Sharpening ... Not the Generally Accepted Way!

[Robert Ardill]

Hi,

I'm posting this with some trepidation as I expect a lot of disagreement.  But here goes!

My understanding of the 3-step sharpening proposed by Shewe et al is: a. Capture Sharpening with an edge mask; b. Creative Sharpening to taste; c. Output Sharpening with no edge mask.

I would like to propose (no doubt others have before me, so perhaps I should say re-propose) an alternative, which I think has advantages.  And that is: a. Output Sharpen after any resizing, tonal/color adjustments etc; b. Creative Sharpening to taste.

I do have some empirical evidence to back this up, which I will come to in a moment.  But before that, my starting point is that sharpening should be minimized and that sharpening on top of sharpening should be avoided if at all possible.  The reason is simple: sharpening potentially damages the image.

So, on to the empirical side.

Here are the Photoshop layers I used to compare the different techniques:



1. The bottom layer is the unsharpened image upsized by 2x.
2. The 2nd layer up is with Capture Sharpening applied in Lightroom and then resized x2.  
3. The 3rd layer up is the resized image Capture Sharpened using Smart Sharpen and an edge mask.
4. The 4th layer up is a single sharpen for output from the original upsized image (layer 1).
5. The 5th layer up (top layer) is the upsized image, first with Capture Sharpen, then with Output Sharpen.

IMO the capture sharpen after resize (layer 3) is clearly better than layer 2.  So my first conclusion is Resize first, Capture sharpen second.

In the top layer, Layer 5, I have added output sharpening to the capture-sharpened image in Layer 3 (the output sharpen filter is above the capture sharpen filter, so it is applied after the capture sharpen). In the layer below that (layer 4) I have output sharpened the original upsized image (layer 1) in one go, as you can see.  For both layers 4 and 5 I have used the same edge mask as in Layer 3, but lightened a bit to let more fine detail through.

There was too much haloing in Layer 5, so I softened these using the Smart Sharpen fade shadows and highlights (quite a large amount 50% strength, 50% tonal width and radius 6 for both highlights and shadows).  I increased the amount of sharpening in Layer 4, not because I thought it needed it, but for direct comparison to Layer 5. So the amounts of output sharpening were different for Layer 4 and Layer 5 (more in Layer 4 as one would expect, to achieve a similar result to Layer 5).

My observation overall is that the same or a better result can be obtained with one-pass sharpening as with two and that it is better to resize, then sharpen, rather than capture sharpen, then resize.  The two-pass output sharpened image (Layer 5) still had ugly black lines, especially at the line between the mountains and the sky, whereas these were absent in the one-pass sharpening. These lines would certainly appear on a print and wouldn’t be acceptable to me.  To get rid of them would probably require a different sharpening algorithm (increasing the shadow fade didn’t help and reducing the radius wasn’t on as it was only at 2, which is probably the minimum for output sharpening at 300ppi).

Creative sharpening is possible with the output image (both for Layer 4 and Layer 5), simply by painting on the edge mask to add or remove sharpening.  

Whether or not there is more or less damage done using one approach over the other, from a workflow point of view the one-step sharpening is really simple and very easily automated.

This is a down-sampled crop of the test image I used (as you can see it has a good mix of very smooth skies and fine detail in the foreground):



BTW, this was the one-pass sharpened image from Layer 4, with the sharpening dialed down for web viewing. All I did was to down-size the image and adjust the Smart Sharpen filter.

It would be very interesting if someone else tried this out.  I’ve tried to be as objective as possible, but that isn’t so easy!

Robert

[Mark D Segal]

I would like to see you perform a comparison test of processing efficiency and results between all the stuff you propose here, and sharpening the same image - properly - using Photokit Sharpener Pro 2.

[Bart_van_der_Wolf]

Hi,

I'm posting this with some trepidation as I expect a lot of disagreement.  But here goes!

My understanding of the 3-step sharpening proposed by Shewe et al is: a. Capture Sharpening with an edge mask; b. Creative Sharpening to taste; c. Output Sharpening with no edge mask.

I would like to propose (no doubt others have before me, so perhaps I should say re-propose) an alternative, which I think has advantages.  And that is: a. Output Sharpen after any resizing, tonal/color adjustments etc; b. Creative Sharpening to taste.

