High Pass Filter in GIMP (new plugin)
I am not sure if this should be in the resources section or in the tutorial section, but here it is, anyway.
GIMP doesn't have a high pass filter. I had previously posted about "faking" a high pass filter with GIMP to get rid of pattern noise in this post.
Then Redrobes posted a great thread on creating seamless textures that relied heavily on high pass filters.
More recently, I cam across a few external posts on sharpenning images using high pass filter overlays, rather than unsharp masking (for photoshop).
Because of all that I decided to write a high pass filter plugin. Just unzip the attached file into your scripts directory. It shows up asFilters->Generic->High Pass Filter.
You can select a blur radius that sets the size of detail to be passed by the filter, a contrast adjustment, as well as an option to keep the source layer or replace it.
I actually implemented 5 different high pass modes.
- Colour - I think this is the same as photoshop's high pass filter effect.
- Preserve DC - like colour, but adds the average image colour back in.
- Greyscale - this greyscales the layer before high pass filtering.
- Greyscale, Apply Chroma - as above, but blends it in with the source layer colours
- Redrobes - (for lack of a better name :) ) follows the procedure in post #17 of this thread
Here are samples of the 5 filter modes:
And various blur amounts:
The default blur (10) with different contrast adjustments:
And a sample how a high pass filter can be used to make a nifty overlay for a map: