Frequency Separation Technique

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Frequency Separation Technique

Chances are you have already learned what Frequency Separation (FS) technique is, as it became

mainstream in the past few years. However, many FS technique users actually know very little theory

behind it, thus have little control over its implementation. !ve set out to research and collect all the

important and useful information about it, so we can to"ether learn how to become better at it.

#fter we look at the sli"htly "eeky results of my research (my sources at the end of this article), would

also like to share with you a few practical ways of its smart implementation with the help and advice from

my friends$ commercial photo"rapher from %oscow, #leksey &ov"ulya(you may remember Aleksey

from myShooting With Mixed Studio Lightingarticle) and 'orontobased photo"rapher retoucher

%ichael *olos+ynowic+.

Frequency Separation techniqueis virtually a process of decomposin" of the ima"e data into spatial

frequencies, so that we can edit ima"e details in the different frequencies independently. 'here can be any

number of frequencies in each ima"e, and each frequency will contain certain information (based on the

si+e of the details). 'ypically, we break down the information data in our ima"es into hi"h and low

frequencies.

ike in music any audio can be represented in sine waves, we can also break up an ima"e into low and

hi"h frequency sine waves. High frequenciesin an ima"e will contain information about fine details,

such as skin pores, hair, fine lines, skin imperfections (acne, scars, fine lines, etc.).

Low frequenciesare the ima"e data that contains information about volume, tone and color transitions.

n other words$ shadows and li"ht areas, colors and tones. f you look at only the low frequency

information of an ima"e, you mi"ht be able to reco"ni+e the ima"e, but it will not hold any precise detail.

-ou may have seen this optic illusion that eploits the frequency separation principle. f you look at this

ima"e from a normal distance from your computer while readin" this article you will see #lbert

/instein!s photo. 0ow, "et up and walk away from your screen. ook a"ain. *ho do you see now1
http://dovgulya.ru/http://fstoppers.com/author/juliahttp://fstoppers.com/author/juliahttp://www.vibrantshot.com/blog/http://www.vibrantshot.com/blog/http://en.wikipedia.org/wiki/Sine_wavehttp://fstoppers.com/author/juliahttp://www.vibrantshot.com/blog/http://en.wikipedia.org/wiki/Sine_wavehttp://dovgulya.ru/


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/ssentially, this ima"e is a combination of photos of %arilyn %onroe in the low frequency layer and/instein!s in the hi"h frequency layer. *hen you look at the ima"e from a close distance you see the hi"h

spatial frequency ima"e (/instein), the fine details, the outlines of his facial features. 2nce you walk

away, your eyes will ad3ust 4 the 5low pass filter6 of your vision will kick in 4 and you will see the low

spatial frequency ima"e (%arilyn %onroe).

*ithin the di"ital photo"raphy editin" craft, the separation of spatial frequency data in ima"es can be

utili+ed for skin (and not only) retouchin". *hile there are a number of ways to implement the Frequency

Separation technique, the steps you take to "et to the final result will define the amount of time spent and

the quality of the outcome.

Before we begin, I want to make a quick note regarding the use of the High ass filter in the !S

technique" When it is used to se#arate the image into high and low s#atial frequencies, the results are

inaccurate" In other words, after the se#aration your image data is slightly skewed, so you com#romise

the quality of the outcome before you e$en begin retouching"

%ut& 'hat inaccuracy is mainly affecting the #ixels with extreme brightness, and when used smartly, it

can actually be beneficial to the outcome in some situations" I will talk about this later"

et!s first talk about this more accurate al"orithm.

APPLY IMAGE SETUP

7a. &uplicate your 8ack"round layer twice$ the top layer is the base for the hi"h frequency ima"e data

and the bottom duplicate is for the low frequency ima"e data.

7b. 'urn off the visibility of the Hi"h Frequency layer and select the ow Frequency layer.


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9. *ith the ow Frequency layer selected, run the :aussian 8lur filter and choose ;iel Apply Imageand dependin" on what color depth

you!re workin" in your settin"s will be as follows (click to enlar"e)$

)ote that in the Layer dialog you will need to select the layer that contains your Low !requency

*blurred+ image" In my exam#le it is called ust that -Low !requency layer."

>. 0ow chan"e the 8lendin" %ode of the Hi"h Frequency layer to Linear Lightand your overall ima"e

will look eactly as before you started the separation.

-ou!re set up. usually also "roup these two layers, so my ayer stack is more or"ani+ed.
http://fstoppers.com/wp-content/uploads/2013/10/16-8-bit-color-depth.jpg


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From this point on, every retoucher and photo"rapher chooses his or her preferred tools to work their

ma"ic. 8asically, we aim to soften and even out color and tone transitions on the ow Frequency layer,

without affectin" skin teture, which was captured and preserved on the Hi"h Frequency layer.

-ou will normally hear that the Clone Stamp tool or the Healin" 8rush tool with Current ayer Samplin"

settin" and very low Hardness are the tools to work on the ow Frequency layer? the same tools only with

very hi"h Hardness settin"s are your Hi"h Frequency layer tools.

