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04-10-2009, 12:10 PM   #1
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Should images be viewed at 100% when sharpening?

Everywhere i read about sharpening, everyone keeps saying that one has to view the image at 100% to get an acurate sharpening. I'm having problems doing this. To me, sharp means a nice clean line without jagged edges, etc. When viewing an image at 100% though, surely the image will look jagged, etc, despite being a sharp image as you are zooming inn so much. Wouldn't it make more sense to sharpen an image at 50%?

Being the paranoid bloke that I am, I'm very much in doubt about if my K200D focuses correctly. I tried photographing a page at a 45 degree angle. When viewing on screen it seems like the sharpes part of the image is about 2 lines bellow where I was focusing on all three pages that I shot, but I've also heard that these tests aren't very reliable. I've made a 100% (unless of course I've missunderstood the concept of what a 100% crop is and posted it bellow. I focused this man when I took the shot. Now I'm presuming that the slight bluriness on the line between him and the background is normal. I read somewhere that the camera blurs lines to prevent them from looking jagged. I applied some sharpening in Aperture as this shot was in RAW.

Now I'm hoping that everyone is going to tell me that I'm being paranoid and that this is how the edges are supposed to look when zoomed in to 100%.



04-10-2009, 12:26 PM   #2
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100% isnt zoomed in! ... its normal, every pixel is 1:1 on screen.

If you view at anything less your not seeing every pixel anymore so you cant make accurate judgement.

Image will not look jagged unless zoomed to an odd size... like 115% or 96%, and when you zoom in a lot its not going to be jagged but rather pixelated as you have multiple real pixels representing one picture pixel.

50% will look clean because its easily re sampled perfectly (even though you've not technically resized)

So to answer your question... yes.
04-10-2009, 12:36 PM   #3
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The correct amount of sharpening depends on the size you plan to view or print the image at. So you should apply sharpening at a size that corresponds to the size you intend to view/print the image at, and yes, that means different amounts of sharpening for differently sized versions of the image. Which is why they always say sharpening should be the *last* step in the workflow.

In the case of images that you plan to view on screen, that's easy enough - actually resize the image to the new dimensions, then sharpen. It's more complicated for images you intend to print. You probably want to leave the image at full resolution. You could then resize it *on screen* to resemble the final print size, but most programs when doing that will add some sharpening, so that can be deceptive. You should probably turn off any screen resize sharpening done by your display software. But the bigger issue is that what looks right on screen might not match what looks best printed, even if at the same physical size in inches. If you're at a point where you're noticing that effect and being concerned about it, then you already know more about it than I...
04-10-2009, 02:03 PM   #4
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And all I wanted was a calming hobby

I obviously have a lot to learn.

04-10-2009, 02:13 PM   #5
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QuoteOriginally posted by alehel Quote
Being the paranoid bloke that I am, I'm very much in doubt about if my K200D focuses correctly. I tried photographing a page at a 45 degree angle. When viewing on screen it seems like the sharpes part of the image is about 2 lines bellow where I was focusing on all three pages that I shot, but I've also heard that these tests aren't very reliable.
Definitely true if you're shooting an ordinary page of text. *You* might know which line of text you meant to focus on, but the camera can't read your mind. Just because the little square lights up on the right line is irrelevant - the actual AF sensor is *MUCH* taller than that, and could easily focus a line or two above or below.

QuoteQuote:
I've made a 100% (unless of course I've missunderstood the concept of what a 100% crop is and posted it bellow. I focused this man when I took the shot. Now I'm presuming that the slight bluriness on the line between him and the background is normal. I read somewhere that the camera blurs lines to prevent them from looking jagged.
Some amount of that kind of blurring of detail also happens as part of the process of saving in JPEG as opposed to a lossless format like TIFF. Not normally anything to be concerned about - those sorts of artifacts are only visible when viewed at close to 100% or on correspondingly large prints.

