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Photoshop and PSP Channels: What, When and Why?
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One image, four views. The image at the top left
is the "normal" view for a Web image, or one with the red,
green and blue channels combined. The top right image shows
a grayscale image containing only the red pixels. The lower left
image is green only pixels, and the lower right displays only
the blue pixels.
Photos © Tom
Thomson Photography.
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I have been meaning to return to the very basics of raster functions
that so many of you request, and this week I finally found my way
back. We have already looked at masks
and selections, plus layers.
Channels have the spotlight for this tutorial.
Print designers work with channels all the time, since the color
separation required for all printing is represented by channels. However,
for Web design, we have no need to use channels when we save our images.
We often ignore that channels even exist. In all honesty, if you never
crack open the channels palette, or in the case of Paint Shop Pro,
separate your document into channels, you can still produce highly
professional work.
However, there is a reason to open that palette. When you
separate your document into channels, you have just turned on your
fine tuning capability. Have you struggled with an image that seemed
to require both sharpening and blur? The answer may be as easy as
working in only one channel. Or sharpening the red channel, removing
noise from the green channel and applying a slight blur to the blue
channel. The is no filter or adjustment that can simulate what you
can do my manipulating individual channels.
And don't forget, channels are also used to hold our masks, which
is how any saved selection is represented. (See Masks
are Easy ... Really.)
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Red, green and blue separated on the left, and combined
to create the final image at the right. I lightened the red sample
here to make the eagle easier to see.
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What is a channel?
For this section of the discussion, we are going to talk only about
the color channels.
When we look at a colored image on our monitor, we are actually looking
at a combination of only three colors: red, green and blue. It is
a combination of the three colors that produces the millions of colors
we see. Look at the image at the left. I have broken an image into
the three color channels that make up the final picture at the right
of the image. When we are working with channels, the red, green and
blue are usually represented with a grayscale image, but I have used
the actual color here to illustrate the concept more clearly.
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100% of red, blue and green will result in a white
display.
Photoshop Channels palette with preferences set to
display color, rather than a default grayscale image for each channel.
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Red + green + blue = white. What?
Yup, 'tis true. You take 100% red color on a monitor, and add 100%
blue and then 100% green and you see white. Whole books are written
on why, and how it is opposite for color on paper. We don't need need
all that information to use channels for our Web work, though. We
just need to know that they combine to make white for RGB images.
Otherwise, the channels will make no sense. If channels have always
seemed to be backwards, you now have your answer.
Having trouble believing me? The lower image at the left is taken
with Photoshop set to show the channels in color (select Edit >
Preferences > Display and Cursors and check Display: Color Channels
in Color). The document is a one layer image with a white background
and the channels view shows the colors that are used to make the white
that you see.
Why is this important? Because if you want to reduce the effect of
a color in a channel, you have to make it darker – that is contrary
to our natural instincts. I just want to get you thinking the right
way (or is that the wrong way ... backwards ... adding color because
it is a subtractive model ... nah, you don't really want me to go
there). All that matters is that you understand that dark in a channel
translates into less of that color. Light in a channel means more
of that color.
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Default channel display is a grayscale image for
each channel. In this Paint Shop Pro generated channel split, the
top left image is the actual image.
Photos © Tom
Thomson Photography.
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Channel display
We have had our fun times with the colorful channels, but it is time
to get back to reality. Channels are most often displayed as a grayscale
image, since that is what they are. When we were viewing the channels
in color, we were simply looking at the grayscale image in color.
Look closely at the separated eagle image above and you will see that
in each channel, only one color is represented. The variations that
lets us see shapes are simply shades of the color.
At the left, I have included a set of images from Paint Shop Pro.
The image at the top left is split into channels – see the channel
name in the title bar for each window. Notice how dark the green and
blue channel images are. That means that there is a small amount of
blue and green in this image.
Not surprisingly, there is a lot of red in this image - the red channel
is quite light, except for the land mass and the tree. If 100% of
red, blue and green makes white, it only makes sense that 0% makes
black. We have a near black land mass and tree, so the all the channels
contain little color in that area.
With that introduction, roll up your sleeves and check out how you
can work with Photoshop and Paintshop Pro.
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 Wendy
Peck is a working Web designer and writer living in NW Ontario, Canada.
http://wpeck.com
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Next page
Photoshop and PSP Channels Tutorial Index
Photoshop and PSP Channels: What, When and Why?
Photoshop Channel Basics
Splitting Channels in Photoshop
Paint Shop Pro Channel Basics
Enhance Images and Create Special Effects
 
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