- [Instructor] Curves are perhaps
my favorite color adjustment control.
When first looking at them,
they may not seem to do all that much for you,
but they're actually an incredibly flexible and precise tool
for adjusting the appearance of your images.
They work the same way in every application.
Learn them once and you can use them everywhere.
The way I learned how curves work
is by somebody drawing a line
to indicate the brightness of a pixel
coming in and going out from the effect.
You can use curves controls
to adjust individual color channels, too,
but let's just start with the overall luminance.
What's rarely clear in a curve control
is that it's kind of a graph,
with the horizontal axis
representing the level of the original image,
or let's just speak about an individual pixel,
and the vertical axis
representing the resulting output level
once an adjustment has been made.
You'll notice the default set-up has a line
going neatly from not percent to 100%,
so no changes are made.
I'm saying 100% here rather than a particular level
because it doesn't matter what color system you're using,
what bit depth, or what your maximum levels are.
A curve control will always work the same way.
Imagine the line is a kind of mirror,
reflecting a beam of light.
Here's a pixel that's 50% bright.
The light comes in at 50%, hits the line,
and comes out also at 50%.
Look what happens when I drag the line,
automatically creating a control point
to change the relationship between the input and the output.
Now, a pixel that's 50% bright coming into the adjustment
comes out at only 25%.
The beauty of a curve control
is that it adjusts all the other values, too,
creating a more natural-looking adjustment
than you'd achieve by only adjusting the pixels
at that level of brightness.
You can adjust the ends of the line, too,
reducing the overall contrast or increasing it.
These adjustments are most clear
if you view the result in a waveform,
where you can see the pixel values
stretching or compressing.
Lifting or lowering the middle of the line
brightens or darkens midtone pixels,
which has a dramatic effect for the viewer.
The same principle applies
to working with individual color channels,
with one important difference.
When adjusting luminance,
you're working with a scale that has bright at one end
and dark at the other.
When adjusting colors,
one end of the scale has more of the color,
while the other end of the scale
has the secondary color that matches it.
In the case of red, for example,
the other end of the scale is cyan,
for green it's magenta, and for blue it's yellow.
This makes curves particularly useful
for making adjustments to colors
at particular levels in the image,
though it can require a little experimentation and practice
to get natural-looking results.