curves - natalia taffarel
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8/17/2019 Curves - Natalia Taffarel
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CurvesNATALIA TAFFAREL·SEXTA, 15 DE JANEIRO DE 2016
In order to understand curves we need to understand color in the way that
photoshop does.
Additive color theory
EVERYTHING in an image is made o ! colors " RE# " GREEN " $%&E
Each circle is painted on an individual' independent layer " The Red has the RG$ values set
to ())"*"*' the Green has the RG$ values set to * " ()) " *' and the $lue has the RG$
values set to *"*"()) +,rimaries- ,ure RE#' pure GREEN' pure $%&E " Each layer /lending mode is set to screen " 0ver a $lac1 $G
The interaction /etween two primaries create secondaries Cyan' 2agenta'
Yellow
The center creates pure white " ()) " ()) " ())
The variation o luminosity o each creates all the range o visi/le colors.
3e also need to ta1e into account the relationship between tones and
we can see that in the RGB color wheel
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3e can see ,rimaries and the secondaries as their complimentary " RE# and cyan " GREEN
and magenta " $%&E and yellow.
Every color that we see in a screen is ormed with only these ! colors.
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These apparent gradients are actually created with gradients o the ! ,rimaries set to screen
/lending mode on /lac1' creating the illusion o the whole range o hues +4**5saturation'4**5 luminosity o course' we need all the ranges o %um6sat to have all the colors and I
will address that urther on.
Every single one o the millions o tones we perceive in an image are
created /y the primary !
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This image was created illing each independent layer with the primary colors " The Red has
the RG$ values set to ())"*"*' the Green has the RG$ values set to * " ()) " *' and the $lue
has the RG$ values set to *"*"()) +,rimaries- ,ure RE#' pure GREEN' pure $%&E " Each
layer /lending mode is set to screen " 0ver a $lac1 $G " Then each channel luminosity wasused as a mas1 o each o the layers to duplicate the appearance o the image without
needing to have the image.
3hen I separate the ! layers it loo1s li1e this-
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Even 3hat it7s perceived as %uminosity is color
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To create white we need ()) "())"()) To create $lac1 we need *"*"* To create Grey we
need 4(8"4(8"4(8
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3hy is this important to understand curves9
Curves work with the 3 channels to modiy the image. Even when
you thin1' you7re only wor1ing with light.
How9
:or e;ample' when you pull the curve up to /righten up the image li1e
this-
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3hat you7re actually doing is pulling up the ! individual channels up at
the same time
%i1e this-
Lets take a look at the Curves and the different parts
The curve can /e edited rom 4< individual points' the main ones /eing )-
/lac1 point' shadows' mid"tones' highlights and white point.
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You can also use the 0N I2=GE tool in the curve to alter an speciic range
within the image
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In the curve we can also ind ! eyedroppers that can /e used to select the
! main points- whites' mids and /lac1 point respectively.
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These can /e used or automatic color6contrast corrections /ecause when
we select the dar1est6lightest point o the image' the curve will
automatically ma1e the whites pure white and the /lac1s pure /lac1'
getting rid o any tint or color contamination.
There7s a tool you can use to accurately ind the dar1est6lightest points o
your image- Threshold
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,ushing the threshold slider to the let' it will ma1e the whole image
white' e;cept or the dar1est point
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,ushing the threshold slider to the right' it will ma1e the whole image
/lac1' e;cept or the lightest point
3e can use it as a reerence when using the curves eyedropper to select
the white6/lac1 points more eiciently.
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The curves will automatically ma1e the necessary ad>ustments to the image' correcting the
tint.
$ut lets understand how to ma1e ad>ustments ourselves' rom simple
changes to more advance color grading.
%ets say you have red and you want the red to /e orange.
:irst' lets learn what red is
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=nd what orange is
?o the dierence /etween that red and that orange is 4(8 points o green.
Ta1e the curve' pull up the green rom the input * ta1e it to input 4(8 and
you get orange.
Input and output are how curves wor1.
Lets look at that into more detail:
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Initially' the tonal range o an image is represented with a straight
diagonal line over a graphic. 3hen wor1ing in RG$ the top right
represents lights while the /ottom right represents shadows.