Hi Robert,

I have indeed suggested in other posts that, when upsampling, there may be benefits to postpone Capture sharpening. Otherwise one runs the risk of magnifying any sharpening artifacts and only make them more visible by blowing them up to a larger size. Also with down-sampling, the addition of sharpening may increase the risk of creating aliasing artifacts. That's why I usually have sharpening layer in my files that can be switched off before resampling.

Creative sharpening on the other hand is IMHO a bit of a misnomer, although one can use sharpening tools to achieve the effect. It's more a detail enhancement/local contrast adjustment process than really sharpening. Therefore it can be done before upsampling, although its effect may change a bit with output size and viewing distance. It can be a very processor intensive operation, so large upsampled printfiles may take quite a while to be processed by the more advanced procedures.

Cheers,
Bart

[digitaldog]

Creative sharpening on the other hand is IMHO a bit of a misnomer, although one can use sharpening tools to achieve the effect. It's more a detail enhancement/local contrast adjustment process than really sharpening.

Sharpening can be a creative tool. Sometimes we want to make the image sharper than it really was, to tell a story, make a point, or emphasize an area of interest.
Nudging the image towards reasonable sharpness early on helps the editing process, and gives you a solid floor to stand on when it's time to make creative sharpening decisions.
Creative Sharpening. I don't tell people how to do art, so the only real guideline I can give here is to use common sense.

Bruce Fraser who I believe coined the term.
http://www.creativepro.com/article/out-of-gamut-thoughts-on-a-sharpening-workflow

[Bart_van_der_Wolf]

Bruce Fraser who I believe coined the term.
http://www.creativepro.com/article/out-of-gamut-thoughts-on-a-sharpening-workflow

Yes, he coined it 11 years ago if that article was the first time he mentioned it.

A lot has changed (for the better I might add), with regards to tools and technology. One only has to look at what e.g. Topaz Labs Detail can achieve, with preservation of color, and luminance targeted halo free adjustment of several sizes of detail (also deconvolution of the finest detail is possible). All optionally combined with very clever masking, and with separate controls for highlights, overall tones, and shadows.

I'm sure it would have been his wet dream, had it been available during his life.

I like the concept of Capture/Creative/Output sharpening (simple to remember and target a particular stage in the workflow), but sharpening (real resolution enhancement, not boosting acutance) is not necessarily the same as detail enhancement (it's only a very small subset of the possibilities).

Also, a program like Qimage offers a non-halo generating type of sharpening, called Deep-Focus sharpening (DFS). That's another thing Bruce could only dream of, given the trouble he took (had to take) to avoid halos that were inherent to the old USM methods dating back to the film days.

Cheers,
Bart

[Redcrown]

I second what Bart says. I think I used or tested every sharpening technique known in the past 10 years. But they are all obsolete for me with the adoption of Topaz Detail and Clarity. Somtimes in combination with complex luminosity masks or edge masks or manual masks, but not often.

[digitaldog]

Yes, he coined it 11 years ago if that article was the first time he mentioned it.

Then why the misnomer**? His description seems clear to me. You guys can use whatever products or techniques you wish, but how is what Bruce wrote to define Creative Sharpening, a misnomer? It is creative in it's direction, it makes the image appear sharper for that aim.

**a name that is wrong or not proper or appropriate

[Bart_van_der_Wolf]

Then why the misnomer**?

Hi Andrew,

I said 'a bit of a misnomer'. Sharpening is not the same as increasing acutance by boosting edge or local contrast. It only give an impression of sharpness by fooling the human visual system.

Only mathematical techniques like deconvolution can restore actual sharpness, both visual as well as objectively measurable. That's why NASA used a specific technique like Richardson-Lucy deconvolution to salvage the early Hubble space station's images ...
Techniques like Wavelet decomposition allow to address various larger detail levels, by boosting their weight, not by sharpening them.

Cheers,
Bart

[digitaldog]

Sharpening is not the same as increasing acutance by boosting edge or local contrast. It only give an impression of sharpness by fooling the human visual system.

So what term do you propose be used to replace sharpening behind capture, creative and output?

[Bart_van_der_Wolf]

So what term do you propose be used to replace sharpening behind capture, creative and output?

People can call it what they want, as long as they remember that (USM) 'sharpening' is but one of many (better) methods to visually enhance/subdue detail. They may call it Creative sharpening if they want, I do (but with a disclaimer).

