All language subtitles for 1B_02

Before starting to explore the post-processing
chain, it is important to draw the distinction

between the scene referred and display referred
formats. so imagine you have just rendered your

shiny new lighting setup in Blender and what
you see on screen actually has two layers to it.

a deeper layer that we cannot see directly on our
screens is the data of our render engine, of Cycles,

the unbounded light intensity is stored in the
32-bit format and then the second layer is what

get transferred to our display or we actually see
on screen. that is called a display referred image.

to better get the difference between these
two types of image and how it all ties with

the post-processing chain, let's first save our
image as PNG or jpeg or any other 8-bit format

with 8-bit holding a display referred data in
this case, so let's go with any 8-bit format

like jpeg, PNG, Tiff, by saving the image in one
of these formats we will effectively bake the

color management within the image pixels, it
will be the depth of the deeper data layer,

the layer that held all the high dynamic
range intensities of light in your scene.

actually it's pretty easy to prove that there
is some range of intensities underneath what is

displayed, let's open our color management tab
to get access to exposure slider, it will come

in handy in just a moment, now if we sample the
hottest spot in our render probably generated

by the sun lamp via right clicking on it you
will see that there are intensities there that

go well beyond one, for example the red channel is
as bright as 35 units and these units are not the

display brightnesses that go from black to white,
these values are the unbounded brightnesses of

the actual 3D scene, technically it can go from
zero all the way to infinity and beyond while

our miserable Rec 709 displays are limited to go
from 0 to 1 in terms of intensity and that's it.

now watch the hot spot, it's a really hot bunch of
pixels indeed, now if we start killing the exposure

notice that the hotspot is still hot! why is it
so?! :) because it had the higher intensities right

of the start, the intensity that we have sampled
before and if we sample it now it won't change,

the red channel will still peak around the 35
to 40 units depending on where you sample it.

so even after the reduction of the exposure in
the color management tab, the super bright scene

referred light values still result in super bright
pixels on display after it gets transferred to

our display via the color management system.
the CM letters here stand for color managed.

so that's why this part doesn't
want to get dimmed even when we

reduce the exposure, because it holds an
enormous punch in the scene referred realm.

all right! so what what would be the right way to
save the entire dynamic range of this image then?

there is a special type of image format meant for
storing such data, the scene referred data, glorious

open exr for example, this format can store 32-bit
data with floating point accuracy or half floating

point accuracy if you want to save on the file
size, it has a bunch of very potent compression

codecs that we won't go into right now, but the the
main thing about it (let's keep it short) is that

it can save the whole range of the scene referred
unbounded image data or light data in other words.

and you guessed it, we will need this 32-bit
image fidelity in post processing, if we're

gonna save the file just like we
did and post process it afterwards.

to drive it home let's compare 8-bit display
referral and 32-bit scene referred formats in

Blender compositor and see how it all works. so
I'm gonna open the new blend file, toggle the

compositor right away, N to remove the right
two shelf check Use Nodes, what else... maybe for

convenience's sake I'll create two windows, the
bottom one will be the image editor where we will

preview our compositing chain, now the resolution
should be set to 1920 by 1080 pixels just like our

original scene, it's the best practice to make
sure these two things align perfectly, now Ctrl

Shift clicking on the render layer to create the
viewer node and then opening the viewer node in

the image editor and this is our basic setup for
post processing, now instead of using the render

layers as if we have just rendered something, let's
actually load our 8-bit image via the image node.

so here we have two of these guys, the PNG
and the exr, let's start with the PNG one, so I'm

connecting its image output to the viewer and
you tell me what did go wrong with the image?

can you see this dusty screen effect like the
image got flattened? that's because the filmic

view transform was applied twice technically, first
we baked the display transform right into an 8-bit

image, a PNG in our case and then we applied the
display transform for the second time in this

new blender scene, hence the weird flattening of the
contrast, on top of that we have lost all the wide

dynamic range on saving in the PNG format. now
the litmus test! :) the reduction of the exposure.

remember we had the area of the higher intensities
that spanned across the wide dynamic range and

went all the way to 35 and above? yeah, forget
about it, it was clipped to 1 on saving the

PNG file, it was clipped to display. sadly for us
3D lighting artists the scene referred lighting

data is no more. we technically can do nothing about
it and to make it even more sad it will definitely

affect our post processing options as well. let's
demonstrate it by throwing in the glare node.

the way the glare effect works in Blender is that
it detects the very hot scene referred pixels with

the intensities of 5, 10, 15, you name it and then it
blooms these higher intensity pixels, there are no

more such pixels there they were all trashed,
so there is no more glare as simple as that.

thankfully we have also saved the 32-bit open exr
with the unbounded light values, the scene referred

values, which is important, so let's see how it
behaves instead. let us switch our image to the EXR

and obviously the first thing everyone gonna do
is sample the bright pixels and... woo! we've got our

high intensities back :) [sings: hello brightness my
old frieeeend] ...it's good to see them back!

you can sample any bright area to just
double check if everything is all right,

so that is the result that corresponds 100%
to the Blender render that we made in the

previous tutorial, that is the the wide range of
lighting values intact, we can prove it by our

exposure litmus test, the super bright bunch
of pixels generated by the lens flare... it is

still there. now technically this 32-bit image file
should hold all the intensities we need for post

processing, the full image data intact and so we
can go to building our universal post processing

chain, but first for the sake of completing our
little experiment let's drop in the glare node.

back into compositor, Shift A, Filter, Glare. now it
should absolutely catch those outstanding scene

referred RGB pixels that go above the threshold
of 1 in terms of their intensity and so that

is the major difference between saving the image
before post-processing it in the 8-Bit format such

as PNG, jpeg or Tiff or utilizing one of the scene
referred formats such as open exr which is 32-bit

by default. the scene referred image formats
were created for the computer graphics work,

for storing the light values required for post
processing, so that naturally should be our choice

and incidentally to double down on this point
when we hit F12 to render stuff out in Blender

we render it internally precisely in the 32-bit
scene referred format (just to clarify things).

here I want to pause really quickly and talk about
the alternative backdrop preview options. some

people like to preview the Blender compositor
output not in the separate window such as the

image editor at the bottom of the screen
but right within the Blender compositor one.

in order to see our stuff right there we
just need to check the backdrop button at

the top of the UI then this little preview
can be resized with help of the V or alt V

shortcuts or panned around while holding
Alt and using the middle mouse button,

what we see in the backdrop is actually the output
of the viewer node, so if you don't see anything

you just need to add the viewer first. if it feels
more convenient for you to preview the compositing

chain right in this viewport, I respect your choice
obviously :) don't forget about the viewer though.

my personal preference is quite fluid and
it depends on my mood and on the project,

fluctuates quite a bit, but I think my current vibe
would dictate me to use the image editor instead.

now technically nothing prevents us from jumping
straight into building the post-processing chain.