Topic awaiting preservation: Ramble: High, Medium, and Low Frequencies (Page 1 of 1)

Man, I don't know what the deal is lately. My brain is working super duper on several things. Quite a few things that have been in the back of my head for a long time have been coming back up to the surface and making sense all of a sudden. Exciting, yet frustrating. Mixed blessing.

Ramble spotted on yer six.

Frequency: High, Medium, and Low

Using Gauss to get low frequencies is easy. Using High Pass to get low frequencies is just as easy.

- Copy photo
- Gaussian Blur 8
- Copy photo and order to the top
- High Pass 8
- Set to Linear Light 50%

You should be looking at pretty much the same photo. But chances are there will be some minor differences where the high frequencies have high delta over several 'cycles'. You know, like black-white-black over a short distance. A good example of this is thin white text with a black outline.

Anyways, that's the basic idea and technique.

Now, let's blast that basterd some more. You know, give it a real work-out.

- Start with a photo
- New Layer and fill with 50% grey, going to call this 50G
- Copy photo, order to the top, and Gauss 16, going to call this G16
- Another copy to the top, Gauss 8, calling it G8
- Another copy to the top, High Pass 8, calling it HP8

Should look something like this:
- HP8
- G8
- G16
- 50G
- original photo

That's the basic set-up. Now busy time.

For HP8, set to Linear Light 50% and turn it off for the time being. All other layers still on.

- Invert G8, set to Linar Light 50%.
- Favorite method to Copy Merged and Paste
- Call this new layer Medium
- Invert Medium
- Go ahead and trash G8

What we've just done is substracted the opposite to get just the medium frequencies. Then flipped it back over to be proper. To see, try this:

- set Medium to Linear Light 50%
- turn HP8 back on

Should look something like this:
- HP8, Linear Light 50%, turned on
- Medium, Linear Light 50%, turned on
- G16, Normal 100%, turned on

With just those three layers like that, you should still be looking at pretty much the same photograph with very little differences.

While that is high, medium, and low, the low isn't a true low frequency. Functional as is, but let's finish it off. (This goes back to something I was babbling about some months ago. Remember?)

- HP8 off
- Medium off
- G16, Normal 50%
- 50G, Normal 100%
- Favorite method to Copy Merged and Paste
- Call this new layer Low
- Feel free to trash G16

With G16 out of the way, turn things back on for something like this:

- HP8, Linear Light 50%
- Medium, Linear Light 50%
- Low, Linear Light 100%
- 50G, Normal 50%

Congratulations. You've just torn apart a photo into 3 different frequencies.
How you use this ability is up to you. Meh, don't get me started.

Now, if you'll excuse me, I have to catch the last train to Clarksville to meet Mary.

play.fiddle.learn

hehe. nice.

that remembers me of image processing class, when i had to learn all those stuff. doing fast fouries transfrom shifting from image space to frequency space and back.

It is nice, isn't it? I'm really enjoying maniputing detail on several levels using that junk. While I enjoy messing with Luminosity, being able to manipulate only the low frequency Lum is really cool. Keeps everything relative, so to speak. Can even transfer details from one image to another rather easily. Or highlight/shadow tricks, like getting rid of tanlines. It's also a good boost for using Healing/Patch.

I'm vaguely familiar with FFT. I understand the basic idea, but haven't really dug into it yet. One of these days I'll be getting my teeth bloody with it. No idea when, though.

And, speaking of FFT, Roland (finally) did a tutorial that covers a basic FFT technique:
http://retouchpro.com/tutorials/?m=show&id=185

Don't know about you, but I think it's damn snazzy.

(Edited by warjournal on 06-24-2005 01:12)

thanks for the link!

the fft plugin for PS might be useful someday!

Here's the only decent link I can find on image processing and FFT:
http://astronomy.swin.edu.au/~pbourke/analysis/fft2d/

Since FFT is for pattern recognition, I can't help but wonder about some things that have vexed me concerning patterns. Yet another path that I'll be taking a stroll down. Wanna come with me?

I've also heard that the Reindeer Graphics folks have some pretty killer FFT plugs (amoung other things). The author seems to really know his stuff when it comes to scientific/forensic things. I 'heard' him talking about these things and he really blew my mind. Hardcore in a way I've never dreamed of.