Sharpening also suggests that increasing detail visibility is the only way to achieve one's creative vision. Reducing the visibility of structures can be equally important, to make the important detail stand out more. We also wouldn't necessarily call that blurring, it's more like de-emphasizing.

Noise reduction is similar, it's a targeted reduction of the visibility of noise (if possible without hurting resolution). That's also not blurring, although it can be used to crudely achieve the goal, sort of.

Cheers,
Bart

[Robert Ardill]

Having had a bit of a snooze after lunch and a glass of wine ... I am now ready to rejoin the battle!

I have to say that I think the term 'Creative Sharpening' is one of these things that has led many of us down the garden path.  It's like, "OK, to sharpen properly, you have to a) Capture Sharpen, b) Creative Sharpen, c) Output Sharpen, and if you forget b) well you haven't sharpened properly, have you?".  So many of us (me included) would capture sharpen in Lightroom, 'creative' sharpen in Photoshop (really adding more USM for no good reason) and then sharpen yet again for web or print.

The fact is that if we forget all about 'Creative Sharpening' and concentrate on the image, we will quite naturally do things like blurring parts of the image in order to make other parts stand out, we'll remove distracting detail, etc., just as we automatically do when we paint.  Having fine detail on the whole image is fine if we want to do a resolution test, but it's hardly going to make a beautiful picture, in most cases.  We'll also add contrast, which will make parts of the image stand out, adjust colors for the same reason ... all of which could come under the term 'Creative Sharpening' because they have the same objective of bring focus onto the important parts of the image ... but have nothing to do with sharpening.

This is not in any way to belittle Bruce or Jeff or Andrew or any of these guys' insights and wonderful work.  But things have moved on and it really isn't at all certain any more that it's advantageous to follow these 3 steps (or rather I should say these 2 steps, because creative sharpening really should at this point be taken out of the ladder).  The reason for my post was some testing I've done recently on QImage, and because of a comment by John here: http://www.luminous-landscape.com/forum/index.php?topic=92128.msg750983#msg750983.  It made me think, 'hmm, I've been doing this capture, output sharpening thing for years and it's been OK, but does it really make sense?', so I tried to remove capture sharpening and I was very happy to see that, actually, it is not a required step and that it may actually not be a good step at all ... and that's only using Smart Sharpen, which is really not a lot more than USM with a steering wheel.

I'm looking forward to doing some more testing with QImage and DFS ... which really does seem to be an amazing sharpening algorithm.  Bart keeps talking about deconvolution and it's interesting that no one seems to pick up on that (at least I haven't seen it, perhaps there's been lots of talk about it) - but it really is a key point in sharpening.  I don't know if the QImage Deep Focus Sharpening uses this sort of maths, but I have to say that one of the examples I posted seemed to be an almost perfect example: it restored a blurred square back to the original, almost perfectly.  If that is possible, then the notion of applying USM-type sharpening to 'repair' the blurring caused by lens, anti-aliasing filter etc., is almost criminal.

As for Topaz etc., ... seems I need to check out what's going on in the world these days!  For which I have to thank this forum.

Robert

[digitaldog]

People can call it what they want, as long as they remember that (USM) 'sharpening' is but one of many (better) methods to visually enhance/subdue detail.

If there's a misnomer, it's that term, USM which predates digital anything and was an analog darkroom process to produce the appearance of more sharpness. So I'd submit that Sharpening Photo's is the perception of the process onto that photo, not the specific process itself.

Sharpening is not the same as increasing acutance by boosting edge or local contrast.

Is sharpening an image the technique, be it analog or digital or the result of the technique as perceived by a viewer? I'd suggest it is the perceptual result which makes the image look sharper. At least considering the use of the term on images far before anyone was digitizing them.

[digitaldog]

We'll also add contrast, which will make parts of the image stand out, adjust colors for the same reason ... all of which could come under the term 'Creative Sharpening' because they have the same objective of bring focus onto the important parts of the image ... but have nothing to do with sharpening.

Does that selective and creative work make that area appear sharpner? Creative bluring (any blurning) is different?
Both effects have been available to affect photos’s long before anything photographic was digital.

[Robert Ardill]

Does that selective and creative work make that area appear sharpner? Creative bluring (any blurning) is different?
Both effects have been available to affect photos’s long before anything photographic was digital.