Hori@ontal a;is represents the input values +the current values in theimage
The vertical a;is represents the output' the values ater you ad>ust them.
2oving the curve up increases the values and moving the curve down
decreases them
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The same happens with the color curves here7s a visual representation o
what happens when you move the curves.
=nd you can even see how it aects an image
In each o these e;amples the color curves were pulled up rom input 4(8 +midtowns or
the top6let triangle and pulled down rom input 4(8 or the /ottom right part.
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In each o these e;amples the color curves were pulled up rom input 4(8 +midtowns or
the top6let triangle and pulled down rom input 4(8 or the /ottom right part.
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In each o these e;amples the color curves were pulled up rom input 4(8 +midtowns orthe top6let triangle and pulled down rom input 4(8 or the /ottom right part.
&sing curves you can also change the saturation o colors not only the
hue6luminosity.
%ets go /ac1 to my red sAuare. I turned it orange /ut it7s too saturated
or' lets say' s1in"tones.
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This part is 1ind o logic' i you want white you need the ! tones in their
pure state ()) "())" ()) so i you want grey then you need 4(8"4(8"4(8
You had orange ())"4(8"*
You need that orange to /e /righter +closer to white- there or more even
in values' yet 1eeping the proportions so it7s still Borange
?omething more li1e ((* " 4D* " 4)* +=ppro;imately' this is not e;act' /ut
I7m sure it will wor1
?o RE# is starting in ()) " we need to go to the input white point +())
and pull it down to ((*
The GREEN was at 4(8 " ?o we go to the input 4(8 +mid"tones and move
them up to 4D*
The /lue was in * "?o we need to go to the input * +/lac1 point and pull it
up to 4)*
Result-
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?ee9 Told you it would wor1.
So do you need to use numbers or know these numbers to understand
curves9 No' not really. nowing the num/ers is gonna ma1e it e;act and
mathematical /ut you can also do it /y eye and use the color wheel as a /ase.
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3e only have ! Channels +RE#' GREEN' $%&E' there or i I want
YE%%03' there7s no yellow curve to move' I will need to remove /lue i I
want yellow. ?1in is yellow and red.
?o I I want to turn something grey into s1in"tones loo1ing tone I need topull down the /lue and add some red. ,ro/a/ly pretty dar1' so I add some
light using the RG$.
=lways starting rom the input o 4(8 /ecause it7s grey.
You can see this as you go without 1nowing any o the num/ers.
You do need to 1now your color wheel.
But… didn´t we just used another curve to do the skin-tones with the
even values and all that? YupF =nd that7s the /eauty o curves.
It also wor1sF #ieren7t curve' ?ame result
This last one has a mathematical /ase /ecause it was thought out rom
color num/ers' while the previous one is pure color 1nowledge Bwell i I
want to do s1inniness then I need red' yellow and light " $oth ways wor1
as long as the theory /ehind the thought process is correct.
%ets change more colors and orget the num/ers a /it.
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%ets go rom /lac1 to ?1intone " Evidently we start rom the input o *
now /ecause we are trying to change /lac1
=lso considering I7m starting rom /lac1 " Complete lac1 o color " * * * "
2y idea o putting the /lue down' does7t help me much.I need to pull the green up
3hen changing whites' again' I need to change the input rom where I7m
starting.
I can7t alter the midtowns or /lac1 point since that would7t change the
image at all.
Now I need to start rom the white point' ())"())"())I can7t add light /ecause it7s already the /rightest it can /e so I need to
reduce the tones' 1eeping the proportion.
3ell Now you 1now how to change whites and /lac1s and mitones.
Now that we 1now what happens to white' grey and /lac1' lets move on to
colors. =n image is regularly conormed /y neutral tones.
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In this visual everything that is not grey +lights and shadows is /lac1 and everything that ismidtown has /een illed with )*5 grey. = good way to select midtowns is to use Bcolor
range in the select menu' it has an option to select only midtones.
It7s also common that images have mostly even channels' usually within
the midtown range.
