a9 May 2012

Tutorial: Sharpening - Part 1: High-Pass Sharpening

HDR photo taken in Masuria, Poland. There was a lot of dust (caused by the car which passed a few seconds before) over the lake when the sun started to set what created this haze like effect.
In this short post and in posts later, I will try to write a few words about sharpening in Photoshop. As it is rather complicated task which one can approach many different ways I will divide this tutorial into a few parts (each of the parts focusing on a different sharpening method).

Today I will talk about one of the most popular sharpening methods known as the High-Pass sharpening.

One of the easiest and most popular methods to sharpen images is known as high-pass sharpening. The name comes from the Photoshop filter used to achieve it (High-Pass filter).

Here is our source photo:

Picture 1: Source photo for this tutorial

And here are the steps to apply this sharpening method:
  1. Open Photoshop.
  2. Open your image.
  3. Duplicate your background layer by pressing CTRL + J.
  4. Change blending mode of the duplicated layer to Overlay. At this stage the image will have a way too much contrast but it will be fixed soon. Note that you can use other blending modes (eg. Soft Light or Hard Light) but the results of the sharpening won't be the same (Soft Light will produce less sharpened image while Hard Light will produce stronger sharpening). Use one which works best for you.
  5. Now from Main Menu select Filter -> Other -> High Pass...
  6. Be sure you have "Preview" checkbox checked.
  7. Change radius and observe how the details get sharpened (and the photo contrast is back to normal). The radius controls strength of sharpening. I usually use values around 2 pixels but this value depends on the image. Using very high values (like 15 or more) seems to produce rather strange results. Also if instead of Overlay blending mode you had Normal mode selected you would get something similar to the Picture 2. The image is grey but there is quite strong contrast around the edges.
  8. Click OK.
  9. If at this point you think that you over sharpened the image, one way to fix this is to reduce layer opacity.
One of the benefits of using high-pass filter sharpening is that it only affects areas that are edges. This means that it won't sharpen noise (what some of the other sharpening methods do).
Picture 2: High-pass filter applied to the source photo.
Finally here is the before/after comparison. Left part of the image uses sharpening method described in this post and the right uses no sharpening. Please note that I over sharpened the left side a little bit to make the difference more significant (as the photo already was quite sharp).
Picture 3: before/after comparison.

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