There’s an updated edition of the Real World Sharpening book co-authored by Jeff Schewe … on Amazon.com:
A summary of the concepts which are on Flickr.com, written by Godfrey DiGiorgi:
Sharpening should be looked upon as having three separate components, or phases, or contexts.
– Digital capture sensors typically have an antialiasing filter in front of the sensor which help to eliminate moire artifacts as edges come into conjunction at the resolution of the photosite array. That’s a complicated way to say that if you have a thin straight line and you rotate it on the sensor so that it is almost in alignment with a line of photosites, there will come a point where the thin straight line will randomly register on one side or the other of a boundary between photosites. The antialiasing filter blurs and widens the line to minimize the moire effect that this causes. In doing so, some resolution is lost.
Input sharpening is the operation of setting edge boundary contrasts to recover the perception of resolution to reduce this problem.
– In the course of rendering an image, there are times when it is valuable to decrease the perceptual sharpness in some areas relative to other areas, and increase the perceptual sharpness in some areas relative to other areas, in order to guide the viewers’ eyes to what and where you want their attention focused.
This is called Creative sharpening. It is implemented by selective application of sharpening and blurring operations on parts of the image.
– When outputting an image for display, either to a computer monitor or to a printer, you have to take into account the size (in pixels) and resolution of the device, and scale the image according to your presentation desires/needs. The process of scaling the image for the device will cause a certain amount of resolution loss since you are interpolating values from the original resolution to a lower resolution device.
Output sharpening is performed to correct for resolution losses and restore the perceptual sharpness so the image looks as you intend.
Lightroom 2 has the ability to perform input sharpening, creative sharpening and output sharpening.
– Input sharpening is performed in the Develop module using the tools in the Detail panel. It’s a very good application of the same basic algorithms posed by PhotoKit Sharpener with degree, radius, intensity and masking embedded.
– Creative sharpening capabilities are limited in Lightroom 2. They are performed using the selective area brush and are implemented by combinations of the clarity, contrast and sharpening sliders applied to areas of the image selectively, with or without masking. You can get a lot done with them, but they are nowhere near are sophisticated or as comprehensive as even the built-in creative sharpening facilities in Photoshop, never mind that dozen or three add-on plug-ins that do this sort of thing. Extensive creative sharpening needs constitute one of the primary reasons why I still, occasionally, have to Edit in Photoshop… with a tricky image.
– Output sharpening is performed in the Lightroom 2 Export dialog, in the Print module, in the Web module, and in the SlideShow module. Output sharpening is almost always very simple to do: given a finished image with a particular size and density, and given an output target of specified resolution and density, just so much edge enhancement needs to happen, very predictably, to recover the expected amount of resolution loss from scaling. The variability in the process has to do more with the nature of the scene … so low, medium and high values are applied. Lightroom 2 does a good job of scaling what those three settings mean in the context of the specified source and export destination.
When it comes to the practicum of my image processing work, I tend to use
– as little input sharpening as possible to recover from antialiased capture softness,
– as much or as little creative sharpening that the aesthetic needs of the image demand, and
– standard level output sharpening for most prints I make and web resolution images I render. I export with NO output sharpening when I’m going to add borders and other annotation details in Photoshop post Lightroom as I’ve embedded output sharpening into my actions that automate those operations already. And when I deliver images for clients to use for editing, I apply no output sharpening so that their production staff can apply the appropriate amount of sharpening required by the production and printing process they use.
I like photos that are reasonably sharp; so I import everything into Lightroom with landscape sharpening for VIEWING WHILE WORKING only. My last two steps are to reduce noise and then to sharpen. For noise reduction, I use 2:1 enlargement and then apply as little Color as possible and then as little Luminance as possible. I prefer to have a bit of noise and increased sharpness, rather than the other way around. Now, I’m ready to sharpen, and I back Amount, Radius, Detail and Masking entirely off to the left. Next, (still using 2:1 or 1:1) I add Amount until I just can see an increase in sharpness. Then I do the same with Radius and finally Detail. At that point, while holding down the Alt key, I adjust Masking to leave sharp (shown in white) only the areas that I want really sharp. I often end up with masking in the 50 to 90 range. I’ve been surprised at what high quality 16×20 prints I can get using that process, and I hardly ever sharpen in Photoshop or reduce noise in Noise Ninja any longer.