Orquid "Phoenix"

Orquid "Phoenix"

by ceinmart

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I've seen a number of people recommend that you apply sharpening as the last step in post-processing, and some seem to imply you should always do that.

Why? I tend to discard pictures that either are not tack sharp at the focus point, or at least good enough that I don't mind. If I think the result looks good enough, even at 100%, why would I want to apply sharpening, and why should it be the last step performed?

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The last post-processing step should be asking yourself what you could have done better while taking the picture :) –  Itai Mar 4 '11 at 17:00
5  
Actually, that's what I ask myself both while taking the picture, and upon importing the pictures from the camera. I still take more shots than I probably need to, but I'm taking much more time now to review and delete photos in the camera on the spot. I don't post-process to rescue photos, I post-process to bring out the best. I think that's an important mind set when approaching the photo editing tools. –  Kim Burgaard Mar 4 '11 at 17:54
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4 Answers

up vote 25 down vote accepted

First of all, sharpening isn't (at least primarily) to compensate for pictures that weren't sharp -- it's primarily to reverse (or least ameliorate) the effects of interpolation that's inherent in converting the data from a typical Bayer-pattern sensor into a recognizable image.

There's also (at least typically) interpolation done when you resize an image. To compensate for that interpolation, you need to do the sharpening after the interpolation -- but you want to keep the image full size for as much post-processing a possible to maintain maximum quality in your editing. Therefore, you want to do all the other editing, then size the picture for the target, then do a final sharpening step to compensate for the interpolation in the sizing.

You might also want to read Patrick Lavioe's paper on sharpening in three steps.

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That's a great article... thanks! –  D. Lambert Mar 4 '11 at 16:45
1  
That article is a really good resource to have. Thank you. –  Vian Esterhuizen Mar 4 '11 at 20:58
    
Thanks! The article was very useful. I've been doing the capture and creative sharpening steps for some time now, and it makes sense to me when he says the final sharpening is less important when viewing the final result on a monitor. I rarely make prints of my photos –  Kim Burgaard Mar 5 '11 at 18:14
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Two reasons spring to mind:

  • If you do any cloning / comping / resizing / rotation these can all reduce sharpness so you should leave sharpening 'till after all these other steps have been performed (which is usually the end of the post processing process).

  • Your sharpening method / amount ought to depend on the destination media. Print work requires different sharpening than web output. For this reason I save my images unsharpened, and then sharpen for the specific destination as necessary. Images can also take up more space after sharpening so this is another reason not to sharpen until you have to.

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Another reason why not to sharpen at the very beginning already is: The impression of sharpness also depends on the viewing distance. If you sharpen an image at full resolution and then scale it down to 1/4 of the resolution, e.g. for the web, then the effect of sharpening will hardly be visible anymore. For example, you have pixels with the following values:

15 35
15 35

which might look like this after sharpening (the local contrast increases):

5 45
5 45

Then you scale it down to half the size, which would result in a single pixel with the value

25

(mean of the above). This is the same result you get with the unsharpened image. The point is, you also get a «downscaled» version of your image when watching it from greater distance (here's the link now :)). If the image is printed with 600 dpi, but my eye can only resolve 150 dpi from the position I watch it, then it can be sharpened stronger.

Also, sharpening is always a «lossy» operation, i.e. you try to guess what the original image looked like without really knowing it. And finally, sharpening can increase noise and compression artifacts, and it's usually a good idea to postpone all kind of quality loss as far as possible :)

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It depends

  • Sharpening removes detail (discards information), so if your editing is destructive, any editing done after the sharpening would have less information to work with than if it were done before the sharpening. If your editing is non-destructive then I'm not so sure. (I'm sure others can chip in here.)

  • Sharpening is the only (? I can't think of any others ?) edit which needs to be done differently depending on the target medium. E.g. you would sharpen a 20"x10" print differently from a 640x480 pixel image for a web page.

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If the editing is non-destructive, it probably still follows the order of operations you've given. (Otherwise, the results would be unpredictable.) –  mattdm Mar 4 '11 at 17:16
    
I would say that a lot of retouching also depends on the target medium. If you're going to size it down considerably, you don't need to be pixel-perfect. –  mattdm Mar 4 '11 at 17:17
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