It is currently Thu Mar 28, 2024 1:15 pm


All times are UTC - 5 hours [ DST ]



Post new topic Reply to topic  [ 7 posts ] 
Author Message
 Post subject: Improving (maybe) High Pass filter script by RobA
PostPosted: Mon Mar 04, 2013 10:33 pm  (#1) 
Offline
GimpChat Member
User avatar

Joined: May 26, 2012
Posts: 342
Location: France
While I was already satisfied by the old version of the script I had, I stumbled upon the updated version (of aug 2012) on registry: http://registry.gimp.org/node/7385 Then I began to read the comments and someone pointed out, in 2010, how PS handled this high pass filter:
Blacklemon67 wrote:
duplicate, blur, set layer blend mode to grain extract, merge down.
This looks more (to me at least) like photoshop's high-pass. It's more defined then the other one.

Then robA considered the comment and changed his script accordingly.

Reading this comment made me want to reproduce the filter manually, but instead of 'blur' I tried 'selective gaussian blur' (blur radius 5 & max delta 50) then overlaid twice, and this manual output appeared very good to me, especially because with the filter I had side effects making some dark areas darker (visible when dark contours are close to a dark area) and creating slight halos, side effects that didn't came up with the manual way. Looking twice, It seems the output I had was, above all, softer than the filter thus it would allow smooth high pass if needed and stronger if wanted by duplicating high pass overlay layer or using another blend mode.

Picture demo with a Public Domain photo:


Attachments:
File comment: go full screen to see the differences
high pass vs high pass.jpg
high pass vs high pass.jpg [ 759.03 KiB | Viewed 2917 times ]
Share on Facebook Share on Twitter Share on Orkut Share on Digg Share on MySpace Share on Delicious Share on Technorati
Top
 Post subject: Re: Improving (maybe) High Pass filter script by RobA
PostPosted: Tue Mar 05, 2013 1:04 am  (#2) 
Offline
GimpChat Member
User avatar

Joined: Aug 16, 2012
Posts: 4271
Location: Göteborg, Sweden
anarkhya: thank you! i tried that and it worked very well on a picture where it was needed. i'll remember that selective gaussian blur thing.

_________________


Top
 Post subject: Re: Improving (maybe) High Pass filter script by RobA
PostPosted: Tue Mar 05, 2013 1:54 pm  (#3) 
Offline
GimpChat Member

Joined: Dec 27, 2012
Posts: 393
Location: England
The manual image is best. The colours on the filter image are too bright and tend to make the bricks rather unrealistic - I've worked in the construction industry for thirty years so know a bit about brickwork.
I've tried the filter a couple of times, just playing around time, and thought it was pretty good. I'll try out this manual method next time. Thanks for the info.

_________________
Image

DeviantArt gallery


Top
 Post subject: Re: Improving (maybe) High Pass filter script by RobA
PostPosted: Sun Mar 24, 2013 10:55 am  (#4) 
Offline
Script Coder
User avatar

Joined: Jul 14, 2010
Posts: 697
Whatever it takes to get the result you want, is what you should use.

Mathematically, a high pass filter removes the low frequency components of the image, leaving the high frequency components (hence high-pass), which can be done by a blur (convolution) on the image.

Using the selective Gaussian blur to come up with a better overlay seem to give great results - it just isn't a straight high-pass filter, as the frequency that is eliminated varies based on the source image, rather than a single number (the blur radius).

-Rob A>

_________________
Image
Fantasy Cartography and Mapping by RobA


Top
 Post subject: Re: Improving (maybe) High Pass filter script by RobA
PostPosted: Sun Mar 24, 2013 2:53 pm  (#5) 
Offline
GimpChat Member
User avatar

Joined: May 26, 2012
Posts: 342
Location: France
Err.. So, are you saying that is not an high pass filter anymore ? Then I should learn how to make a script..


Top
 Post subject: Re: Improving (maybe) High Pass filter script by RobA
PostPosted: Mon Mar 25, 2013 2:44 pm  (#6) 
Offline
Script Coder
User avatar

Joined: Jul 14, 2010
Posts: 697
anarkhya wrote:
Err.. So, are you saying that is not an high pass filter anymore ? Then I should learn how to make a script..


Right! It is a filter, and a useful one, just not a standard high pass filter.

Like, a Gaussian blur is (by definition) a low pass filter (it removed high frequency details/sharp edges). And a Selective Gaussian Blur is a low pass filter in tandem with an edge protection mechanism (it removes high frequency details, but preserves edges).

You might find through experimentation that is better to use the selective Gaussian blur repeatedly, with weaker settings than one large blur.

-Rob A>

_________________
Image
Fantasy Cartography and Mapping by RobA


Top
 Post subject: Re: Improving (maybe) High Pass filter script by RobA
PostPosted: Mon Mar 25, 2013 4:31 pm  (#7) 
Offline
Administrator
User avatar

Joined: Aug 10, 2012
Posts: 12978
Location: Native to NYC living in Arizona, Gimp 2.8 & 2.10, Win 11 PC.
I've known about the manual way of creating a 'high-pass' effect, but have never used a 'selective gaussian blur'.

I'll have to try this out as how RobA suggested, with weaker settings and multiple 'selective gaussian bluing' than just one large blur.

Thanks! ;)

_________________
Image
"A wise man learns more from a foolish question than a fool can learn from a wise answer"
Image


Top
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 5 hours [ DST ]


   Similar Topics   Replies 
No new posts Attachment(s) GEGL Sharpen Plugin with many high pass algorithms

0

No new posts Distort and RobA's Chisel script

2

No new posts Attachment(s) Script-fu Scale Pattern by RobA for Gimp 2.10

8

No new posts Attachment(s) How to pass textvariable to GMIC from python [solved]

3

No new posts Attachment(s) The High Altitude Mobiles Of Maldonia

4



* Login  



Powered by phpBB3 © phpBB Group