It could be that the term 'sharpening' is one that we should start to drop.  I'm more a painter than a photographer, to be honest, and as a painter I would never think in terms of 'sharpening' my painting.  What I do is to use various techniques (composition being one, of course) to bring attention to parts of the painting and away from others ... but mostly it's a question of removing detail rather than adding detail.  So in photography perhaps the term 'Creative Blurring' would be just as valid (more so, probably) than 'Creative Sharpening'.

I think that generally what I would think 'sharpening' means in photography is an attempt to restore lost detail.  So far, mostly, this has been achieved by a sort of flattery - it's a pretense only because, in fact, detail is lost rather than gained using techniques like USM.  However with newer techniques like deconvolution, it really is possible to restore apparently lost detail, if we know why the detail was lost (for example due to hand-shake).

So maybe we need to rethink our terminology.  It may lead to us becoming better photographers (and not just to 'sharper' photos).

Robert

[Mark D Segal]

Let us revert to fundamentals for a moment:

Two different concepts: focus and acutance.

Focus: A photo can be blurry from subject or camera movement, or because circles of confusion are visible due to D.O.F. limitations or poor focusing of the lens. These are focus problems. Deconvolution sharpening tools have been designed to recover image detail from such problems.
Acutance: the micro-ciontrast of lighter to darker edges between pixels. Acutance reduces as a result of digital image processing at the capture, rendering, editing and printing stages. Bruce Fraser et. al. analyzed all these issues and more in great depth and produced techniques and corresponding software for addressing them that hasn't been fundamentally improved upon since their latest version. For readers who want more background into this, Jeff Schewe's book on sharpening is the best and most comprehensive published resource I know to recommend.

This discussion and the one in the other thread about QImage isn't always clear about what concept is at play: the focus concept or the acutance concept. Most digital imaging most people do these days is about the latter. And it is partly a matter of taste, partly a matter of credibility. If I were doing micro-photography I may want more detail on paper than I see in reality. For routine photography, the most natural appearance of detail corresponds with how I see it in the scene. As I've mentioned elsewhere before, if a photograph is meant to be sharp, it should look sharp but not sharpened. That is a fine distinction which I believe Photokit Sharpener 2, and Lightroom/ACR handle admirably; different people prefer different vendors' software - that's par for the course, but again, let us relate our preferences correctly to the concept. Tools designed primarily for acutance enhancement won't necessarily handle out of focus issues so admirably, because they are not dedicated deconvolution tools.  I use the tools I use because the benefit:cost ratio is very high. I'm not a techno-masochist; I just want good, credible results in a time-efficient manner.

[Robert Ardill]

Let us revert to fundamentals for a moment:

Two different concepts: focus and acutance.

Focus: A photo can be blurry from subject or camera movement, or because circles of confusion are visible due to D.O.F. limitations or poor focusing of the lens. These are focus problems. Deconvolution sharpening tools have been designed to recover image detail from such problems.
Acutance: the micro-ciontrast of lighter to darker edges between pixels. Acutance reduces as a result of digital image processing at the capture, rendering, editing and printing stages. Bruce Fraser et. al. analyzed all these issues and more in great depth and produced techniques and corresponding software for addressing them that hasn't been fundamentally improved upon since their latest version. For readers who want more background into this, Jeff Schewe's book on sharpening is the best and most comprehensive published resource I know to recommend.

This discussion and the one in the other thread about QImage isn't always clear about what concept is at play: the focus concept or the acutance concept. Most digital imaging most people do these days is about the latter. And it is partly a matter of taste, partly a matter of credibility. If I were doing micro-photography I may want more detail on paper than I see in reality. For routine photography, the most natural appearance of detail corresponds with how I see it in the scene. As I've mentioned elsewhere before, if a photograph is meant to be sharp, it should look sharp but not sharpened. That is a fine distinction which I believe Photokit Sharpener 2, and Lightroom/ACR handle admirably; different people prefer different vendors' software - that's par for the course, but again, let us relate our preferences correctly to the concept. Tools designed primarily for acutance enhancement won't necessarily handle out of focus issues so admirably, because they are not dedicated deconvolution tools.  I use the tools I use because the benefit:cost ratio is very high. I'm not a techno-masochist; I just want good, credible results in a time-efficient manner.

Well Acutance would be a good (and correct term) to use instead of Sharpness in these discussions.  I'm not sure about Focus though ... there are other reasons for loss of detail, for example the anti-aliasing filter, sensor noise, the analog to digital conversion, the demosaicing algorithm, resizing, etc., some or all of which can be corrected, at least to some extent, with techniques like deconvolution (but as I'm not an imaging scientist I have to defer to you guys for advice and information here).

