Monday, October 31, 2011
These Photoshop filters make images look sharper by controlling the contrast between neighboring pixel edges. The drawback in using these filters is that it is easy to over sharpen the images which create color halos (banding) around the sharpened pixels and results in making the images more out of focus. To avoid this pitfall you can use the High Pass filter or a none color channel in the Lab color mode.
Understanding the limitations of each sharpen filter is important before using it so that the correct one is used. Below is a description of the sharpening filters and links to videos demonstrating how to use them.
Filters - Sharpen, Sharpen Edges, Sharpen More, Unsharp Mask
The Sharpen, Sharpen Edges, Sharpen More filters do not allow you to specify the amount of correction. The Sharpen More filter applies a stronger sharpening effect than does the Sharpen filter. The Sharpen Edges filter sharpens only edges while preserving the overall smoothness of the image. These filters are found under the Filter / Sharpen menu.
The Unsharp Mask filter allows you to specify the amount of correction. It is used to adjust the contrast of edge detail and produce a lighter and darker line on each side of the edge. This process emphasizes the edge and creates the illusion of a sharper image. Note: Unsharp Mask filter has nothing to do with Photoshop masks and DOES sharpen images.
• Video on how to use the Sharpen, Sharpen Edges, Sharpen More, and the Unsharp Mask filters "Photoshop Tutorial - Basic Sharpening"
Filter - Smart Sharpen
The Smart Sharpen filter (available in version PS5 and maybe also in PS4) allow you to specify the amount of correction. It sharpens an image by letting you set the sharpening algorithm or control the amount of sharpening that occurs in shadows and highlights. Adobe Photoshop recommends that this is the way to sharpen an image if you do not have a particular sharpening filter in mind. This filter is found under the Filter / Sharpen menu.
• Video on how to use the Smart Sharpen filter "Photoshop Tutorial - Smart Sharpening"
Filter - High Pass
High Pass filter allows you to specify the amount of correction. It retains edge details in the specified radius where sharp color transitions occur and suppresses the rest of the image. Note: A radius of 0.1 pixel keeps only edge pixels. The filter removes low-frequency detail from an image and has an effect opposite to that of the Gaussian Blur filter. This filter is found under the Filter / Other menu.
• Video on how to use the High Pass filter "Photoshop Video Tutorial - High Pass Sharpening"
Sharpening in Lab Color Space
If an image is sharpened in the L "color" channel of the Lab color space (L=lightness; a = the color green to magenta; b = the color blue to yellow) instead of the RGB color space (red, green, blue), color halos around the sharpened pixels are avoided. Below are videos showing two methods on using Lab color space to sharpen images.
• Videos sharpening an image by using an edge mask in Lab color space.
The first video of two "Photoshop Tutorial: Sharpening with LAB 1/2" And the second video of two "Photoshop Tutorial: Sharpening with LAB 2/2"
• Video sharpening an image by using several layers and masks in Lab color space. Note: This video is a little confusing and the presenter used a few four-letter words but I decided to include it in this article because the technique may be useful in sharpening some images.
"Lab Sharpening in Photoshop"
It is trial and error in choosing which sharpening filter to use on images because each image may be out of focus for a different reason. When using one, I usually first apply the Sharpen filter to the image because it is fast and one of easiest to use. But I enlarge the image to 200 percent to make sure that there are no halo effects and the resolution of the image is improved. If I am not satisfied I then use the Smart Sharpen filter and if still not satisfied I use the Lab Color technique with the Smart Sharpen filter.
Note: I cheated when showing the out of focus example at the top of this article. I blurred an in-focus image with a Photoshop Gaussian blur filter to illustrate that Photoshop can sharpen images. The extensive amount of blurring I made to the image may not show on your monitor. There is a limit on how much the sharpening filters can sharpen out-of-focus images and the example image may be too blurred to be able to recover the sharpness of the original image by using Photoshop sharpening filters.
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