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Frequency separation math

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  #11  
Old 09-16-2014, 01:07 PM
nemrob nemrob is offline
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Re: Frequency separation math

Thank you, Murray! Step by step I'm getting closer understanding it. Now I get the 8bit offset.
For the 16 bit, if Add inverted is Subtract, why not using it in the first place?
I have to chew on the signed bits, but I'm progressing

Thank you for the action.
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  #12  
Old 09-16-2014, 01:11 PM
klev klev is offline
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Re: Frequency separation math

Quote:
Originally Posted by mistermonday View Post
Rob, 115/32767 is the same as 1.23/256. You can get into minutia of the math but you don't need to waste your time to appreciate the approx error and the fact that everything Photoshop does has an underlying set of math algorithms and calculations going on.
That is true, and it's another cause of some amount of grief when you guys use this strategy.

Note haloing/ringing. You can see it best along the blue edge.
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  #13  
Old 09-18-2014, 12:02 AM
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Aladdin Aladdin is offline
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Re: Frequency separation math

Murray & Klev: Do you guys study this stuff? what you do? Just curious.
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  #14  
Old 09-18-2014, 01:45 AM
klev klev is offline
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Re: Frequency separation math

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Originally Posted by Aladdin View Post
Murray & Klev: Do you guys study this stuff? what you do? Just curious.
Magic 8 ball says "yes", at least in my case. It's a combination of books and research papers. If you're interested in a specific area, I can probably suggest some preliminary reading. Photoshop will allow you to implement custom filtering, but if you wish to run formal tests, I suggest something like Octave.
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  #15  
Old 09-18-2014, 11:25 AM
Smart Object Smart Object is offline
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Re: Frequency separation math

Hi guys, forget about the numbers. I will show you a trick to get FS layers easier - with no need to remember the Apply image settings...

1. make a stamp (Ctrl + Shift + Alt + E), name it Low Freqency
2. Invert the Low Frequency layer (Ctrl +I) and set opacity to 50%. What you see now is mid grey.
3. Go to filters - gaussian blur, check the Preview and select radius you need. You can actually see the High Frequency now.
4. Make a stamp, name it High Frequency and change blending to Linear light
5. Select Low Frequency layer, invert it back and set opacity to 100%

Done, you can start retouching.

Optionally, to see the skin texture better in step 3, make a temporary Curves layer with settings like: black point Input - 100, white point Input - 155. (Make this layer after step 2, delete it after step 3 ...)

This technique works both with 8 and 16 bit files.

Enjoy

p.s.: i am planning to make some actions/scripts for frequency separation, subscribe to the newsletter at photoshopchef.com and i will give you know ...
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  #16  
Old 09-19-2014, 05:43 AM
nemrob nemrob is offline
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Re: Frequency separation math

Yes, your method is working and easy. Thank you Smart!
I've tried all the methods I know (3+the simple HP method that "sucks"), and this one is just as good as the Apply image split.

BTW the 3rd method was the HP+Brightness/contrast (contrast -50, on legacy) that should be just as good as the Apply image split, but it's just not.
I've made the low pass, then with the same radius the HP, I put it on Linear Light, 100% opacity. Then Brightness/contrast on legacy, -50%.
This should be just as perfect as the Apply image, but it is just not - not a big difference: the light in the pupil is less white, but still - I read this shoud be perfect. Am I doing something wrong or is it the method that's faulty?
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  #17  
Old 09-19-2014, 06:42 AM
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Der_W Der_W is offline
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Re: Frequency separation math

You need to apply the Brightness/Contrast before applying the high pass.
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  #18  
Old 09-19-2014, 07:09 AM
nemrob nemrob is offline
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Re: Frequency separation math

That was it, thank you!
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  #19  
Old 09-20-2014, 05:34 PM
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byRo byRo is offline
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Re: Frequency separation math

Quote:
Originally Posted by redcrown View Post
You might find your answer here: http://www.modelmayhem.com/po.php?thread_id=439098

That's a forum thread that has been running for over 5 years and has thousands of posts. I believe the OP is the inventor of frequency separation.
Well actually...
We were already talking about frequency separation RIGHT HERE at RetouchPRO quite a long time before this!
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  #20  
Old 09-20-2014, 05:49 PM
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byRo byRo is offline
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Re: Frequency separation math

I prefer separating in three frequencies and not just two.

So, as a bonus - here's an action that I use for separating three frequency bands.
  • First blur is set to show just general face light and dark areas.
  • Second blur is set to just eliminate the details.
  • You can work on the three layers: Lo, Mid and Hi separately.
  • For the Mid and Hi and I use a adjustment layer to make them stand out while working.
Hope you find this useful!

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