High Pass Filter in GIMP (new plugin)

[Redrobes]

I have a mode named after me... sniff... its all too much, im gonna cry.

This is great Rob. The only bit I cant quite figure is what is the basic difference between the Preserve DC and 'my' mode since I was trying to make a filter to high pass with preserve DC. It does look similar in the results in any case.

Interesting bit about the stairs. Although I have never procedurally created the staircase pattern I do use one as a transparency to pop over any other type of terrain - like dungeon stone for example.

Have you tried to use the FFT expansion with a DC preserve - ill attach the kind of filter you need. You will have to adjust the levels to suit Gimp tho. Note the center pixel is 'no change' color - DC preserve. Oh yes should also note - if you get that pixel out by one in any direction it all goes to pot. So try moving it about a little if it doesn't work. The way you can get a definitive answer of course is to give the FFT something all white and get its spectrum and that should have just the one single pixel lit - well thats the one that must be no change.

[RobA]

I thought you'd appreciate the honour, especially when I post this up at the Gimp plugin repository 10 years from now someone will say "why is that mode called redrobes?"

I think the difference comes from adding in the extra blur-average, to the average-blur.

The basic algorithm I used for all of them (except the redrobes mode) was:

-duplicate layer
-blur the duplicate
-invert the duplicate
-set the duplicate to 50% opacity, keeping the mode "normal"
-merge it down.

This gives the hpf with a base 10 50% grey.

EDIT: Thanks for the filter. I'm also working to add all of your FFT maps as pick lists in a front-end to the gimp FFT plugin.

-Rob A>