QuoteQuote:
Now I'm hoping that everyone is going to tell me that I'm being paranoid and that this is how the edges are supposed to look when zoomed in to 100%.
Looks like a pretty normal JPEG viewed at 100% to me.

Last edited by Marc Sabatella; 04-11-2009 at 09:16 AM.
04-10-2009, 06:03 PM   #6
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QuoteOriginally posted by alehel Quote
I tried photographing a page at a 45 degree angle. When viewing on screen it seems like the sharpes part of the image is about 2 lines bellow where I was focusing on all three pages that I shot
To expound on Marc's comments, the AF focusing area is a lot larger than most people assume. Try this test:

1) Put a black dot in the middle of a white sheet of paper.
2) Set your camera to focus using only the centre AF point.
3) Aim your camera at the paper so that it fills the entire frame, and try to achieve a focus lock on the black dot.

The camera can't focus on the white sheet, only on the black dot. If you repoint the camera so that the black dot is slightly off-centre (to the right/left and above/below the centre circle) and repeatedly half-press to try to get a focus lock, you can get a pretty good idea of exactly how large the AF sensor is. When I did this with my K100D Super I was able to get a focus lock in approximately the area shown below:



If you superimpose this on the lines of text you were shooting, I'd imagine that more than one line of text fell within the AF area. The camera can legitimately focus on ANYTHING within that area, whether it's what you WANT it to or not. So it's quite possible that the camera was focusing correctly, just not where you wanted it to.
04-10-2009, 06:37 PM   #7
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If you do not sharpen at 1:1, you run a huge risk of oversharpening. It is much better to undersharpen to control haloes, especially if using Unsharp Mask sharpening.

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04-11-2009, 12:20 AM   #8
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Well, thanks everyone. I learnt more reading the replies to my thread than I did browsing the web for two hours. Really apreciate the help.

Now I just have a small question about lenses. A lot of people talk about how a lens back or front focuses rather than the camera. Does this only apply to lenses that have built in focusing motors, or can this also be an issue where the lens is reliant on the camera's builtin focusing engine.

Incidently, when I sharpen my images, I do it in Apple Aperture which deals with the PEF file rather then a jpeg. As a matter of fact, I very rarely work with the jpeg, as I usually find that Aperture manages to make all the corrections I want. Aperture doesn't write changes directly to file, rather it saves changes in a sort of info file which tells the program what changes have been made. Every time it displays the image, it reads the file to find out how to display it. You can also chose to remove any changes, such as sharpening, or revert back to the original file. I love this way of working as it means I can make as many mistakes as I want, and still fall back to the original, alowing me to learn from my mistakes. Surely the rule about performing sharpening last doesn't apply to this kind of editing? Or am I wrong there as well?


Last edited by alehel; 04-11-2009 at 12:26 AM.
04-11-2009, 01:39 AM   #9
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Regarding sharpening, I think it might be best be done at the viewing enlargement.

Sharpening is an artificial contrast enhancement of the pixels surrounding an edge. Say a perfect image of an edge is a jump of brightness level from one pixel to the next. Sharpening typically enhances the contrast jump by adding to the brightness of the pixel on the light side of the jump and subtracting from the brightness at the dark side of the jump.



Now if the sharpened edge is viewed at a smaller magnification the added contrast enhancement will be decreased in proportion to the magnification change (because it'll be averaged over multiple adjacent pixels); for example if an image sharpened at 1:1 is viewed at 1:2 the sharpening brightness jumps will be reduced by 1/2 - hence the sharpening effect will be decreased.

