work to over come issues with digitizing the image in the first place. The statement made was: Chances are people using deconvolve methods can beat anything done in LR/ACR. If the image is out of focus or has camera shake, the examples you should would be impressive and useful. Does that mean other methods that don't make out of focus images in focus fail to work when the rubber hits the road and final output sharpening and a print is produced?
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Robert Ardill

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #65 on: August 10, 2014, 05:19:58 pm »

Sometimes Wikipedia puts things quite nicely:

"For image processing, deconvolution is the process of approximately inverting the process that caused an image to be blurred. Specifically, unsharp masking is a simple linear image operation—a convolution by a kernel that is the Dirac delta minus a gaussian blur kernel. Deconvolution, on the other hand, is generally considered an ill-posed inverse problem that is best solved by nonlinear approaches. While unsharp masking increases the apparent sharpness of an image in ignorance of the manner in which the image was acquired, deconvolution increases the apparent sharpness of an image, but based on information describing some of the likely origins of the distortions of the light path used in capturing the image; it may therefore sometimes be preferred, where the cost in preparation time and per-image computation time are offset by the increase in image clarity.

With deconvolution, "lost" image detail may be approximately recovered—although it generally is impossible to verify that any recovered detail is accurate. Statistically, some level of correspondence between the sharpened images and the actual scenes being imaged can be attained. If the scenes to be captured in the future are similar enough to validated image scenes, then one can assess the degree to which recovered detail may be accurate. The improvement to image quality is often attractive, since the same validation issues are present even for un-enhanced images.

For deconvolution to be effective, all variables in the image scene and capturing device need to be modeled, including aperture, focal length, distance to subject, lens, and media refractive indices and geometries. Applying deconvolution successfully to general-purpose camera images is usually not feasible, because the geometries of the scene are not set. However, deconvolution is applied in reality to microscopy and astronomical imaging, where the value of gained sharpness is high, imaging devices and the relative subject positions are both well defined, and the imaging devices would cost a great deal more to optimize to improve sharpness physically. In cases where a stable, well-defined aberration is present, such as the lens defect in early Hubble Space Telescope images, deconvolution is an especially effective technique."

Robert
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Mark D Segal

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #66 on: August 10, 2014, 05:20:56 pm »

Fair enough.

Here is one page that shows several methods from one blurry image.

http://www.deconvolve.net/bialith/Research/BARclockblur.htm

corrected typo.

Yes, that page shows what is typically the key strength of the deconvolution approach. It allows one to retrieve usable information from an apparently hopelessly blurred photograph. This is particularly useful in forensics and espionage. How good it is for fine art photography is another matter. Some years ago I tested deconvolution software on photographs that simply needed the usual kind of acutance improvement for the usual reasons and I found the results ugly. And I tried numerous settings to make it look as good as I could, but it wasn't very prospective. Now, maybe the software has improved a lot in the intervening period, but since then I haven't gone back to it because I haven't perceived any need to do so. Time is my scarcest resource, very valuable and how I use it therefore carefully selected.
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Mark D Segal (formerly MarkDS)
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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #67 on: August 10, 2014, 05:27:05 pm »

Yes, that page shows what is typically the key strength of the deconvolution approach. It allows one to retrieve usable information from an apparently hopelessly blurred photograph. This is particularly useful in forensics and espionage. How good it is for fine art photography is another matter. Some years ago I tested deconvolution software on photographs that simply needed the usual kind of acutance improvement for the usual reasons and I found the results ugly. And I tried numerous settings to make it look as good as I could, but it wasn't very prospective. Now, maybe the software has improved a lot in the intervening period, but since then I haven't gone back to it because I haven't perceived any need to do so. Time is my scarcest resource, very valuable and how I use it therefore carefully selected.

Everyone has to decide if a particular image is worth time.
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digitaldog

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #68 on: August 10, 2014, 05:30:49 pm »

Everyone has to decide if a particular image is worth time.
I supsect that is what Mark, myself and perhaps Robert would like to see. No question the examples you provided show a huge benefit working with actual out of focus images. Now how about those that are not so severely awful? In such a case, are the chances people using deconvolve methods can beat anything done in LR/ACR?
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Bart_van_der_Wolf

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #69 on: August 10, 2014, 05:34:21 pm »

Yes, exactly ... the problem is we don't currently have the tools to do that (perhaps some of them, but the overall problem is quite complex because there are many reasons for the loss of detail in the image, and these all need to be known for the image to be properly 'fixed' with deconvolution).  Also, I wonder ... and perhaps Bart could answer this ... whether or not a deconvolution function would be any more effective than an unsharp mask, carefully tuned, for blurring due to the AA filter.)

