|
Photo shown with channel window displaying the color
channels that make up the image.
Left column shows default color channel. Right column
shows the same channels with preferences set to show channels in color.
Alpha one is a channel containing the selection of
the child's outline. This selection will be available at a later time.
Sample showing the main image view when only the Red
channel is selected. The selection will remain and affect all channels
when the RGB channel is activated.
Photos © Tom
Thomson Photography. Used with permission.
|
|
In order to fully understand saving masks, we must go where I will
have to drag some of you kicking and screaming – channels. I spoke
in the first part of this tutorial
about the mystique surrounding masks in the computer graphics world,
but the fear and lack of understanding about channels seems to be greater
than with masks. We are going to put that to rest once and for all right
here.
Channels are simply the view of an image separated into color components.
If you are working with images for the Web, you will be working in RGB
mode, or Red, Green and Blue. These three colors are used to produce
the images you see on your screen.
Channels simply take the image and divide the information on a color
basis. See the sample at the left of a photo, plus the channels that
make up this image.
Channels are represented as grayscale images. To help understand how
the channels work, I have included a comparative view of the color channels.
In the left column, the channels are represented as grayscale images,
the default and recommended setting. The right column was produced in
PhotoShop by choosing File>Preferences>Display and Cursors>Color
Channels in Color. Note: You cannot have both color and grayscale
displayed as I have here – this is a composite image I created
for this tutorial. I am also not recommending that you change your preferences
for showing the color channels in color. The grayscale is much easier
to work with. I included this simply to present a visual image of what
is happening on the color channels.
Note how the grayscale images represent strong color with light gray.
It may help to think of the channel images as a negative view of the
color. In this image, there is a great deal of red, and very little
blue.
So what can the channels do for us? They can make selection easier
and bad photos can often be saved by applying corrective effects to
individual layers, but that is not the focus for this tutorial. Our
interest in channels has to do with the Alpha 1 channel shown here,
which you may note right away, is reflecting the selection in shown
in the photo.
After saying we were really not interested in the easy selection that
channels can offer, I feel duty bound to tell you that this selection
was almost instantly accomplished by using the magic wand selection
with only the red channel active – one day I will do a tutorial
on selection and special effects using channels.
The second sample at the left shows the red channel active. The original
photo is unchanged, as shows with the RGB thumbnail, but since the red
channel is active, all other information is hidden. As soon as you click
back to the RGB setting, the full color photo will be displayed on the
work area. It should be very clear from this view how selecting the
outline of the child would be much easier with this view rather than
with the full color view. Any selections made will apply to the active
channel. To have it affect all color channels, simply activate the RGB
channel.
When you have a selection created in your document, you can either
save the selection to disk, or save it with the document. I will not
get into great detail here, since each program handles this feature
in a different way.  But
it is important to understand that when a selection is saved, it is
always represented as a channel. We will use this feature a lot over
the next few pages. At the right I have included a sample of the Alpha
1 selection from above. Alpha 2 is the same selection with a feathered
edge to show the grayscale representation in a channel. These mask looking
representations do not affect the appearance of the document at all
in this state. They are simply selections saved for future use. Do not
confuse a selection channel with a layer mask.
That really is all you need to know about channels for this article
(that wasn't so bad was it?). With that background, we can move on to
specific programs and then to your new beginning using channels and
masks to make your work faster forever.
|