Iowa Dave
04-11-2009, 01:39 AM   #10
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accidental entry

Iowa Dave

Last edited by newarts; 04-11-2009 at 05:48 AM.
04-11-2009, 06:57 AM   #11
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QuoteOriginally posted by Marc Sabatella Quote
The correct amount of sharpening depends on the size you plan to view or print the image at. So you should apply sharpening at a size that corresponds to the size you intend to view/print the image at, and yes, that means different amounts of sharpening for differently sized versions of the image. Which is why they always say sharpening should be the *last* step in the workflow.
Doh! "Light dawns over Marble Head!", as my sister would say. That means my whole approach to date has been fundamentally flawed! I guess that's what I get for diving into pp without any structured training but I hope you'll forgive a heart-felt "^%$#@!@%^!" ;~)

I'll certainly apply this insight going forward but it means that everything "on the shelf" needs to be re-worked--pretty much from scratch--if I'm going to print (which, fortunately, I don't do often.) Oh, well--I'll just make up cards that say, "Fine photography since April 11, 2009."

Thanks for getting that essential point through my thick skull, Marc.

Last edited by dadipentak; 04-11-2009 at 07:51 AM.
04-11-2009, 09:10 AM   #12
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QuoteOriginally posted by alehel Quote
Now I just have a small question about lenses. A lot of people talk about how a lens back or front focuses rather than the camera. Does this only apply to lenses that have built in focusing motors, or can this also be an issue where the lens is reliant on the camera's builtin focusing engine.
It can happen with any AF lens. But a good many FF/BF problems are caused by the *camera*, not the lens. I'd wager *most* are, based on my limited understanding of what can actually cause these problems. But as much as these issues get discussed, I'm not convinced anyone here - myself included - really understands the issues very well.
04-11-2009, 09:15 AM   #13
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QuoteOriginally posted by dadipentak Quote
Doh! "Light dawns over Marble Head!", as my sister would say. That means my whole approach to date has been fundamentally flawed!
I wouldn't go *that* far. As others have suggested, doing some sharpening at 100% never hurts, and that should be pretty safe to do early in the workflow. Like in your RAW processor, if you shoot RAW. Some call it "capture sharpening", and that's actually all I *ever* do except when making large prints. I simply don't care to spend the time sharpening after resizing.

QuoteQuote:
I'll certainly apply this insight going forward but it means that everything "on the shelf" needs to be re-worked--pretty much from scratch--if I'm going to print (which, fortunately, I don't do often.)
Realistically, the only time you're likely to really notice problems is if you've been doing sharpening on small-sized screen views but then trying printing larger - you'll see artifacts you had no idea you were creating.
04-11-2009, 09:28 AM   #14
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Thanks for the reassurance, Marc! ;~) But this does explain some of the variations in sharpness I've observed and puzzled over.
04-11-2009, 09:32 AM   #15
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QuoteOriginally posted by alehel Quote
Well, thanks everyone. I learnt more reading the replies to my thread than I did browsing the web for two hours. Really apreciate the help.

Now I just have a small question about lenses. A lot of people talk about how a lens back or front focuses rather than the camera. Does this only apply to lenses that have built in focusing motors, or can this also be an issue where the lens is reliant on the camera's builtin focusing engine.

Incidently, when I sharpen my images, I do it in Apple Aperture which deals with the PEF file rather then a jpeg. As a matter of fact, I very rarely work with the jpeg, as I usually find that Aperture manages to make all the corrections I want. Aperture doesn't write changes directly to file, rather it saves changes in a sort of info file which tells the program what changes have been made. Every time it displays the image, it reads the file to find out how to display it. You can also chose to remove any changes, such as sharpening, or revert back to the original file. I love this way of working as it means I can make as many mistakes as I want, and still fall back to the original, alowing me to learn from my mistakes. Surely the rule about performing sharpening last doesn't apply to this kind of editing? Or am I wrong there as well?
You are correct here (as far as I know)... In general, programs like Aperture or Lightroom are applying the sharpening last for you, so you don't need to worry about the order - at least for full size exports or prints.

I do know that lightroom 1.* has an error where it will produce hideous halos and artifacts in high contrast areas when exporting a pic at a reduced size (i.e. for web display etc...), but your're using Aperture, so hopefully they did a better job than the Adobe folks. BTW, for folks using Lightroom 1.4, you can use the LR/Mogrify plugin to do high quality size reduction and sharpening on export - I hightly recommend it over Lr's builtin export algorithm.
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