Hi Robert,

Yes, deconvolution is perfect for Capture sharpening, and it's also very good for restoration of some of the upsampling blur, and yes these can also be combined if one wants to avoid upsampling any artifacts. For workflows involving Photoshop, I can recommend FocusMagic. What my analysis has shown, Capture sharpening should be 'focused' at Aperture dictated blur (not image detail as suggested in 'Real world Image sharpening'). The amount of blur (in the plane of best focus) is largely Gaussian in nature, due the the combination of several blur sources (which tends to combine into a Gaussian distribution), and varies with aperture.

Resampling (up/down) also creates blur due to averaging of pixels.
 
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Weeelll ... is that entirely true?  Emphasizing edges (beyond compensation for ink bleed) will create an impression of sharpness - and that isn't strictly 'creative sharpening' ... although of course there's no reason why you couldn't call it that.

Pre-compensation for ink diffusion (also pretty Gausian looking), or raster dots/lines, or to compensate for the low resolution of most displays, are the main areas of attention, but one can also optimize local detail for viewing distance if that is is relatively fixed.

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There is no claim to fame at all here - as I've said, it's just a question: "Is a 2-step sharpening process always necessary, given our currently available technology?".  I hardly think I'm the first person to have suggested a one-pass sharpening!!  No doubt this is what everyone did before the 2 or 3 pass sharpening came into vogue.

In many cases a one step sharpening approach is very well possible, especially for large format output and if the Capture sharpening tools are limited in quality (no-deconvolution) with halo risk. For optimal one-step sharpening one may need to combine several Gaussian blur radii, and produce a combined deconvolution kernel, but a single deblur operation already goes a long way.

Cheers,
Bart
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Mark D Segal

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #70 on: August 10, 2014, 05:34:38 pm »

Sometimes Wikipedia puts things quite nicely:

Robert

Thank you for that Robert, and the bottom line one gets out of it is "horses for courses".

Very unclear to me that deconvolution tools are ideally suited to efficient and high quality workflows in "fine-art" photography. The onus is on those who propose them to demonstrate superiority in regard to both quality and efficiency. And while we are at it, let us not forget the need to define what we mean by "best" when we are talking about the quality of a sharpening outcome. Only when we agree on the criteria defining "best outcome" can we determine what is "best practice".
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Mark D Segal (formerly MarkDS)
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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #71 on: August 10, 2014, 05:41:04 pm »

I supsect that is what Mark, myself and perhaps Robert would like to see. No question the examples you provided show a huge benefit working with actual out of focus images. Now how about those that are not so severely awful? In such a case, are the chances people using deconvolve methods can beat anything done in LR/ACR?

When I do go to print I usually like to have lots of pixels in the file. With deconvolution I feel Bart's 3x upsample recommendation is workable to get fair detail, good for printing, out of the image pixels. Anyone who thinks they can get close to optimal results from a raw can throw out a challenge with the file. I have offered that before with raws for the standard Imaging Resource reviews which include many raw shots. I doubt anyone can get sharp 3x upsampled images with ACR/LR.

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Mark D Segal

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #72 on: August 10, 2014, 05:44:29 pm »

When I do go to print I usually like to have lots of pixels in the file. With deconvolution I feel Bart's 3x upsample recommendation is workable to get fair detail, good for printing, out of the image pixels. Anyone who thinks they can get close to optimal results from a raw can throw out a challenge with the file. I have offered that before with raws for the standard Imaging Resource reviews which include many raw shots. I doubt anyone can get sharp 3x upsampled images with ACR/LR.



You're the one throwing out the challenges and expressing various views about the purported superiority of one approach over the other. I suggested above that you demonstrate the validity of your hypotheses by posting the comparative results of your own research.
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Mark D Segal (formerly MarkDS)
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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #73 on: August 10, 2014, 05:47:10 pm »

Thank you for that Robert, and the bottom line one gets out of it is "horses for courses".

