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Flora 05-31-2012 01:23 PM

Basic Image Correction with Frequency Separation
 
12 Attachment(s)
For me, Frequency Separation started here... I found the Tutorial very interesting, a bit beyond my knowledge, and hadn't a clue about the possible use of separating an image into:
  • a Blurred version = LOW FREQUENCY and

  • a High Pass version = HIGH FREQUENCY


Only after 'stumbling' upon several articles and Tutorials on the topic, and with the help of Murray (mistermonday) did I realize the incredible utility and power of this technique.

Now, the High Pass part of the Separation has been substituted with a more accurate procedure after which blending together the "separated" parts of the image and comparing the result with the original, gives a negligible or no difference ... (particularly so if working on 16 bits images)

That said, .. why on earth separate an image into different frequencies only to blend the frequencies back together trying to 'reconstruct' the original ???

.. Here is why ...


Separating your image into LOW and HIGH Frequencies allows you to correct each problem where it really is, minimizing the effect/damage of this corrections on the other parts/Frequencies.

*For this Tutorial I used a cropped version of this image from our Archive.


In my opinion, Frequency Separation is the best technique for 'fine tuning' meaning you should do the 'big' corrections before .. and that's what I did with this image where I, first, minimized the magenta discolouration on the little boy's face by selecting it with Select>Color Range and then corrected it with Image>Adjustments>Replace Color.


.. and then the Frequency Separation:
  • Let's start by duplicating the background (or corrected Layer) twice (keep your Background unchanged for comparison)

  • name the first Duplicate LOW and the top one HIGH

  • Hide the HIGH Layer by clicking on the eye at its left

  • Click on the LOW Layer to highlight it and go to Filter>Blur>Gaussian Blur

The aim is to blur your image so that most 'blemishes' fade away... so for each image the amount of Blur will be different.

  • After blurring the LOW Layer, click on the HIGH Layer and make it visible again by clicking on the 'missing' eye at its left.
  • Go to Image>Apply Image and change as per attachment (8 Bits Images)


or to Image>Apply Image as per attachment (16 Bits Images)

  • Change the Blending of the modified HIGH Layer to Linear light and, apparently we are back to square 1 ...

... Yes ... we are, but now our image is divided into two different frequencies allowing us to "correct each problem where it really is, minimizing the effect/damage of this corrections on the other parts/Frequencies."


Attached a PS action for this procedure which will let you adjust the Gaussian Blur Radius.

But let's see how this works ...

I usually start my corrections on the LOW Layer with a very soft (fuzzy) brush (low Opacity & Flow) and, sampling from areas surrounding the parts I want to correct, I gradually paint over them ..

TIP:*While working on one Frequency Layer I switch on and off the visibility of the other Frequency Layer to check the result on the 'whole' image*


Next I work on the HIGH Layer where I use first (and where possible) the Spot Healing Brush then, if necessary, I go for the Healing Brush ...

TIP:* Sorry ... had forgotten to add that when using any of the Heal Brushes or the Clone Tool, set the 'Sample' to Current Layer to avoid adding unwanted colour to the HIGH Layer.*



*(I increased the contrast of the HIGH Layer for better visibility for this Tutorial)*


TIP:*Using the Frequency Separation Technique, you will notice that the 'bleeding' of both Healing Tools is minimized ... but still shows when healing close to edges ... In this case, I switch to the 'Replace' Blending Mode and go back to the Normal Blending Mode when 'out of danger zone' ...*


My result so far ... (I left the scars on the little boy's forehead on purpose..)


Thank you so much Murray for helping me understand Frequency Separation better with your .pdf Tutorial (have to find a way to reduce its size to 200 KB to be able to upload it here) ... and for the link to this Great Tutorial

Well, the Frequency Separation technique has 'changed' since I first stumbled upon it ... Now we have the Asymmetric Frequency Separation which has the addition of a COLOUR Layer... Maybe another Tutorial ...:wink:

What actually got me 'going' with the Frequency Separation Technique was this Tutorial by Der_W.

If you wish to dig deeper into this topic, you could start here

Hope this helps :)

0lBaldy 05-31-2012 02:47 PM

Re: Basic Image Correction with Frequency Separati
 
Thank you Flora for your easy to understand instructions that helped me finally figure out where I've been going wrong with this procedure for such a long, long time!! TY, TY, TY... I had read and tried almost everything but just could not wrap my head around it.. :bow:

Thanks again for clearing up some of the very Grey areas in this feeble old mind! :)

ratpat13 05-31-2012 10:50 PM

Re: Basic Image Correction with Frequency Separati
 
2 Attachment(s)
I would just add one possible comment and a suggestion that some people might like to add to the frequency separation workflow.

