So welcome for our computer graphics lecture.

So on Tuesday, we finalized the section on ray tracing.

And I already introduced a bit what

we are going to speak about next.

And essentially, that's a complete formalization

of light transport in virtual worlds.

And you know that ray tracing is a method.

And I described several ways to simulate light propagation

in scenes.

So we were speaking about reflection, for instance,

which is quite simple to simulate.

But there are other more complicated effects.

And the nice thing is that it's quite simple,

or not too difficult, to really describe all these effects.

So most of the effects we are interested in

in a simple equation, which is called the rendering equation.

So the entire illumination problem,

and thus a core of computer graphics,

can be described by a single equation that fits into a line.

And so it's a good basis to describe all methods

in ray tracing, for instance, and stuff like that.

And this is what we will look into.

But we will start with radiometry.

That means we will have a look at how light is described.

So which physical units do we have

to describe the emission of a single point of a surface?

A single point emits light into various directions.

So emitted light depends on the direction, for instance.

Of course, it also depends on the point on the surface.

Now the question is, if this point emits light

into this direction, how much light arrives

on the other side, and so forth.

And we will start with a description

of these physical units.

So that's radiometry.

Then I will further detail the concept of BRDFs,

so of these functions that describe how incident light

is reflected.

And we will then look at the rendering equation.

So that brings all this together,

describes the entire light transport

in a scene in a simple equation.

And then we will look at or see why ray tracing is nothing

than a simple numeric integration method

for the rendering equation.

Once we have this equation, we can simply

derive that ray tracing is a very simple way

to compute that rendering equation numerically.

OK, so today we will speak about radiometry.

That means how do we physically measure light?