|The Power of Ten
|An introduction to the concept of viewing every image as having ten channels.
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"Every file has ten channels." Dan Margulis, Professional Photoshop.
I remember, years ago, looking at the channels palette for the first
time and asking myself, "What possible use would anyone have for this
Today, I don't touch a single pixel without looking over the channels first.
Whether RGB, LAB, or CMYK, I do the channel tour; Cmd/Ctrl 1, 2, 3, and sometimes 4.
One idea that has transformed how I work in Photoshop is that every
file has ten channels. RGBLABCMYK. That's what I call The Power of Ten.
Photographers, working with light, typically know their way around RGB
and have trouble with CMYK. Printers, working with ink, deal with CMYK
and usually shy away from RGB. Neither one tends to use LAB very often,
assuming they even know what it is.
The purpose of this tutorial is to show how the ten channels are more alike
than you may think. RGB is simply the flip side of CMYK, and passes
through LAB to get there. This is actually how Photoshop converts from
RGB to CMYK and vice versa. It uses LAB as the crossover from one to
Attached is a chart which illustrates what I'm talking about.
The columns are the three color modes; RGB, LAB, CMYK.
The first three rows are the opponent color pairs; Red to Cyan, Green
to Magenta, Blue to Yellow. The last row is the contrast channels;
Lightness in LAB and blacK in CMYK. Although the opponent color
channels have a very clear relationship to each other, the contrast
channels don't. They're the odd man out and lend themselves to some
very unique and powerful editing techniques.
Notice that LAB has only two color channels, the A & B. Even so,
the three opponent pairs are still there. When the A & B channels
are equal and positive, the color is Red. When they're equal and
negative, the color is Cyan.
Here's a little exercise to help get acquainted with the idea of ten
channels. Make three copies of any image. Convert one copy to RGB, one to LAB, and the last one to CMYK. Now open the channels palette and start
comparing the various channels from the three images. In the discussion thread for this tutorial I've attached a Photoshop Action which will set this up for you.
You should notice right away that the channels which are opponents look
almost the same. Red resembles Cyan, Green resembles Magenta, Blue
The LAB channels are a little tougher to comprehend, they just look
like subtle gray blurs. The key to understanding what they represent is
that warm colors (magenta, yellow, red) are light gray and cool colors
(green, blue, cyan) are dark gray.
Contrast and Color.
Another thing to consider about the ten channels is the unique ways
they handle contrast and color. In RGB, each channel is equally
responsible for both. In CMYK, much of the responsibility for contrast
gets shifted to the blacK channel. In LAB, contrast and color are
almost completely separated into the L and A&B channels
This suggests certain strategies for image manipulation based on color
mode, keeping in mind that there will always be exceptions.
As noted, in RGB each channel deals with contrast and color equally. In
practice however, this is not always the case. It has been observed
that certain "types" of contrast tend to gravitate towards specific
channels. In general it breaks down like this: Red > Contrast, Green
> Detail, Blue > Noise.
Doing a luminosity blend using the Red channel can greatly improve
contrast in sky scenes. Since detail lives mostly in the Green channel,
a very serviceable B&W can be extracted from many RGB composites by
simply discarding the Red and Blue channels. To clean up noise, one can
apply various noise reduction filters to the blue channel without the
usual lose of detail one gets when targeting the composite image.
Since CMYK is the "flip side" of RGB, one will notice that the Magenta
channel holds the most detail and noise tends to land in the Yellow
channel. This means many of the same techniques one can use in RGB
still work. But it's the blacK channel that really offers some very
powerful moves which are extremely difficult to duplicate when working
My favorite CMYK specific maneuvers deal with sharpening. One can use
much higher settings and achieve quite wonderful results targeting only
the blacK channel. For an extra sharpening boost I'll apply USM to the
"unwanted" color as well. The "unwanted" color is the lightest of the
CMYK channels. In a product shot featuring something which is
predominantly Red, the Cyan channel will be the lightest. Applying the
same USM settings to the Cyan and blacK channels will add some real
snap to said image.
Enhancing shadows is one place where CMYK can't be beat. A curve to the
K is often all it takes to really bring out the detail in the darker
tones of an image.
LAB takes the separation of contrast and color a step further. The L
channel has all the detail, while the A&B channels deal solely with
color. But since there can also be contrast in color, and color can
affect detail, we can't really say that contrast and color are
The most fundamental LAB technique is the ability to increase color
variation. The typical example takes a drab landscape shot and applies
a curves adjustment to the A&B channels. The result is a much more
vibrant, eye-catching image. This type of enhancement is almost
impossible to duplicate in color modes where contrast and color live as
When faced with a particularly difficult need for cloning, try
converting to LAB and cloning just the L channel first. Then follow-up
with a simple patch to replace color. In addition, Sharpening and
Shadow/Highlight are much more powerful when applied directly to the L
A very common retouch is to colorize a B&W image. LAB outshines the
other two color modes here as well. One can add color by painting
directly into the A&B channels. Since all detail lives in the L
channel, it's impossible to harm detail in any way.
Dealing with contrast and color separately can be extremely powerful,
and these ideas are just a few of the ways in which they may be
manipulated. As noted before, the more one thinks in ten channels, the
more their treasures will be revealed.
Detailed descriptions of techniques using channels is beyond the scope
of this tutorial. But if you read any of my posts you'll find examples of
the ways in which I incorporate these concepts into my workflow.
I hope this post has provided a little food for thought. If you'd like
to discuss any of these ideas further simply start a thread somewhere
and I'm sure to jump in.