Using the High Pass Filter to Sharpen Images
Have you seen a sharp, clear photo taken by a high-end lens and thought how much better your photography would be with one of those. Well, believe me, I do love L Series Lenses for my Canon, but the fact is, rather than spending five or six times the price for a higher end lens, you can get a similar effect in Photoshop or Photoshop Elements that will sharpen your images well enough until you save for that special lens.
Actually Photoshop has a number of ways to add sharpening to an image. We will talk about three and leave the others for you to experiment. Since every photograph to some extent is different, I will provide you with general information, with the understanding that some experimentation might be needed to get it right. Visual analysis of each image is a far better method than following presets or formulas. Since I am using Photoshop CS6, I will discuss the features available in that program. Regardless your version, you will have these features, you just may need to look for them.
The first method and one I seldom use is the Unsharp Mask method of sharpening. If you click on filters in the main menu, the dropdown box will have a submenu for sharpening. Clicking on that will provide another dropdown and in CS6 the Unsharp mask filter is at the bottom. Clicking on this will bring up the Unsharp Mask dialog box. In the upper left is a grayed preview image and below are three sliders, one for Amount of Sharpening in Percent, one for Radius affected in Pixels, and one for Threshold Levels.
I suggest you study the preview carefully and begin to move the sliders to the point the preview features become crisper, but do not overdo the transformation. On a snow scene in my photo archives, I moved the amount to 60% and the radius to 45 pixels and turned a dim photo into a highly detailed work. Your individual shot might need much less of an effect or more and this can only be determined with experimentation initially. After a while the process will become intuitive. I do suggest that before using any filter, you copy the image to a new layer using Ctrl+J.
Okay, that’s enough about Unsharp Mask. After all, this article is about High Pass and I find it a much more user friendly method of working. First we will talk about the Linear Light Method and then the Soft Light Method. Both work well and I use the methods interchangeably. First open an image in Photoshop that you want sharper. Hit Ctrl+J on the keyboard to make a copy of the background layer. Right above the layers, you will see a rectangular button or field that usually has the word “Normal” in it. If you click on this, a drop down box will appear that will give you many choices of blend modes below normal, e.g., darken, multiply, etc. Search down the list and find linear light. Do not be shocked by the appearance of the image after making this change. All of that is about to change. Now go to the same filter menu you went to when finding the Unsharp Mask and look for the Menu Item, Other. Click on this and usually second from the top you will see High Pass. Click on this and the dialog box will open. Initially move the radius slider below the preview to a position between 1.5 and 2.5. You should see the outline of some of your features in the preview box. Click OK and you will notice your image returns to normal, just a bit sharper. Turn off and on the layer to see the difference in effect. I like this method because it sharpens subtlety without introducing excessive noise. If you feel more sharpening is desired, hit Ctrl+Z to undo the change and start over with a higher or lower radius, depending on your visual analysis.
The next method is similar to the one above. Open and copy the original photo to a layer. Make sure the copy layer is active and go to the filters menu and open the High Pass Filter. This time watch the preview and move the radius slider upward. Usually a radius of 7-10 will provide adequate sharpening. If the edges in the grayed preview are crisp, hit okay. Now go back to the blend modes we used before and choose soft light as the blend mode. The grayed image will be removed from the screen and a sharpened original image will appear. Click the layer off and on to see the amount of sharpening this method applied.
I hope you enjoyed this quick tutorial and please check my blog often for more on photography and techniques.
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