Check out my old video where only used the Healin" 8rush tool. !ve chan"ed my ways drasticallysince then, but we!ll talk about that later. 'he "oal of this video was to show how fast this technique can

be, so you will see a countdown clock at the top of my screen 4 9@ minutes, boomA

HIGH PASS FILTE SETUP

High Pass filter setup for the Frequency Separation techniqueisn!t all that bad, and shouldn!t be

completely written off as an inaccurate way to separate spatial frequencies.

#s mentioned before, when Hi"h ;ass filter is applied to the Hi"h Frequency layer in place of the #pply

ma"e function, it "ives you an imprecise final ima"e where the bri"htest piels are usually "rayed out.#ccordin" to my friend #leksey, it actually plays out well when you are retouchin" skin with a bit of

overeposed hi"hli"hts on it. 'hey "et toned down and the skin looks more matte as a result. 2ther parts

of the photo where you wouldn!t want the hi"hli"hts to be muted down (such as specular hi"hli"hts on

the lips, catchli"hts in the eyes, etc.) can be easily covered up with a ayer %ask.

#leksey also insists that it!s a very quick method, and should be used alon" with the #pply ma"e FS

al"orithm when appropriate. He eplains that usin" the Hi"h ;ass filter "ives you more control in

decidin" what information belon"s on the Hi"h Frequency layer and what should be blurred out on the

ow Frequency layer. 'his way, after you!ve performed the separation, your further retouchin" should be

much faster and precise.

Here!s how #leksey eplains how he selects the correct Hi"h ;ass radius.

For eample, we!ve "ot this photo to retouch. 'here are some problems that should be taken care of on

the ow Frequency layer such as shadows, lar"er areas of colors and tones that we need to soften or

remove. 2n the other hand, there are also little blemishes on the skin teture, which should be handled on

the Hi"h Frequency layer.


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'o separate spatial frequencies with the Hi"h ;ass filter, we need to create two duplicate layers, 3ust like

in the #pply ma"e approach. 'he top layer will contain our Hi"h Frequency ima"e data and the bottom

layer will be our ow Frequency layer.

*e select the Hi"h Frequency layer, apply the Hi"h ;ass filter to it *!ilter / 0ther / High ass+and

slowly move the


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9p


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#t B.p


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#nd at =.@p


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#ccordin" to my crafty friend, this skin retouch took him only a few minutes because the frequency

spatial data of the ima"e was properly separated. #ll the teture remained intact on the top layer 4 Hi"h

Frequency layer 4 and the colors and tones were quickly evened out underneath it.

5'he #pply ma"e and Hi"h ;ass approaches of separatin" frequency spatial data of an ima"e are the two

main ways of how use the FS technique,6 says #leksey, 5#pply ma"e setup is more accurate, but the

Hi"h ;ass setup is quick and helps me to not only customi+e the separation of skin teture from

underlyin" colors, but also tone down 5hot6 hi"hli"hts on the skin. always "o for the Hi"h ;ass setup

when need to do a quick retouch, especially when evenin" out skin. t is really helpful to be familiar

with and practice both approaches.6


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M!E SMAT +AYS , TIPS F! THE FS TE-H.I/UE

USE

01 A#e2sey uses an a((itiona# e'pty #ayer that he a((s in 3etween the High an( Low Frequency

#ayers1

'here are two important reasons why usin" an additional empty layer between the Hi"h and ow

Frequency layers is clever$

*hen you!re workin" on a separate layer to correct the ow Frequency data, you!re not messin"

up the eistin" piels on the ow Frequency layer. -ou can always either erase your mistakes or

hide them with a ayer %ark and not rely on the History ;anel states. 'his "ood habit may save

you a lot of time in the lon" run. #fter you!ve evened out the shadow and color transitions, you can apply :aussian blur to this

workin" layer to soften your own brush strokes and make the colors blend with the rest of the

ima"e even better. 'his is what #leksey does, and have tried it a few times already 4 works like

ma"icA /ach ima"e will require a different piel


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*hile the 'hreshold slider is at its minimum position, move the


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61 7on8t try to retouch the entire face with *ust one roun( of Frequency Separation1

Set up Hi"h and ow Frequency layers as many times as you need to solve problems in your current

retouch. personally do at least 9= rounds of Frequency Separation, and also &od"e 8urn the

problems that remain.


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#leksey su""ests that the best results can be achieved when you create custom Hi"h and ow Frequency

layers (3ust like he showed us earlier) for each part of the face that needs doctorin". -our


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8urnin". Sometimes it makes sense to soften lar"e shadows with &od"in" first and then only retouch skin

teture on the Hi"h Frequency layer.

t!s always different because every ima"e is unique. 8ut it will definitely help to know and practice both

techniques, so that you can easier determine which one will solve the problems you stumble upon better.

5 typically use the FS technique for color chan"es and &od"e 8urn for luminance chan"es. f you try

to make drastic luminance chan"es with FS, find that it can reduce teture as your new tones will blend

with the li"ht or dark tone of the Hi"h Frequency layer. &od"in" 8urnin", on the other hand, willdarken or li"hten both the hi"h and low frequency data, thus avoid this issue,6 says %ichael

*olos+ynowic+.

'hat!s all for today. am sure there are many more additional tricks that can be used with the Frequency

Separation technique, so if you know any 4 please share with us in the commentsA

Frequency Separation Technique

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