High Pass Filter to Gimp

I wanted to edit a photo with the High Pass Filter but I noticed it wasn’t installed yet. The reason for that was that I had made the switch to Ubuntu Linux. I had to search the internet and finally found the plugin that I was looking for, here: http://registry.gimp.org/node/7385.

I had some trouble getting this installed on my computer but the search program Catfish offered the solution. I let the program search for all. scm files (the extension name of all Gimp plugins) and I observed that the plugins on my computer in this location are: /usr/share/gimp/scripts/.

I use the High Pass Filter when I want to sharpen a portion of a picture. One can think of a landscape photo where the foreground is in focus but the background not. The High Pass Filter can rectify this.

A good explanation of the High Pass Filter gives Rolf Steinort from Bremen on his site Meetthegimp.org. Here is the video:
https://blog.meetthegimp.org/episode-164-high-pass-sharpening/

In his video he used not the plugin but he does it manually. He does a number of actions:

  1. He makes 2 new layers of the original picture.
  2. He selects the uppermost layer.
  3. Colours/Inversion of this layer.
  4. Then placing layer mode on Grain Merge. The result is a gray area.
  5. Then Filters/Blur/Gaussian Blur.
  6. Merge with the layer underneath.
  7. Put this layer on layer mode Overlay.
  8. With opacity you are able how much the picture is to be sharpened.

These are quite a few actions and for those who have not understood, I refer to the video created by Mr. Steinort.

But this is what you need to understand. It feels probably counterintuitive that you can sharpen a photo with Blur. That this is possible is the due to the fact that you have made an inversion of the picture at the beginning. In practice, this means that if there is 80% blue in the picture is, that after inversion this is 20%. 20% red becomes 80% red. And 10% green becomes 90 percent green. So you invert the values of the colours in the picture. And this is what you blur.

Paleis Het Loo inverted

Inverted image

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