The Fine USM Sharpen/Deblur .8bf Plugin
Fine USM Sharpen/Deblur gives you full control over the unsharp masking and deconvolution processes, including luminosity mode, halo elimination, very high amounts, edge masking, and blend ranges.
(The screenshot above was resized, but the preview inside it was copied and pasted from the actual sharpened image. Original was 7370 × 4916, unsharpened raw. Pine needles, in case you have never tried it, are very hard to sharpen without creating halos or other artifacts.)
• For unsharp mask sharpening, the Radius setting is generally small, and dependent on the resolution of the output medium. Typical values are 0.6 pixels for a 96 ppi screen, and 2 pixels for a 300 ppi print. Larger radii may be used for detail enhancement.
• The Amount setting for sharpening is generally large, sometimes several hundred percent. Values are chosen based on factors such as the sharpness of the original and the type of detail being sharpened.
• Dark/Light Mixer works as follows: the central position (zero) displays the processed image; the far left is like Darken blend mode, and the far right is like Lighten. This is used to adjust the balance of light and dark halos in the processed image. As light halos are generally more objectionable, a good default setting is about -70 for USM, possibly less for deblurring.
• Deblur is a simple deconvolution sharpening. This may be preferable to USM if all that is needed is a small amount of capture sharpening, or to “finish off” the image after a large amount of USM after resizing.
• The Radius setting is not quite as constrained as it is in USM; start with 2 pixels or so.
• When increasing the number of iterations, reduce the amount proportionately. A high number of iterations has a smoothing effect.
• Note that deblurring takes much longer than unsharp masking, especially at high radii.
• The edge mask may be used to sharpen edges and high-contrast areas only. Blur it with Radius, and adjust it with the Intensity and Level sliders. Its appearance is dependent on the size and content of the preview; it is best to view it at 100%. The processed image will use the same mask as the preview.
• Threshold determines the minimum lightness difference at which sharpening will be applied. It may be used to prevent the sharpening of noise or smooth surfaces. (Edge masking may be more effective.)
• Color controls how much of the processed color components are included in the final image. This is generally kept at zero (Luminosity blend mode) to prevent color fringes and the enhancement of color noise. It also lets the plugin run faster.
• Raise the lower black slider in Blend Ranges to gradually fade the sharpening effect in the shadows; lower the upper white slider to similarly fade the highlights.
• Dark and Light Intensity control how much of the original image is used in the blend ranges.
Presets include JPG Capture (screen), RAW Capture (screen), Reduce (screen), Enlarge (screen), Print 300 ppi, and Print 600 ppi. The settings are ballpark figures; one size never fits all. When printing, for example, if your workflow starts with capture sharpening then processing the full-sized image, you must take into account whether the image is resized before printing; if so, it will need more sharpening. Another option may be to pre-sharpen for the screen after resizing, then to sharpen for printing; this is probably not necessary.
Now that you have full control over the sharpening process, consider bilinear interpolation for halo-free image reduction. For enlarging, bicubic smoother and Mitchell-Netravali preserve detail better, and halos are less of an issue in general.
What about high-pass sharpening? At this scale, high-pass and USM sharpening are virtually identical. The differences are subtle, mostly the result of the choice of blend modes used to generate the high-pass image, and can be overcome by adjusting the sharpening amount. Unsharp masking is as good or better than any of the high-pass modes, and sometimes seems to preserve a little more shadow detail.
The plugin works with 8- or 16-bit RGB and grayscale images.
Download the zipped file, then copy FineUSMSharpen.8bf into your plugins folder. It will appear under “RC Filters.”
FineUSMSharpen_x64.zip version 1.110, 309 KB, 64-bit applications. It works for me in Photoshop CS5 and PhotoLine 20, Windows 7.
FineUSMSharpen.zip version 1.110, 304 KB, 32-bit applications, Windows 32 or 64 bit. It works for me in IrfanView 4, Windows 7. | source code
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© 2015 by Russell Cottrell; released under the
GNU General Public License.