All language subtitles for 12_Transversal_and_axial_chromatic_aberration

in this lesson

we're gonna learn about

the two types of chromatic aberration

and how we can apply them here in nuke

so at this point

we are almost through the lens

and we are now hitting the sensor

so let's take a look at why chromatic aberration

happens and well

let's first look at what it is

so here we have a very wide angle shot

and with wide angle lenses

chromatic aberration is usually going to be present

now it's going to be present more towards the edges

or on the edges of Infocus objects

so if I zoom in here on the right

you'll notice that every single

object is surrounded by a purple and a green line

and this is chromatic aberration

because again

the different colors have different wavelengths

so they move or refract through the lens differently

so this type of chromatic aberration is the most common

it's called transversal or lateral chromatic aberration

and it happens when light is hitting the edge of a lens

and gets bent improperly

so here we have an illustration of transversal or

lateral chromatic aberration

and as the light is going through the lens

you can see here that the blue

green and red wavelengths are beginning to be separated

and this happens more and more

the further away from the center it is

so this is usually either a

purple and green fringing

or a red and cyan fringing

and this occurs in almost every single lens

although some lenses

deal with it a little bit better than others

now this is transversal

so this is the

probably the most common

type of chromatic aberration that you're familiar with

there is another type of chromatic aberration called

axial or longitudinal

we can see this a little bit inside of this image

and this appears

usually when we have something very close

very in focus against an out of focus background

and this usually appears as a purple fringe

around an in focus object

and this is actually a rather interesting thing

uh our eyes and the

digital camera sensors we work with

are most sensitive to green light

and so when the focus motor or the focus

tends to um

get in focus

we focus on the green channel first

and that sometimes leaves

the red and blue channel slightly out of focus

so if we jump back to our illustrations here

we can see axial or longitudinal problems

or chromatic aberration happen

because the wavelengths would

or are focusing on the same plane

however they are focusing at different distances

through the sensor

so this happens only on in focus objects

and for the most part lenses

uh can fix this

or if you're paying attention while you're shooting

just slightly changing the focus will

uh tend to bring these closer together

and fix that edge fringing issue

so now let's jump in

and you can take a look at a few different ways

we can apply these

so let's jump into our project

and since these are close to the sensor

uh we'll add them in last

and to do a transversal

chromatic aberation

it's pretty simple

there's a few different ways we can do it

I'm gonna show you one of my normal ways of doing it

and then a slightly more refined way

so one of the easiest ways to do this is to drop in

two shuffle notes

so I'm just gonna shuffle one

shuffle two

and they're both going to be plugged into the same

input our original image

and now what we're doing is we need to separate

our channels and then

transform one of them differently

and then merge them together

so let's say we want to expand

the green channel

so let's go into Shuffle 2

and this will be our

RB channels

so we wanna turn green to black

and then shuffle 1 will be

our green channel

and we wanna turn

red and blue to black

okay so here we have our green channel

and our red and blue channel separated

so now if we merge these together

oops we hit m

and merge these together with an ad mode or A plus

we're gonna get the original image

now what we can do is we

can transform the green channel

and change it

and slightly

offset it from the red

and blue channels

now to see this

we're gonna have to zoom in quite a bit

because we want this to be a subtle effect

so we just need to increase or decrease the scale

now if we increase it by point 1

we're gonna get a very extreme

chromatic aberration

there's probably

not a lens on

earth that uh

messes up our colors this badly

so this is the

can only be a

processing error

error on the terms of

someone else

so let's dial this down

about 100 or 1,000 magnitudes of difference

so let's do a scale

difference of point zero

zero one and now

what we're gonna

get is a very subtle

green and purple chromatic aberration now again

this is going to happen

more on the edges

of our frame

so as we can see here

we can almost

see it right here

but in the center of our frame

we can't see it at all

so we can bump this up a few more

are you again

this is another

effect you need to be

really careful with

I see many people

overdoing this

and pretty much

making chromatic

aberration the movie

and we really want this to be a

subtle effect

even this right here is a little

bit too strong

you can definitely see it

and you're definitely noticing there is a

shift happening that is uh

beyond normal

so I'm gonna bump this back down to maybe point 2

believe that

was giving us a good value

what you want is to create a little

bit more contrast on your edges

and just create a little

bit more color

inside of your shot

so here we can

see we've got a little

bit of green

and a little

bit of purple

fringing okay

so this is looking pretty good as it is

now let's say

you want to do

red and blue fringing well

all you need to do is

switch these channels over

so let's do

red on the left

and then green on the right

and so now the red

and the cyan

channels will be

offset from each other

so in other words

the red and the

green and blue

now of course

we want to update this

so this is our

GB channels

and this is our

red channel

so this is a uh

