4 Replies Latest reply: Apr 6, 2013 6:53 PM by Steve Zeeeee RSS

    when, why, and how the high pass filter

    Steve Zeeeee Community Member

      i have a good grasp of the arcane nuances of unsharp mask,

      but nothing on high pass filter,  So can someone offer just a

      summary of the thinking of when we select that tool, and

      what parameters to consider to what end.  Thanks a lot

      best,
      Steve z

        • 1. Re: when, why, and how the high pass filter
          c.pfaffenbichler Community Member

          when we select that tool

          »Tool« has a specific meaning in Photoshop, »High Pass« is a »Filter«.

           

          For an explanation of the connection to Gaussian Blur check out:

          http://en.wikipedia.org/wiki/High-pass_filter

           

          High Pass can not only be used for sharpening but can also helpful for extracting patterns from images.

          Edit: I should have clarified that I meant Patterns intended for use as Linear Light Pattern Overlays to allow painting on a Layer while maintaing a sctructure on the paint strokes to better fit in existing images.

          • 2. Re: when, why, and how the high pass filter
            RWSP Community Member

            Jeff Schewe, in his new book “The Digital Negative” (Peachpit Press) describes a use of the High Pass filter to adjust midtone contrast -- bring up midtone contrast details -- somewhat like the Clarity adjustment in camera raw, but “you have a lot more control over the parameters.”  He applies a High Pass to a layer copy of an image with blend mode set to Overlay and using Blend If options to constrain effect to the middle range of levels in the image. (pg 210-212)

            • 3. Re: when, why, and how the high pass filter
              Jeff Schewe Community Member

              The high pass filter is a tool for finding edges...from that, you can adjust the edge width to increase or decrease the radius of the edges. Everything that is not an "edge" turns into a middle grays. Depending on the blending, this give an opportunity to modify edge or non-edge values. Overlay lightens the lights while darkening the darks and does nothing at 50% grays In the case of high pass, this means the light side of the edges gets lighter and the dark edges darker. This can have a sharpening effect similar to USM without the threashold control.

               

              If the HP radius is small, the effect is sharpening...if the radius is larger, it's more of a tone /contrast control. If you constrain the effects using Blend If adjustments, you can impact midtone contrast as mentioned by Robert.

              • 4. Re: when, why, and how the high pass filter
                Steve Zeeeee Community Member

                thank you.

                i'll study this and i hope i have no more questions,

                but i wonder everything, like generally, for less

                sophisticated purposes, when do you turn to it.

                High frequency stuff, low; why this not unsharp mask,

                that kind of thing.