I'm a bit tested-out at this stage: could you tell me something about how Photokit Sharpener 2 works?  In your experience that is, not from the product marketing info.

Robert

[Mark D Segal]

there are other reasons for loss of detail, for example the anti-aliasing filter, sensor noise, the analog to digital conversion, the demosaicing algorithm, resizing, etc.,

I'm a bit tested-out at this stage: could you tell me something about how Photokit Sharpener 2 works?  In your experience that is, not from the product marketing info.

Robert

All those reasons are included in the wording I used above, ref "digital imaging process", and much but not necessarily all of it is acutance-related.

The information about Photokit Sharpener on the PixelGenius website is very reliable. If you want a proper understanding of the underling principles, as I said, nothing I know of beats the Schewe book. As for how well it works, Michael Reichmann reviewed it on this website when the product first appeared - you can locate that product review. It is accurate. I was using it from the time of that review until its principles were ported into Lightroom, where I use that same approach very successfully now. If you are asking me about my personal experience with it: highly recommended. But nothing beats testing it yourself. As we all know - in spades - different people have different taste in software. What floats my boat may not necessarily float yours', or for that matter Barts'. So I suggest once you have recovered from the present round of testing overload, give it a shot and see what you think.

[digitaldog]

It could be that the term 'sharpening' is one that we should start to drop.  I'm more a painter than a photographer, to be honest, and as a painter I would never think in terms of 'sharpening' my painting.

Sharpening is a term that dates back into the analog film days. I've made USM's in the analog darkroom as an assignment in photo school, long before the word Photoshop existed. We were taught why the appearance of sharpness changed (due to changes of edge contrast), much like we understood what a grade 1 paper would do for an image compared to a grade 4 and that apparent visual effect of sharpness. USM may have produced something vastly different from the digital terms used here to express sharpness, but the reason we made prints this way was for one reason; to make the image visually appear sharper.

If one believes that the result of sharpening makes the image appear sharper, then the term and Bruce's explanation of Creative Sharpening is not a misnomer even a little. However, if the method used is a consideration not the result, then Creative Sharpening I would agree is a bit of a misnomer.

To me, the differences of the look of the final result is key but I understand how some consider the route to that result important. USM in the darkroom made the image appear sharper and that's why we went through this agonizing slow process. FWIW, we were also taught how to build contast masks in a simialr fashion for printing Ciba. We understood this wasn't a process that had anything to do with sharpening or bluring, again focusing (no pun intended) on the results of the process on image contrast in a much different way.

[Robert Ardill]

The information about Photokit Sharpener on the PixelGenius website is very reliable. If you want a proper understanding of the underling principles, as I said, nothing I know of beats the Schewe book. As for how well it works, Michael Reichmann reviewed it on this website when the product first appeared - you can locate that product review. It is accurate. I was using it from the time of that review until its principles were ported into Lightroom, where I use that same approach very successfully now. If you are asking me about my personal experience with it: highly recommended. But nothing beats testing it yourself. As we all know - in spades - different people have different taste in software. What floats my boat may not necessarily float yours', or for that matter Barts'. So I suggest once you have recovered from the present round of testing overload, give it a shot and see what you think.

Actually, now that I've had a look at Photokit Sharpener (on the web, that is), I realize that I had the version 1 some quite long time ago.  If I remember correctly it essentially uses actions to create sharpening layers, using high pass filtering, USM (or Smart Sharpen, perhaps) ... in other words Photoshop filters ... and in addition adjusts the effect using advanced blending (blend underlying layer sort of thing), different blend modes etc., and uses edge masks.  All very good and with the advantage that the user can tune the effects by modifying layer opacity, and so on.

Then it works out things like sharpening levels required based on image resolution, printer type, paper type, image size etc. So if you're working with lots of different printer types, different media etc., it's a useful tool.

I worked on some sharpening tools like these with Uwe Steinmueller some years back ... but at the end of it I felt that understanding the basic techniques and using them directly is better (for me).  So unless there's something really special in Photokit Sharpener 2 (and Andrew or Jeff can surely enlighten me) I think I'll give it a pass.

Robert

[Mark D Segal]

Yeah  - what's special about it is ease of use and high quality results. I'm just sharing my experience - for readers to use or not as they see fit.