When it comes to work in the High frequency layer with clone or healing tools it's important to remember (especially if your using the cloning tool) to turn off "Sample all Layers." With the clone tool in particular you want to make sure it's set to "Current Layer." Otherwise you'll end up bring in Low Frequency color information into your High layer.

For workflow, I like to work as nondestructive as possible on the High Frequency layer incase I need to go back to some of the original texture. To do this I duplicate the High frequency layer, set it's blend mode to normal and clip it to the High frequency layer bellow. You can now do all your cloning on the clipped HF layer without damaging the original. It takes up a little more file size but gives me the added flexibility.

I've included a screen shot of the setup and a copy of my action that sets it up this way.
Just to note this action runs off the background layer, if you want me to change the action to run anywhere within your layer stack just let me know.

Flora 06-01-2012 12:18 AM

Re: Basic Image Correction with Frequency Separati
 
Hi,

0lBaldy
,

thank you so much for your feedback and kindness!!!

So glad this Tut could help you! :)

ratpat13,

thank you so much for your help and action!!! :thumbsup:

I woke up 'remembering' that I had forgotten the 'Current Layer' only in the part concerning the Healing and I logged in to add it !!!

ratpat13 06-01-2012 12:37 AM

Re: Basic Image Correction with Frequency Separati
 
Not a problem.

Flora 06-01-2012 12:55 AM

Re: Basic Image Correction with Frequency Separati
 
Quote:

Originally Posted by ratpat13 (Post 308349)
.....For workflow, I like to work as nondestructive as possible on the High Frequency layer incase I need to go back to some of the original texture. To do this I duplicate the High frequency layer, set it's blend mode to normal and clip it to the High frequency layer bellow. You can now do all your cloning on the clipped HF layer without damaging the original. It takes up a little more file size but gives me the added flexibility.

Just great! Thank you!! :bigthmb:

ratpat13 06-01-2012 04:16 AM

Re: Basic Image Correction with Frequency Separati
 
1 Attachment(s)
Updated the action to take care of a problem being discussed in another form. Most of the frequency separation actions involve duplicating the background layer which isn't helpful if your file already has several layers or you have renamed your background layer.

This updated action can be run from any layer in your stack regardless of the background layer.

Flora 06-01-2012 04:51 AM

Re: Basic Image Correction with Frequency Separati
 
Quote:

Originally Posted by ratpat13 (Post 308359)
Updated the action to take care of a problem being discussed in another form. Most of the frequency separation actions involve duplicating the background layer which isn't helpful if your file already has several layers or you have renamed your background layer.

This updated action can be run from any layer in your stack regardless of the background layer.

Hi again,

even though I rather keep the background 'untouched' for quick comparison, I agree about 'thinning' down the number of the layers ...

As for the possible problem of 'renaming the background', or any Layer, when writing actions, I learnt to use keyboard shortcuts to select Layers without recording any specific name ... (if you try my action attached to the Tutorial you'll see that)

Here you can find my post + links about these very useful shortcuts on another Thread.

Der_W 06-01-2012 08:21 AM

Re: Basic Image Correction with Frequency Separati
 
Hi Flora,

great tutorial, thanks so much :-)!
Did you also plan on including some information about the asymmetric frequency separation as well (and if so, did Murray send you the updated information about it which we found out about in a recent private discussion)?

Flora 06-01-2012 08:53 AM

Re: Basic Image Correction with Frequency Separati
 
Hi!!! Thank you so much for your feedback and great to 'see' you!!

Quote:

Originally Posted by Der_W (Post 308366)
Hi Flora,

great tutorial, thanks so much :-)!
Did you also plan on including some information about the asymmetric frequency separation as well (and if so, did Murray send you the updated information about it which we found out about in a recent private discussion)?

Originally I had thought of making the Tutorial including the Asymmetric Frequency Separation ... but changed my mind and opted for the 'a step at a time' solution.

Murray sent me everything ... Thank you so much for helping out with your much appreciated tips and updates!!

I don't know yet, but I might try a 'Basic' Tut on Asymmetric Frequency Separation as well ... By the way, I call the Tuts Basic 'cause I wish to keep them clear and simple so everybody can follow them.

Actually, it was your video Tutorial .. (the one linked) that got me going with the Freq. Sep. ... Got any new videos on the Asymmetric version?

Thanks again ... and could I knock on your door in case I need more help? :o:


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