fast way of doing it in a pinch

if we want a slightly

um more accurate way

we can actually

use God race

so I'm gonna move these over here

and let's just disconnect them for now

and let's hit tab

and drop in

our God rays

now what this does

is it takes the

current image

and then whatever we

apply to it

or whatever transform we apply

it does um a

few copies and then

blends between them

so this is actually a nice way to

get a soft chromatic aberration

so if we wanna begin with

our green one

let's drop down to

RGB and let's

isolate the green

and let's scale this up

a little bit

again it's very

easy to go overboard

so let's start

at a very low

value now again

we might need to increase this

until we see it

there we go

and we might wanna

pull that back a little

and as you can see

this gives us a slightly softer chromatic aberration

and it is more of an

additive mode

you can see

it's very subtle

uh even around the edges

so this is a nice way

and a and a

very node uh

not intensive way

of giving us

this nice chromatic aberration

and we can actually do this multiple times

if we wanna say let's

let's do the

red channel

instead of the green channel

so we have an

outer fringe of red

and let's say

we want a heavier

inner fringe of blue

we can add another God rays

and this time

just change

the blue channel

let's go back to our RGB

switch it over to blue

and now let's just scale it down

a little bit

so let's say

maybe point

nine nine okay

and now we have a

very subtle

but very nice looking

red to yellow

and then purple to blue

chromatic aberration

so as you can see

using these different techniques

you can create a lot of different variations

for these transversal

chromatic aberrations

so play around with these again uh

when we first add them

it's gonna be fun to overdrive these but again

this is needs to be a subtle effect or it's really

uh going to begin breaking uh your cop

so to add a

uh the other kind the axial

we just need to essentially find out what is in focus

and then blur

the red and blue channels of whatever is in focus

now since we already have an alpha channel in here

let's take a look at this

okay alpha channel

uh looks pretty good

we've got some clouds in here

that's a little strange

uh let's take a look at that

oh let's take a look at that in a second

for now we can add in an axial

chromatic aberration by just mimicking nature

so if nature blurs just the

um red and blue channels

we can do the same

so let's turn off the green channel

and just introduce a little bit of a

red blue blur

and you can see we begin to create that purple

fringing around our object

now of course

this can quickly get into 70s photo territory

so we again need to be careful with this

and this does have a tendency to turn highlights or

HDR areas pink

which is not exactly a great thing

currently we are just blurring the entire spectrum

so instead of blurring everything

let's just blur the edges of our alpha

so I'm just gonna drop in a

let's say uh

detect edges node

alright let's grab an edge detect node

and let's plug this in first

so we can uh

get the edges of our alpha channel

and this is gonna give us the edges of our RGB

switch this over to alpha

and it should give us the edges to our alpha

however we still have our clouds in here

and we still have some highlights in here

that's a rather odd

so let's find out where we're adding those in

because I think that's probably not supposed to be

so here is our alpha

let's dial it down just so we can see if there's any

bumps in it

so to speak

let's go down

our flares are not adding it

I have a feeling we're

adding it right here where our diffraction is

so right now we're modifying the alpha channel

which we almost never wanna do when doing

RGB operations

so let's go to our two

our two diffraction merges

and just disable outputting the alpha channel

and we need to do that on both of these

and now our alpha channel is back to its pristine state

okay so now our edge detect should correctly grab

the alpha channel

there we go

and now all we need to do is blur

the alpha channel

alright so it's blur based off of that

and now we can see we only

have that fringing

we actually need to

instead of connecting our

blur into this

we need to connect its mask port

so that we only have fringing around the edges

so now our highlights

are maintaining their current

um beautiful status

and our edges

now have this slight

slight axial

chromatic aberration going on

this is easier to see up here

near the top

just have a little bit of that purple fringing

that is common

uh with that system

now the axial

chromatic aberration

as I said earlier

is really only going to be seen if

you're very close to a subject

and you're very sharp in focus

and the focus cannot

um or the depth of field

or the depth of focus is so

razor thin that the different channels can actually

separate from each other

so in this case

we're actually

not gonna have a lot of

axial aberration

so we can go back and bump that down

but it is an important

aberration to keep in mind

uh uh because it definitely can

add credence and realism

to things like macro shots and

uh smaller images that we want to

add a little bit of that

uh axial chromatic aberration into

okay great so

try different channels

uh see what happens if you add

chromatic aberration with uh

yellow and purple or

uh blue and um

blue and yellow

and see what these different looks

uh look like

because each lens will create sort of

a unique chromatic aberration

so in this lesson

we took a quick look at how we can create both

the transversal aberration

which is aberration where the color spectrums

spread out along the sensor

and the axial

chromatic aberration

where the color spectrum actually spreads out

into the sensor

so let's close out our talks on

optical collaborations

and real world camera effects

by going into the sensor

and taking a look at film grain

in the next lesson