All language subtitles for 05_Lens_distortion

in this lesson

we're gonna learn about lens distortion

and field curvature

so here's our camera diagram again

we are now inside the filter and inside the lens hood

so now we're hitting the actual glass

elements of the lens

and there's a lot of different things happening here

so we're gonna begin by looking at

lens distortion and field curvature

now lens distortion happens because there are so many

elements and so many things we want to fix

uh we need to somewhat bend the image

and you'll notice we are going against a flat sensor

so lens distortion

shows itself usually in bent lines

so I wanna open up an image from a wide angle lens

and you can see

that the lines here that are straight in real life

are bent to an almost absurd angle

now this was not shot in some sort of

uh fairy land

this is actually just the natural um result

of trying to remove as many aberrations as possible

and so this is more common with wider angle lenses

but even uh

zoom lenses or even high focal length lenses

will show a little bit of lens distortion

now in our case

we're at a somewhat unique

um position in that we do

not have any lens distortion to go off of

since this is a CG image

it does not have any natural lens distortion in it

if we were adding this or modifying a C

G or excuse me

a real life clip

we would need to calculate

the lens distortion happening

and then match that inside of our composite

now on our case

we're just going to add a lens distortion

so I'm gonna hit tab and drop in a lens distortion node

and drop this in

now parts of this node only work inside of Nuke X

which I'm currently running

so uh we'll take a look at those here in a second

but for now

we can add the different types of distortion

to our image

so there's two main types

well three main types

I should say

first is pin cushion

where the corners of our image are pulled out

uh in sort of a pin cushion manner

so let me scale this down so we can see

exactly what is happening to our frame

and let me turn back on the black outside

so I'm gonna disable my crop up here

so we can see what is actually happening

oh that is not actually fixing that

so right before our lens distortion

just gonna add a transform node

that's still giving us the outside

so let's try to scale us down in the transform node

and we're probably doing a little

bit too heavy of a lens distortion

so let's pull that back

okay so here is a pin cushion distortion

you can see that the corners are being pulled out

now the opposite of the pin cushion is a barrel

distortion where

the image begin taking on the shape of a barrel

you'll notice the corners are being pulled in

and lens distortion always happens or has the most

effect on the corners or edges of an image

you'll notice that this pixel is displaced much

much further than pixels in the center of our image

now the third type of distortion is a

mustache distortion

and it's gonna be a little bit difficult to see

but if you just imagine

the curvature of a fancy mustache

it is a complex distortion with the mix of barrel

and pincushing like properties

now since we do not have a source to go off of

I'm just gonna remove that

transform there

so that we can see this again

uh we can uh sort of make up a lens distortion

although I really do not like uh

going by this method as it's uh a little bit random for

uh my preferences

so uh inside of your footage folder

we're gonna have a piece of footage that are shot on

one of our lenses

so I'm just gonna import this

and this is just a piece of grid

paper that we shot with a camera lens

this is one of the many ways of analyzing a lens

so I'm gonna plug the lens distortion node into this

and again if you do not have Nuke X

this is not going to work

um but we can jump over to grid analysis

and change our grid type to thin line

analyze the grid

and it is going to give us the distortion values

so we'll let uh new tick for a second

and here we can see the original grid

you can see it is distorted

uh with a slight what looks like a barrel distortion

and then the undistorted

makes all of these lines straight again

and you might be asking

why are we trying to undistort this random image

and the reason we're doing that is

to get natural values for a lens distortion

now of course

if you have your live action footage

or if you have your real footage

analyze that footage to get your lens distortion values

but since we don't

I'm just gonna use this uh

random grid image we had laying around

plug this back into our original source

and uncheck und distort

so we are now

and if I turn off my grid overlay here

we are now distorting our image

with this lens distortion

now let's double check

and our let's see our

our image has grown leaps and bounds

so let's actually add a few crop nodes in here to

cut that down

let's see where that would end up

so just going to crop this oops

not cross talk it

I'm going to crop it down

just so we're not

unnecessarily

adding a lot of information

before our lens stored there

alright so here is with our new crop

and we might need to increase the size of this

a little bit

trying to see if this lens distortion

it is um okay

so without the crop

one thing you'll need to be careful about whenever

adding lens distortions

is if you lose information from the edge of the frame

so you'll notice here that if we zoom in

we are losing about

I don't know

5 to 6 pixels on the edges of our frames

and this is noticeable because

the last line of pixels will be stretched out

now unfortunately

with this uh

kind of a mechanical looking image

it's gonna be difficult to see

but you can tell here that these pixels are

all repeats of the exact same pixel

and so we need to be careful whenever we

use a lens distortion

so if we add a crop

we can see that our

uh new distortion is much smaller

than the actual image

so what we're gonna need to do is actually scale

up the image

uh if we want to keep it within these boundaries

now an important note

if you are matching

any kind of other element

to a different element that has lens distortion

the workflow is

you und distort everything

so you calculate the distortion on everything

und distort it and then

comp everything together

and then finally

add the distortion again

and what that is going to do is it's going to give you

uh something akin

to the original uh frame

that we started with but again

since we're working with a CG source

we really only need to distort this

the importance of lens distortion is that

straight lines are

not actually straight when they're captured by a camera

and although it's unconscious

our brain knows this

so even if you have a completely CG image

we need to add a little bit of lens distortion

now to get around this curvature

I'm just gonna add in a transform

and scale this up a little bit

now I know you're thinking

scaling up oh

what are we doing

uh we're gonna

ruin our image

but again in this case

we have a CG image

which needs to be softened regardless

and scaling it up a little

bit is actually going to soften it

just enough

so that it's not too noticeable alright

so if we go back to

uh 1 x zoom

let's take a look at this

with and without

our lens distortion

so you can see here

our lens distortion is bending the image

in a way that actually

our eyes do find pleasing

and once this begins

moving throughout our shot

the sort of dynamic way

those straight lines

are going to bend

and shift inside of our frame

is gonna feel

much more realistic to us than

seeing a completely

un distorted image

so that is how we can

add lens distortion now

I actually wanted to go into field curvature in this

lesson as well

but as you can see here

we're running

out of time

so let's actually

cover field

uh curvature in

the next lesson

so in this lesson

we Learned about lens distortion

which is just a natural

characterist

characteristic

whenever we bend light

this is most

commonly or most

extensively seen

inside of a

wide angle lens

as we can see here

but even uh

at any focal length

we still need to

add this into

our composites

and if it is inside of

our natural footage

we can either

understort it to

add in more

elements naturally

or if we're working with

uh CG render

we need to add in this lens distortion

so that the lines

curve in a more pleasing manner