Episode 127: Octave Sharpening

127Download the Video! (38.4 MB, 20:13)
Download the Companion File!

A posting in the forum pointed me to a description of an interesting way to sharpen an image. This Octave Sharpening is useful when you have to do a lot of sharpening and want to avoid the typical halos around the edges.

The secret lies in a combination of 4 USM sharpened layers with different opacity. As in the recipe I used an amount of 5 (500% in the Other Program), threshold 0 and 0.5, 1, 2 and 4 in the different layers. The opacity was set to 100%, 50%, 25% and 12.5%. The more sharpening the less impact in the image. But the traces of harsh sharpening give a bit of a gradient to the edges in the final image.

Norman needs some information about old slide producers in Israel. Are you able to help?

And I have started to use Google Wave for episode planning. If you want to participate, drop me a line at info@meetthegimp.org . I also have some invites.

The TOC

00:30 Torrent for the first 100 shows
02:10 Grandfatherclock tutorial in writing at meetthegimp.org
03:10 Help for Norman
04:00 Google Wave
04:40 Octave sharpening
06:20 TAB hides the dialogs
06:50 Octave sharpening in action
08:00 50% Zoom for sharpening
08:10 Sharpen the 4 layers
11:20 setting the opacity
12:00 Looking at the result
13:15 Layer group workaround
14:30 Recap
17:10 Forum
17:00 Fund raising

Creative Commons License
Meet the GIMP Video Podcast by Rolf Steinort and Philippe Demartin is licensed under a Creative Commons Attribution-Share Alike 3.0 Germany License.
Permissions beyond the scope of this license may be available at http://meetthegimp.org.

23 thoughts on “Episode 127: Octave Sharpening

  1. Hi,

    nice show again. I have to try this technique myself, it looks quite interesting and I have never seen it before.

    Greetings
    Fornit

    PS: The reason for looking on a picture at 50% zoom is (so I’ve heard in some other tutorials), that the look of the sharpening is nearly the same as in a print at 50%. I don’t know, if this is true because I don’t print to much pictures.

  2. Thank you, it’s one of the best shows of the last weeks! And already show number 1111111 :D At least according to the video…

    One addition: You should have set the layer modes to Value to avoid strange coloured halos.

  3. For a quick and dirty way you can use a script to sharpen a load of images at once. Useful especially for scanned drawings on not-so-good paper when there’s no time to edit each one. I’ve seen that at the book fair when lots of fanart is scanned to be put on the big screens.
    I’ve had this script for a while already, but never really used it that much.
    And the term “octave sharpening” was unfamiliar to me until this episode, I know this technique as fanart filter.

    #!/bin/bash
    B=”`basename “$1″ .png`”
    convert “$1″ -unsharp 1×1+5 “$B”_1.png
    convert “$1″ -unsharp 2×1+5 “$B”_2.png
    convert “$1″ -unsharp 4×1+5 “$B”_4.png
    convert “$1″ -unsharp 0.5×1+5 “$B”_5.png
    composite -blend 50 “$B”_1.png “$B”_5.png “$B”_t1.png
    composite -blend 25 “$B”_2.png “$B”_t1.png “$B”_t2.png
    composite -blend 12.5 “$B”_4.png “$B”_t2.png -quality 9 “$B”_result.png
    rm -f “$B”_5.png “$B”_1.png “$B”_2.png “$B”_4.png “$B”_t1.png “$B”_t2.png

  4. Thanks for posting this. I can really need this, I have tons of pictures that need basic sharpening and are not so important to spend manual time.
    Now, how does this work? I have copied the script into a text level but it just sits there. Do I need to set it to some special level mode? And how will it work on all pictures? I tried open all of them but Gimp crashed and I had to press reset to get it back working. I’m sure it works another way then scripts for a single picture but I dont know how.

  5. @ Kevin: That script runs independently of GIMP. It’s ImageMagick. Just run it in your terminal…

    @ Rolf: Ah, so this was by purpose. Very cool. It really fits the title…

  6. @ Mathias: We once had a little conversation about English expressions so, I hope you don’t mind but it is ‘on purpose’ meaning deliberate, not ‘by purpose’.

  7. @ Kevin: It depends on your operating system. In Windows, install ImageMagick from: http://www.imagemagick.org/script/binary-releases.php?ImageMagick=l1amk6vj42b1tgcjj85iqh2op0#windows
    Afterwards, go to the start menu, click on “Run Process” (or however it is named) and type “cmd”. Then you get your terminal.
    But I guess this script is not working in Windows. You need to type those convert commands manually or write your own BAT file.

    @ Norman: Thank you!

  8. Can’t get the right companion file down onto my computer. I got companions from episode 121 instead.
    BTW interesting technique, happy to see this used on pictures in a challenge.

    (Edit by Rolf: I have fixed the typo!)

  9. One tips for sharpening is to do this:
    1 Copy the original picture to two layers,
    2 Do a rather hard unsharpen mask on both layers
    3 On the first layer select darken
    4 On the second layer select lighten

    Now can you change the transparency of the layers to select how hard the sharpening shall be and you can make the darker part of the sharpen very faint just by changing the transparency of the darken layer, or to do the white part fainter by changing the transparency on the lighten layer.

  10. Okay, I found this cmd program. I didn’t know this. But how does it work? I get a empty black window and nothing happens. I dragged the pictures in there but it does nothing. Or does it take very long? I have many thousand pictures.

  11. Kevin, the file above is a script for a Linux computer – should work on a Mac too. It has to be translated into a Windows Batch File, a .BAT . (I can’t do that, I left Windows before 95 hit the market.)

    If you have someone near you who has good Windows knowledge it can be set up in a way that you only pull your images on an icon to convert them. But it is difficult to do without sitting at the machine.

  12. Rolf >>> In the podcast, you say that people recommend viewing the image at 50% size while sharpening, but you don’t know why. Here’s what Lee Varis says about this in his tutorial, which you give a link to in the podcast:

    “Many will advise you to look at the sharpen filter at
    100% view – I used to do this myself. The effect of
    sharpening at this magnification will look at lot more
    drastic than it will look at the final printed size. The
    tendency, for most photographers especially, is to
    under sharpen because of this. When you are zoomed
    to 50% you are looking at the size of the image at
    aprox.. 150 pixels per inch. Most of the time you are
    sharpening to size at 300 pixels per inch – by sharp-
    ening at the 150 ppi size you can compensate for the
    lower screen resolution of 72 ppi – the best compro-
    mise to view the intensity of the effect.”

  13. Well, lets hope Gimp gets more than 8 bits before your shownumbers.

    Just looked through ALL shows during the last week. And I think I learned a lot more about Gimp than in the last five years. Thank you two!

    And I’m really happy that Rolf started to duplicate things instead of doubling them at some point.

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