Channels
Explained: Why Photoshop is Color Blind.
Note: This tutorial is intended for beginners.
It explains some basics, but it does get
pretty deep into Photoshops innards here
and there. If you believe anything is
incorrect here, then please email
me, I'm always learning myself. Also keep
in mind things are being extremely simplified
because the details of Photoshop's innards
scare me.
This
tutorial is intended to give a quick overview
of how Photoshop sees and interprets Channels,
as well an an in-depth explanation of
what Channels actually are.
It
can be assumed that most people reading
this know that Photoshop is a bitmap program,
and that bitmap pictures are composed
of a whole pile of little dots called
pixels. But, what many Photoshop users
don't know is that while they are creating
ultra colorful pieces of art, photoshop
is, in a way, color blind.
What
does this mean? Well, to explain that,
we need to talk about Color Modes and
Color Separation and Channels.
Color
Modes:
Remember physics class? Remember learning
about the light spectrum? The Human Eye
can see only a small band of visible light
among microwaves, radiowaves, etc, etc?
Well, just because it's virtual doesn't
mean physics stops working. Photoshop
uses a small section of the visible light
to display its colors, and different sections
of the spectrum, called Gamuts, are labeled
as different Color Modes. The most common
Color Mode for print pieces (files outputed
through a printer) is CMYK. This means
that every color in the Gamut that makes
up all the files' colors are mixed from
Cyan, Magenta, Yellow,
or blacK. Almost all printers use
this four color process.
Sidenote: RGB
(Red, Green, Blue) is the Color Mode
for the web and anything that is only
viewed on a monitor. RGB printers do
exist, but they cost a boatload of money.
It is interesting to note that the RGB
Gamut is larger than the CMYK Gamut,
meaning that it includes more of the
visible spectrum and therefor, more
colors. Soooo, if you start working
on a picture in RGB, there's a good
chance your colors may not translate
correctly to CMYK, because it won't
exist in that Gamut. This is where you
start getting into the wonderful land
of Color Correction, which is poopy,
so I won't talk about it.
Color
Separation:
Don't worry, I'm getting to the black
and white part, and to the tutorial
part. If you ever contract a professional
printer than they will take your file
and pull apart all the colors, each
into their own color plate. This is
called Color Separation. Printers take
a file and all the Cyan colors they
put on one plate, all the Yellow colors
they put on another plate and so forth.
Each plate is in grayscale, with light
areas signifying where that color ink
is placed on the page, and darker signifying
where it is omitted. To sum this up,
the Printer drops ink over the page
four times, one for each plate, and
the colors are mixed magically on the
paper!
Channels:
Now, behind the scenes, Photoshop is
working the same way. If you are working
in RGB mode, for example, Photoshop
separates the colors out into three
plates, called Channels in Photoshop;
a red channel, a green channel, and
a blue channel. If you open the channel
pallete you can see these three channels,
all represented in black and white.
And to the user's eye, Photoshop magically
mixes the colors on screen.
Side
note: Just because there are 3 channels
by default for RGB Color Mode, and 4 for
CMYK, doesn't mean that you are only limited
to having 3 channels. Additional channels
don't necessarily alter the color in the
image though, and instead are used for
other purposes. For example, channels
are an excellent way to store selections.
Here's
a handy experiment to show off this
process.
Start
with a normal RGB image and fill it with
black. Now, go to windows>show channels
if the channels palette isn't already
open. Click on just the red channel and
use the paintbrush to draw a white circle
on it. While you paint in white on the
Red channel, you can see the RGB channel
update with a red circle
Click
on the Green Channel and draw another
pure white circle, this one partially
overlapping old one. The red circle will
disappear when you first click on the
green channel, since red is invisible
on that channel, but if you click just
on the little "eyeball" icon
box next to the red channel you can view
it. Don't click on the channel itself
though, or you'll be painting on the wrong
channel.
Click
on the RGB channel, which displays all
channels at once, and you can see where
the green and red circle overlap there
is Yellow.
If
you feel creative, draw on the blue channel
with white,
overlapping both other circles and you
can mix a pure white in the center!
Anyway.
To sum all this up in one, over simplified
sentence, A Photoshop file is not just
a collection of pixels. A Photoshop file
is an arrangement of pixel data, each
holding an address as to placement in
the file and a value of grayness for each
and every channel in it's color mode.
Learn how to use channels to your advantage.
Just like with everything in Photoshop
you can select, manipulate, distort and
tweak them to tailor to your needs. Try
running filters on just one channel of
a photo, it's fun!
