10 Hue/Saturation
Hue/Saturation
is the tool that lets you tweak the colour of your image and how much
colour there is.
You
can use Hue adjustment for special effects purposes, like this
Shrek-a-like, (Hue +180, Saturation +50).
That's
a very limited sort of application though. More practical uses are
far less dramatic. Here's a before and after, adding 5% saturation.
All its done is lift the blondness of her hair and made her cheeks a
touch rosier.
It's a small difference,
quite hard to see at this scale but it makes a very noticeable
improvement.
As
a rule of thumb, I expect to need 1-2% more saturation for every 10%
of Shadow/Highlight adjustment because lightening shadows leaves then
washed out.
While
reducing saturation is rarely necessary, there is one very specific
time when it comes in handy. It's a great tool for removing something
called a Chromatic Aberration. Chromatic Aberrations are those
(usually) blue halo effects along the edges when dark objects are
photographed against bright backgrounds (or vice versa), especially
at long range. I'll show you how in a later chapter.
One
of the nice things about Photoshop's Hue/Saturation tool is that it
lets you adjust individual colours separately. You can pick red,
green and blue (The three primary colours for screens) or cyan,
yellow and magenta (the three colours of ink for printing). You can
mix and match them too.
In
the original flower picture, the petals were so white I didn't dare
brighten the image and the green was already vivid and vibrant but
the purple was almost black.
By
adjusting only the magenta channel with the Hue/Saturation tool,
increasing lightness and saturation by about 10% each, I got the
centre of the flower the way you see it. The purple tips of the
petals came up nicely too.
By
far the most likely reason for needing the Hue/Saturation tool is
because you've lightened a picture taken in dark conditions. That
happens to me a lot because, this being Britain, the sun is mostly
not there or, on the rare occasions it shows up, it's in the wrong
place. Remember the dragonfly?
The
green is too vivid and there is a purple tint to the abdomen. No
problem: we can adjust green and magenta separately with the
Hue/Saturation tool.
First,
I've darkened the green by setting the Lightness slider to -70% in
the green channel. It doesn't change it as much as you'd expect
because most greenery is actually more yellow than green (strange but
true).
Second,
in the magenta channel, I set saturation to -70% to fade out the
purple haze on the abdomen.
The
green is restored to its original levels and the purple is gone but
the dragonfly is no longer a silhouette. I'm not done with this image
yet. Watch out for it in the chapter on sharpening.
A
lot of photography happens in an environment with mood lighting.
Artificial lights really mess with colours. Your brain does an
amazing job of interpreting true colours under these conditions but
cameras haven't got brains.
This
example was taken in a dimly lit (halogen bulbs) coffee shop. Holly
was 8 metres from the camera too, making the available light even
less useful.
The
bright patch at the tip of her nose is a helpful indicator of where
to start correcting colour. Highlights like that are almost always
supposed to be white. This one is yellow. So let's reduce the yellow
(a lot).
Amazingly,
I had to take the yellow saturation slider down about 70% to get to
here, but the background still has yellow in it so there was
obviously way too much of it.
And,
having taken out all that yellow, some will get put back because I've
added about 10% to the Master saturation slider to get the brightness
of the colours back up.
It's
still not a brilliant image, but it's far closer to what the eye sees
under those lighting conditions.
So,
with one tool we can lighten, darken, intensify or wash out any
colour you want. We can even change one colour into another. Handy.