Monday, October 15, 2007

Smart Sharpening - Fixing focus issues the easy way

In the Forensic Photoshop work flow, the first step after acquiring the image is to address issues of focus. One of the easiest ways to deal with focus is with Adobe's deconvolution filter, also known as Smart Sharpen. Here is a quick overview of the settings:

Filter>Sharpen>Smart Sharpen

There are two ways of working with the Smart Sharpen interface, Basic and Advanced. The Advanced mode has the same settings as Basic and allows you to fade the effect in the shadows and/or highlights.

Amount: Like Unsharp Mask, a higher value increases the contrast between edge pixels, giving the appearance of greater sharpness.
Radius: How far out do you want to apply the effect? The greater the radius value, the wider the area that will be subject to an increase in contrast. Enter too large a number and you will have noticeable halos.
Remove: Offers a selection of three ways to find and minimize the blur, thus sharpening the image:
  1. Gaussian Blur - This option works like the Unsharp Mask filter and is the fastest.
  2. Lens Blur - This option does a great job looking for edges and detail and thus produces finer sharpening of detail.
  3. Motion Blur - Got camera or subject motion blur? This option looks for it and reduces the effect. Be sure to measure the angle of blur with the Measure Tool, if you plan to use the Motion Blur option. (Make note of the measured value in the Options bar before entering the Smart Sharpen interface, and then input it into the Angle control field).
More Accurate: Processes the file twice for better removal of blur and enhanced sharpness. Be warned, this option can double processing time.

From the Advanced Settings:
Fade Amount: This adjusts the amount of sharpening in the highlights and/or shadows. Fade it all the way (100%) to conceal the sharpening. No fade (0%) gives maximum sharpening. Think of it as a Blending Mode's opacity slider in reverse.
Tonal Width: This controls the range of tones that are modified by Smart Sharpening. The lower the setting the more subtle the result.
Radius: The slider works like Radius in Basic mode and controls the size of the area around each pixel that is used to determine whether a pixel is in the shadows or highlights.

Now that you've seen how each of the settings works, give it a try on your images. Input your images. Then correct the focus. Then look at contrast, lighting, and colour. Then deal with noise. Then sharpen edges and detail. Interpolate if necessary and add a final touch of sharpening before you print or archive.

There are some photographers who advise moving into LAB mode before using Smart Sharpen. I tend to agree, but with certain exceptions and it depends on the image. Mostly, I would convert to LAB mode during the final sharpening step, not necessarily at the focus correction step. Try it for yourself and see if you can tell the difference.

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