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This means the image will change +/e aected when ma1ing movements
on curves rom the midpoint +4(8 input value This is not always so' some
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times we have too dar16too light or too saturated parts and we need to
understand how the color curves wor1 then.
These colors were purposely chosen to have 4**5 sat6lum so they would create uneven
channels.
%ets see how the channels loo1 in these mostly pure tones.
RE#
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GREEN
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$%&E
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The part o the image with the pure colors is mostly e;treme +/lac1
orwhite in the channels" with little mid"tone
It is important to understand that since each color is mostly white or
/lac1 ' they will not /e aected /y a movement o a curve rom the middle
tone. $ecause o /eing mostly pure colors ' they will always have ()) o
one or two o the ! colors and * o the other one " so the channelsgenerally will /e almost /lac16white with little mid"tone range %oo1ing at
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channels will help us 1now rom where in the curve you need to ma1e the
moves. This is only necessary at irst' /ecause ater a while you get used to
literally seeing in channels and you no longer have to loo1 at them to
1now how they loo1 li1e. To understand this visually
I I apply a /lue curve rom the mid"tones it will only aect areas o the
image containing gray in the /lue channel
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?o' also' most o the image itsel
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=nother thing to ta1e into account is that' in an image' when we change
the colors rom the ends +white or /lac1 input we will /e changing the
apparent /rightness o the image and depth' so we have to 1eep that in
mind when ma1ing changes. Not only is will /e more /lue' /ut also
/righter. I we ma1e the changes rom the /lac1 or white point' the image
will gain or lose contrast as well. Lets see how we can use what we
have learnt to actually work on an image The sample image that I
7m using has a lot o redness around the eyes
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$ut i7s not really red' it7s more li1e pin1
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=nd I want that pin1' to /e orange. ?o starting rom the mid"tones
+remem/er our image had mostly grey tones in the channels I can ta1e
some /lue out and add a /it o green' then use a mas1 to constrain the
correction and' with this curve neutralise the Bredness without loosing
saturation and 1eeping the area with the original tonal variations. 3hen
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you use saturation or paint on an empty layer or any other correction that
implies one lat color' you lose naturality. 3ith curves' it7s a lot /etter.
The mas1 was created e;aggerating the pin1 with a saturation ad>ustment in con>unction with a /lac1 and white ad>ustment to enhance the dierence urther and then using
channels to e;tract it.
%i1e this you can do all sort o corrections' always ta1ing into account the
RG$ wheel or the relation /etween colors. 3ith curves you can also do
creative changes. Very popular e;amples /eing the split tones. ?ince
the human /rain is very 1een on complimentaries.
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$ut most o the times' we have a reerence in mind. ?ometimes is a clear
one' li1e another image. I7ve decided to use a non traditional reerence
that came up in my retouching group.
http-66www./i>ou;"components.c@6
The way to match reerences is to learn to see. &nderstand what to loo1
or in reerences. I the thought process is organi@ed then it should /e easy
and ast +ater years o doing it' o course The main issue is to 1now
where to loo1 and what to loo1 or. 2y /rain is already ully programmed
to thin1 in curve ormat' there or my mind immediately as1s a ew
Auestions. 4" How /road is the range /etween the highlights' lights'
midtones' shadows and /lac1 point9 How much contrast does the image
have? - In the case o this reerence! the contrast is "uite low! with the
e#ception o a ew highlight$ 4" The highlights- Have a tint9 3hich9 =re
they pure white or greyish9 " %he lights are deinitely not white &with the
e#ception o those ew highlights' and has a green tint or sure$ (" $lac1s
have a tint9 3hich9 =re they pure /lac19 Blacks are not even close to
being pure black! and have a lot o red$ !" 3hat happens in the
midtones9 Having little contrast and complementary colors in highlights
and shadows in this reerence generatesa neutralised appearance o
midtones. " ?aturation9 = %ot9 = %ittle9 3here9 In this case' there is not
much saturation in general while /oth %IGHT? and $%=C? are very
saturated. Result-
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easy and ast J
Everything you can do in photoshop' you can do with curves.
I´m sure it took me longer towrite this than it will take you
to understand it :) Now, go play with curves! Natalia
Tafarel