Very unclear to me that deconvolution tools are ideally suited to efficient and high quality workflows in "fine-art" photography. The onus is on those who propose them to demonstrate superiority in regard to both quality and efficiency. And while we are at it, let us not forget the need to define what we mean by "best" when we are talking about the quality of a sharpening outcome. Only when we agree on the criteria defining "best outcome" can we determine what is "best practice".

There is no need to reinvent the wheel.

http://www.clarkvision.com/articles/index.html#sharpening
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digitaldog

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #74 on: August 10, 2014, 05:48:00 pm »

When I do go to print I usually like to have lots of pixels in the file. With deconvolution I feel Bart's 3x upsample recommendation is workable to get fair detail, good for printing, out of the image pixels. Anyone who thinks they can get close to optimal results from a raw can throw out a challenge with the file. I have offered that before with raws for the standard Imaging Resource reviews which include many raw shots. I doubt anyone can get sharp 3x upsampled images with ACR/LR.
I don't know what Perfect Resize is supposed to be using but the last tests I did with it, Photoshop (even doing step interpolation), LR sizing up 250%, LR was the best of the lot based on a final print. And oh so much faster. Proper capture sharpening made the biggest differences in the results.
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bjanes

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #75 on: August 10, 2014, 05:54:32 pm »

I'm aware of that Bill, I actually did USM in the analog darkroom as a photo assignment in school, long before Photoshop.
I was under the impression that there was some algorithm or process that Photoshop (perhaps other software) conducted and just named UnSharp Mask hence the question. Someone could build such an algorithm and call it USM or anything else, what similarity is there to the process we used in the analog darkroom if any? Or was the name just applied because in the old days of Photoshop, the name was given to give us old time analog darkroom users something we could understand?

In both the darkroom unsharp masking and with digital unsharp masking, the same general principle is to blur the image and then subtract the blurred image from the original. This subtracts out the low frequencies. This is explained in a Wikipedia article and in a post on Cambridge in Color.

With the darkroom form, blur is introduced optically. With the digital unsharp mask, Gaussian blur may be used, so the digital process is not an exact duplication of the darkroom process, but the principles are similar. Doug Kerr expounds in greater detail on the matter.

Regards,

Bill
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Mark D Segal

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #76 on: August 10, 2014, 05:56:14 pm »

There is no need to reinvent the wheel.

http://www.clarkvision.com/articles/index.html#sharpening

What he has in that article isn't the wheel. There are better acutance-enhancing tools than Photoshop's USM, and some of the comparisons he shows even at that are awfully close, and probably indistinguishable at normal magnifications and viewing distances. I remain unconvinced. And yes Andrew, you're right: cost-effectiveness in terms of time versus practical outcomes is a real consideration.
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digitaldog

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #77 on: August 10, 2014, 06:00:04 pm »

In both the darkroom unsharp masking and with digital unsharp masking, the same general principle is to blur the image and then subtract the blurred image from the original.
OK, same general principle. But I suspect there are multiple products using the term and not producing the same results using the same original data. In fact I know that as I just applied USM in Graphic Converter then Photoshop using the same values and they are not the same! GP only has two of the three controls found in PS (Radius and Intensity which I suspect is akin to Amount).
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Fine_Art

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #78 on: August 10, 2014, 06:06:33 pm »

What he has in that article isn't the wheel. There are better acutance-enhancing tools than Photoshop's USM, and some of the comparisons he shows even at that are awfully close, and probably indistinguishable at normal magnifications and viewing distances. I remain unconvinced. And yes Andrew, you're right: cost-effectiveness in terms of time versus practical outcomes is a real consideration.

That is not an article, it is a series. If you go through it it shows a comparison of the PS smart sharpen with richardson-lucy here: http://www.clarkvision.com/articles/image-restoration2/index.html

There are already several deconvolution threads on the site so to me remaining unconvinced= remaining in the dark. Your choice.
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bjanes

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Re: Sharpening ... Not the Generally Accepted Way!
« Reply #79 on: August 10, 2014, 06:08:50 pm »

OK, same general principle. But I suspect there are multiple products using the term and not producing the same results using the same original data. In fact I know that as I just applied USM in Graphic Converter then Photoshop using the same values and they are not the same! GP only has two of the three controls found in PS (Radius and Intensity which I suspect is akin to Amount).

Yes, that is what Doug Kerr discusses in his article (if you take the time to read it).

Regards,

Bill
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