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Thread started 06 Sep 2010 (Monday) 11:55
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Visual (Spatial) Frequencies for Retouching

 
seanbaker
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Sep 06, 2010 11:55 |  #1

I've written a series of tutorials on the topic of spatial / visual frequencies as a part of retouching work which I thought the membership here might enjoy. They remind me a lot of old conversations we had on similar topics for skin work here when I had more time to post.

While I'm well aware that it's poor internet etiquette to just post a link to one's self, I hope that you'll read a segment or two before condemning me - these are long entries, and would be a bit much to have in a thread which I'd rather focus on discussion of the matter.

In any case, I hope they help!

Visual Frequencies - a Primer (external link)
VF - Tools of the Trade (external link)
VF - The Mechanics (external link)
VF - Why, Sean, Why?!? (external link)
VF - Dirty Secrets, Dirty Tricks (external link)

Happy Labor Day!


Sean Baker

  
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Kent ­ Clark
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Sep 06, 2010 13:10 |  #2

Sean, these are great. The big gripe I have about most PS and LR content is that it just hashes over the same things that are in the help files. It's nice to learn something new.




  
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René ­ Damkot
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Sep 06, 2010 17:02 |  #3

That will keep me in reading for tomorrow :)


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D ­ Thompson
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Sep 06, 2010 22:24 |  #4

Thanks, hopefully will get an understanding of this technique.


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seanbaker
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Sep 07, 2010 04:24 |  #5

Thanks guys! FWIW, I'll be attempting a few video followups for this - I know that reading such lengthy material isn't the easiest way for everyone to learn.


Sean Baker

  
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kirkt
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Sep 07, 2010 09:09 |  #6

It's like a lightbulb just went on ....

I have been using FFT and frequency-based filtering for a while to isolate and to correct certain regular pattern features in images, but separating an image into frequency components for retouching never crossed my mind. I just downloaded your actions, opened a casual snapshot portrait I happened to have on my computer and, after studying the image for a few minutes, could visualize which corrections fell into which frequency band. I ran a 2 layer separation and within a few minutes had cloned out high-frequency blemishes and stray hair on the high-freq layer and reduced redness in the chin and cheek areas on the low frequency layer. I don't really do retouching, but now I can see how, in a few minutes, those kind of corrections will become standard. This is similar to the revelation of separating luminance from color information in Lab.

Thanks for sharing, this is very cool. I appreciate the effort.

Kirk


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cmchavis
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Sep 07, 2010 12:13 as a reply to  @ kirkt's post |  #7

Nice effort - I remember what it was like trudging through the Highpass sucks thread and how much time it took trying a method, then comparing it to previous results and trying to figure out if it was easier or harder or even did what it was supposed to do. Your "synopsis" is a nice breakdown of the information.

It's pretty cool seeing an image split up and come together via all the bands.

Also, I must have missed the -50 contrast correction to the HP filter - I didn't know you could 'fix' it - been using the Apply Image 'fix' since I'm used to that from Dan Margulis's image correction stuff.

Good work, I had dreams of doing the same, but am way less ambitious.




  
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seanbaker
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Sep 07, 2010 14:54 |  #8

Kirk - Way to go, spoiling my FFT followup surprise! :P Glad to hear it helped!

cmchavis - The HP filter's 'brokenness' was just its naive (or brilliant, depending on how you want to look at it) design. we just had to overcome that naivete (as well our own as to WTH was going on).


Sean Baker

  
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FatCat0
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Sep 07, 2010 23:17 |  #9

Ahhhh physics applied to post processing. You've made my day...reading......




  
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kirkt
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Sep 08, 2010 08:32 |  #10

Sorry about that - I'll pretend I've never heard of it. Post away!

Kirk


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René ­ Damkot
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Sep 14, 2010 07:57 |  #11

Been reading for quite a while.
Useful stuff.

Obviously very nifty for retouching people.
Have to try the results for sharpening compared to other methods.

Trying to come up with uses of bandstop and bandpass. Might come in handy as well. :)

Edit: Ah. Another lightbulb: Separating a portrait shot into low-medium and high frequencies, then masking off the medium frequencies for a quick smoothing of the skin. Nice.


As for the differences between the "Apply Image" method and photoshops "HighPass" filter followed by a contrast -50: Not that big of a difference from what I see...
And the latter can be used on smart objects. (With the Brightness/contrast as a clipped adjustment layer). Nifty :mrgreen:

Side note: Would be nice to have a link on the bottom of the articles to the next article for ease of browsing.


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seanbaker
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Sep 15, 2010 05:30 |  #12

René Damkot wrote in post #10905790 (external link)
Have to try the results for sharpening compared to other methods.

Be sure to try sharpening with 'medium-high' frequencies like 1.5px-0.5px. By removing the finest detail, some of the oversharpened aesthetic can be avoided. You can also use noise reduction in the same way that we discussed using Median / Surface Blur / etc. in order to minimize artifacting, yet not really changing the image (great if you want to sharpen an image which you want to retain its grittiness).

René Damkot wrote in post #10905790 (external link)
As for the differences between the "Apply Image" method and photoshops "HighPass" filter followed by a contrast -50: Not that big of a difference from what I see...
And the latter can be used on smart objects. (With the Brightness/contrast as a clipped adjustment layer). Nifty :mrgreen:

Be careful with this for anything but a bandstop filter (and even then sometimes) - the -50 contrast has to come before the HP filter is applied, otherwise its clipping will always come into play. You can, however, create a SO of the image, and then edit that SO to include a -50 Contrast adjustment layer so that you retain a nondestructive / adaptive workflow, but get the advantage of working entirely with SOs.

René Damkot wrote in post #10905790 (external link)
Side note: Would be nice to have a link on the bottom of the articles to the next article for ease of browsing.

Good point - I'll add that in this evening. Thanks!


Sean Baker

  
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René ­ Damkot
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Sep 15, 2010 14:45 |  #13

seanbaker wrote in post #10912485 (external link)
Be careful with this for anything but a bandstop filter (and even then sometimes) - the -50 contrast has to come before the HP filter is applied, otherwise its clipping will always come into play. You can, however, create a SO of the image, and then edit that SO to include a -50 Contrast adjustment layer so that you retain a nondestructive / adaptive workflow, but get the advantage of working entirely with SOs.

Hadn't thought about including the -50 contrast into the SO. I now duplicate the SO, then add the -50 contrast as an adjustment layer. That means it's applied after the HP filter though.
Better to apply it as an adjustment inside the SO indeed.
Good point :)


"I think the idea of art kills creativity" - Douglas Adams
Why Color Management.
Color Problems? Click here.
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PERSONAL MESSAGING REGARDING SELLING OR BUYING ITEMS WITH MEMBERS WHO HAVE NO POSTS IN FORUMS AND/OR WHO YOU DO NOT KNOW FROM FORUMS IS HEREBY DECLARED STRICTLY STUPID AND YOU WILL GET BURNED.

  
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Visual (Spatial) Frequencies for Retouching
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