Friday, August 10, 2012

All About Image Sharpening—08/13/12

Patti Thompson Published in Tip Of The Week
All About Image Sharpening—08/13/12
This Article Features Photo Zoom

Digital Photo Tip Of The Week
No Sharpening
Digital image files are sharp, but those image files can—and should—be made to appear even sharper. RAW shooters have to apply sharpness adjustments to make their RAW images look their best, while JPEG captures have some level of in-camera sharpening automatically applied. In either case, additional sharpening is usually beneficial once you've got your digital image files into your computer. You can do your sharpening during RAW conversion and/or at the end of the editing process.

Just to be clear, sharpening isn't a replacement for making a sharp, focused image file. Digital image sharpening simply enhances edges to make images appear even sharper. You can control whether you adjust major edges or fine little edges—that's the art of sharpening. However you choose to do it, be forewarned: although sharpening is crucial, oversharpening is deadly. Be sure to use your tools wisely to maximize sharpness without creating the jaggy edges, increased noise and general ugliness that come from an oversharpened image.

In Lightroom (as well as Adobe Camera RAW) sharpening is fairly refined. It's my favorite place to sharpen images as I'm able to apply the appropriate sharpness and work with sharpening presets based on how an image will eventually be displayed—matte or glossy paper, or on screen or in print, for instance. The best part about sharpening during the RAW conversion is that the software actually helps you out by waiting and applying the sharpening to the file on output at the optimum stage. So you don't have to be concerned so much about when you sharpen, and you can concentrate more on how you sharpen—which, by the way, is accomplished by adjusting Amount, Radius and Detail sliders in the Sharpening area of the Detail pane. That is found in Lightroom's Develop Module. Amount affects the overall intensity of the sharpening, while Radius impacts the size of the sharpened edges. Detail amplifies finer, detailed edges within the scene. (Keep this slider low to minimize oversharpening of fine textures.) There's a fourth slider in Lightroom as well, and that's the Masking control. Set to zero by default, sharpening will be applied evenly across the image. Increasing this slider restricts sharpening to only the strongest, boldest edges in a scene. If you want to see exactly which edges will be sharpened, hold down the Alt/Option key while sliding the Masking slider. White areas will be sharpened, black areas will not. This is a great way to be sure you're applying sharpening only where you want it. And the Alt/Option trick works with every slider to let you see exactly what pixels you're altering.

Digital Photo Tip Of The Week
If you're a JPEG shooter, or if you'd simply take the "old school" approach of applying your sharpening as the last step prior to output of your finished image files from Photoshop, then you may want to investigate the oldest of sharpening tools, the Unsharp Mask filter. With a name that sounds like it's doing the exact opposite of what you're trying to accomplish, Unsharp Mask actually works the same way as a traditional darkroom technique—both are designed to make an image appear sharper than it actually is. It's applied as the last step in the editing process because you want to know how large the image file will be (sized for the screen, for instance, or for high-res printing) so that you can match the appropriate sharpness to the file. Since you'll see oversharpening with your own eyes, it's important to apply sharpening to a file that consists of the actual pixels of the finished image. Much like Lightroom, the sliders here consist of Amount (the intensity of the sharpening), Radius (how many pixels the sharpening will extend from a given edge) and Threshold (which works like Masking in Lightroom to determine whether you're applying sharpening evenly across an image or applying it only to the strongest edges—a great way to minimize noise).

Smart Sharpening hasn't been around quite as long as Unsharp Masking, but it's an equally beloved sharpening technique thanks to its variety of different sharpening approaches. With Radius and Amount controls that work much the same way as those sliders in the Unsharp Mask filter, Smart Sharpen does not offer a Threshold/Masking control. That means that if you've got a noisy image and you're concerned about amplifying noise, you may be better served by another approach. Instead Smart Sharpen offers your choice of which sharpening algorithm to use. Gaussian Blur behaves just like Unsharp Mask, while Lens Blur and Motion Blur are designed to minimize those respective causes of blurry images. The Shadow and Highlight tabs allow you to control how much sharpening occurs in, you guessed it, the shadows and highlight areas of the image. When sharpening halos get too strong and distracting, this control is a great way to mitigate the problem and prevent oversharpening.

Digital Photo Tip Of The Week
Over Sharpened
Whichever approach to sharpening you take, how do you know when you've gone far enough? If you've overdone it and created an artificially oversharp image you'll find that some of the primary edges in your scene—particularly those that separate areas of shadows from areas of highlights—will have distinctive and distracting "halos" of sharpness around them. The problem is that this oversharpness simply doesn't look realistic, and it can in fact be quite distracting if you're trying to create a realistic image. To take it down you can scale back the Amount, Radius or Threshold/Masking sliders in any of these sharpening tools. In order to maintain overall sharpness, keep the Threshold/Masking slider lower while you scale back Radius and Amount. If you'd like only certain areas to be very sharp, you can raise the Radius and Amount, as well as the Threshold/Masking slider to apply a stronger sharpening to only the boldest edges in the scene. However you do it, the important thing is that you actually do it. Make sharpening a standard part of your digital workflow.
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