The Downsides to Sharpening Macro Photographs
The postproduction sharpening tool is one that can enhance or destroy the quality of a macro or close-up image, depending on how you use it. It works best when applied in moderation, with just enough of an effect to increase the appearance of sharp focus, without revealing itself too easily to viewers.
Some of the problems you face when using a sharpening filter can include:
Noise, which happens to be one of the easiest things to sharpen. That’s bad luck because it also is probably the last thing you want to sharpen. When noise is sharpened it becomes more evident in an image, especially in the shadow areas. Try adjusting the threshold when applying a sharpening filter to minimize its effect on the noise in your image.
A halo often becomes clear when you oversharpen an image or select too high a radius. This halo is a dead giveaway to viewers that an image was sharpened in postproduction. The trick to successful postproduction is to optimize an image without making the enhancements individually noticeable. Be sure to sharpen your images just enough so the halo isn’t visible from a normal viewing distance.
Color artifacts can sometimes appear after a sharpening mask has been applied. To correct this problem, you can select Edit→Fade Unsharp Mask, and then set the effect to Luminosity mode (this technique must be done immediately after the filter is applied).
Another option is to copy your image layer and apply the sharpening filter to the new layer. Then set that layer to Luminosity mode. This ensures while you work with the color of an image, the contrast stays the same.
The sharpening filter can sometimes roughen smooth areas. To keep this from happening you can set the threshold to keep those areas from being affected. Another option is to create a layer mask on the layer that you’re sharpening, and block the effect from the smooth areas entirely.