- [Instructor] Let's look at exposure control
in order to set up a lighting scheme
that is basically accurate.
We've got a single point light here in this office scene.
If I select that and go to the modified panel,
we'll see in the intensity color attenuation rollout
it has an intensity of 8,000 candelas.
Let's switch this to lumens that's a lot more intuitive.
We see that we have over 100,000 lumens.
That is not a physically plausible value.
If this were, let's say, a fluorescent tube,
it might have an intensity of maybe 3,000
not 100,000.
So we want to bring this into something
more physically plausible.
Let's set the lumens to 3,000 and press enter.
So with a value of 3,000 lumens
we have an extremely dim shot.
While we're at it, we should change the color temperature
if we want this to be a fluorescent tube,
maybe we'll set the Kelvin value.
We'll click on the radio button
for the Kelvin value and set that to 4,800 degrees Kelvin.
And it's a slightly orange rendering.
So we've got this light set up
so that it more or less matches
a real world lighting instrument.
But as we see again, we have this very dim, very dark shot.
So we're going to fix this by going into the exposure control.
If you recall when we first created this photometric light,
we were prompted, do we want to turn on exposure control?
And I opted to not turn on exposure control at that time
'cause we want to set the exposure control
up very specifically,
and the default settings are not really very helpful.
But let's do it by hand manually and do it correctly.
Exposure control is found in the rendering menu.
Go to rendering, and it's actually inside the environment
and effects dialogue, so you could choose environment
or you could choose exposure control,
it will actually take you to exactly the same place.
At the top we have the common parameters
where we could do things like a sign and environment map
to our background.
I'm going to collapse that,
and focus on the exposure control rollout.
And it's disabled right now.
We see no exposure control chosen in the pull down list.
We can click on that list and see
that there are numerous choices for exposure control.
The only one of these that you're likely to ever
want to use is physical camera exposure control.
As the name indicates it acts like a real camera.
So select that,
and immediately we see that our scene
got a little bit brighter.
There's a switch up here to deactivate it if you want,
we want to make sure that's on.
We come to the actual parameters.
Up at the top, we have a checkbox labeled
use physical camera controls if available,
and that's on by default.
What that's going to do is allow you to set
each physical camera in your scene
to have different exposure.
So maybe, I've got one camera that's a close up
on something and it needs to have different exposure values
than some camera that maybe has a long shot.
Well, okay, that's great.
But it's on by default here
and that's not really what we want.
The thing is that we're looking
through a perspective view here
and the perspective view has no exposure controls.
So we don't want to use this switch
and we want to make sure that any cameras
that we create later are all going to have the same exposure.
And to do that, we'll need to turn this switch off.
Once we do that,
then we're able to adjust the global exposure value here.
If this switch is on,
then ironically this even though it's not grayed out,
has no effect on the cameras.
Okay, so use physical camera controls if available
should be off, and then we can adjust the exposure value.
This exposure value or EV works just like f-stops
on a camera.
So if you're are familiar with a real camera
it'll have f-stops to control the amount of light coming in,
and they'll have numbers like 1.4, 2.8, 5.6 and so on.
Well, this works exactly the same way
except it doesn't have those bizarre numbers,
it just works in whole integers
which is a lot easier to work with.
Each whole integer will increase or decrease the sensitivity
by a factor of two.
So it's actually exponential.
In other words,
if we bring the exposure down from six to five,
reducing it by one stop, we're doubling the amount of light
coming into the sensor.
If we bring it down to four,
we're doubling the amount of light coming in again.
All right, so let's bring this down to, let's say two,
and we get a slightly overexposed shot.
But we're not done,
we also want to adjust the white balance.
Right now it's set to the default of 6,500K or D65.
And we get a slightly orange rendering
because our Kelvin value is 4,800 on our light.
If we want to white balance the camera
so that it recognizes that orange light as if it were white,
then we would set the color temperature for the camera
or the exposure to be the same as that of the light.
We could select temperature here
and bring this down to 4,800 degrees and press enter.
And now we've white balanced the camera
so that we get a neutral white in our rendering.
Then we come down to image control.
And this is by far the trickiest part of all of this.
This is applying a contrast curve to the rendered image
or in this case, the viewport.
Now that's kind of a legacy or a old school workflow.
Nowadays, we don't actually want to apply a contrast curve
at render time,
because that contrast curve is going to be permanent.
It's going to get burned in to the pixel values
of our rendering.
It's a much better practice to not adjust the contrast curve
at this point, but rather to render out a linear
or a neutral none tone mapped image,
and then adjust its contrast in an editing program,
some kind of image editing or compositing application.
What we want in this case
and really mostly in all cases nowadays,
is to merely bring the image into the correct exposure range
and white balance.
We don't want to apply any tone mapping at this stage.
But unfortunately this image control
is set up by default to apply a contrast curve.
And additionally beyond that, we have this graph over here
that's put to indicate the shape of that contrast curve,
and that graph is extremely misleading.
I want you to just completely ignore it and pretend
it doesn't exist.
And if I had my way, it would be removed or updated
because the scale of the graph is completely wrong here.
What we want in the image control settings
is a very specific set of values,
which will give us a linear response
with no adjustment of contrast.
So the values for that would be highlights of one,
midtones of one, and shadows of zero.
We don't want to actually crush the blacks.
So with these settings, highlights one, midtones one,
shadows zero, it looks like this graph is clipping off.
But again, that's extremely misleading.
The graph should actually go up like twice
as much as it is now in order to show the full range,
but it doesn't.
So, these are the values we want.
With these values we're not introducing some contrast curve
and we're just rendering out a purely linear response.
So having done that we can see that it's pretty overexposed.
We can increase the exposure value
essentially reducing the sensitivity.
So let's bring that up to a value of four.
And it looks a little bit dim in our viewport
but actually if we render this in Arnold
or some other renderer that has a global illumination,
it'll be a little bit brighter
because there'll be bounce light going around.
So let's try that.
I've got active shade already set up from Arnold,
so click on active shade on the main toolbar,
the icon which is a teapot with a little triangle on it.
And that'll take just a moment to initialize,
and we can see that indeed it is a little bit brighter
than the viewport, because again, we have bounce light
and we also have specular highlights or reflections here.
You also may notice that we don't see the actual light
in our active shade rendering.
We have an icon in our viewport,
but we don't see the source of light
here in our Arnold rendering.
And that's because we're using a point light
down here in the shape/area shadows roll out.
We have the shape of the light
and it's currently set to point, and a point has no size.
It's infinitesimally small, it's a zero dimensional object.
And so since it takes up no space in the actual 3D world,
it can't actually render because it doesn't have a size.
Of course, in the viewport we have an icon
or a gizmo representing that light
and that's for our convenience,
so we'll be able to actually select something.
But that doesn't necessarily the actual scale
or volume of the light.
All right.
So that's the basics of how to set up exposure control.