In the lecture about selecting hair,
we've already seen a blending mode in action.
When you give a layer a blending mode, 
you will be able to look through that layer,
without lowering
the Opacity of that layer.
So a blending mode is like a filter.
It will to let some information through,
for example all the light colors from beneath,
and at the same time blocks other information,
for example all the dark colors from beneath.
For this reason,
blending modes are very powerful,
and will give results
that are not possible to get in another way.
Blending modes can roughly be categorized
in four groups:
blending modes
that make underlying layers lighter,
blending modes
that make underlying layers darker,
blending modes
that give underlying layers more contrast,
and blending modes
that change the color of the layers below.
In three lectures, the most used blending
modes will be discussed.
To see a blending mode in action,
we need two layers or more.
The blending mode will be applied
to the top layer.
The layer or layer's under it, are the ones
that the top layer will interact with.
I have opened:
'Mountains' and 'Stars'.
In the Mountains image, I would like to have
some stars in the sky.
I will borrow the stars from the Stars image.
I drag the Stars image on the Mountains image.
I go to Mode, and choose
the 'Lighten only' blending mode.
Now I have stars in the sky.
So how does Lighten only work?
The Lighten only blending mode makes a comparison:
which layer has the lightest color?
Is it the layer with the blending mode,
or a layer below it?
For each pixel, this comparison is made.
The lightest pixel wins, and will be shown.
I only want the stars,
so I will remove the light mountains
at the bottom, using a layer mask.
I right-click on the Stars layer,
and choose: 'Add Layer mask'.
I choose a white mask,
and I press Enter.
To hide the mountains,
I will paint with black.
I press 'B' to select the brush, and in
the Tool Options I choose a hard brush.
I increase the size to about 400.
Now I paint away the light mountains.
If I hide and show the top layer,
I see only the stars are now added.
I will lower the Opacity a bit,
to get a more subtle effect.
Now we will look at the opposite
of Lighten only: Darken only.
We have already seen this blending mode
in action, in the lecture about selecting hair.
I have opened:
'Amsterdam', 'Clouds', and 'Birds'.
I would like to place some clouds in the sky.
I drag the 'Clouds' image over,
and drag the clouds a bit up.
Now I go to Mode,
and choose: 'Darken only'.
With Darken only, only the darkest pixels
will be shown.
That's why I see the clouds;
the clouds are darker than the bright sky.
Under the sky, I see the buildings, because
the buildings are darker than the clouds.
Let's optimize the result a bit.
To prevent that the clouds interact
with the buildings,
I will make a selection of the sky.
I hide the top layer,
and select the bottom layer.
I click on the Fuzzy select tool.
Now I click on the lightest area in the sky,
and drag the 'Threshold' to about 120.
Now that I have a selection, I right-click
on the top layer, and choose: 'Add Layer Mask'.
I click on: 'Selection', and press Enter.
I press Ctrl-D to deselect,
and click on the eye.
I can still see a bit of white in the trees.
To reveal the sky in the trees,
I select my brush,
and set the size to about 60.
I press 'X' to reverse black to white.
I paint in my layer mask to reveal the sky.
I will now create a new layer from what
is visible at this moment, like a snapshot.
I do this, by right-clicking on the top layer,
and choose: 'New from visible'.
I have now added a flattened version
of my document, in one layer.
I will brighten this new layer.
I press Ctrl-L to open Levels,
and drag the middle slider to the left.
I also would like
to put some birds in the sky.
I drag 'Birds' over,
and move them up in the sky.
I want to see the birds,
and hide the grey.
I will start by setting the layer
to 'Darken only'.
Because almost everything on the Birds layer
is darker than the sky underneath,
only the Birds layer is visible.
To change this, I open Levels.
I will brighten the image
with the mid-tone slider,
until the grey background
gets lighter than the sky beneath.
Now only the birds
are darker than the background.
Next we will look at 'Screen' and 'Multiply'.
Like 'Lighten only' and 'Darken only', 
'Screen' and 'Multiply' are opposites.
I drag the Girl image over.
I will place the girl layer
partially over the dark mountains.
If I set the girl layer on 'Lighten only',
I will see only the lightest pixels,
which means, only part of the Girl image,
and only a part of the Mountains image.
But what if I want to see
both images completely?
Under 'Lighten only',
I select: 'Screen'.
'Screen' can be compared
to using two separate slide projectors,
who are both projecting
on the same screen.
One projector shows the mountains,
and the other projector shows the girl.
The images overlap,
so we get a slightly lighter result,
but both images are now visible,
which is what we want.
Now let's look at a practical example
for 'Screen', and go to: 'Lens_flare'.
I would like to add this lens flare
to the Girl image, to give it a sunny effect.
I drag it over.
For adding the stars,
we used 'Lighten only'.
If we use 'Lighten only'
for the lens flare,
we see, we are not getting the result
we are looking for.
This is because
there is no 'real' blending going on.
The way to get the actual 'light'
from the flare,
is to use the 'double slide projector technique',
provided by the 'Screen' mode.
Screen can also be used
to lighten the image itself.
I hide the flare,
and make a duplicate of the girl.
I set the duplicate on: 'Screen'.
With 'Opacity' I can lower the light
from the 'second projector'.
The opposite of 'Screen', is 'Multiply'.
For 'Screen', we had the comparison
of having two projectors,
With 'Multiply' we are back to one projector,
showing both images at the same time.
You could compare it to a 'light table',
where you lay two transparent sheets
on top of each other.
The second sheet
will make the result darker.
Let's have a look.
I have opened: 'Rails'.
Let's say I want an orange circle,
and I want to see the background
through the orange circle.
For this, we will need
the 'light table' effect.
I create a new layer.
To draw a circle,
I select the Ellipse select tool.
I start dragging,
and then I add the Shift key.
To adjust its size, I drag a corner or side,
and add the Shift key.
To position the circle,
I drag in the middle of the circle.
Now I open the color panel,
and select orange.
I fill the selection
by pressing Alt-Backspace.
I press Ctrl-D to deselect.
In the layers panel,
I choose: 'Multiply'.
Under 'Multiply' we have 'Burn'.
I have opened: 'Building'.
Burn is a variation of Multiply,
and gives a more dramatic effect.
It gives more contrast and saturation,
providing a 'cinematic' look.
In the next lecture,
we will look at the 'Contrast' group.
