Graphics Programs Reference
In-Depth Information
In the following steps you will explore the channels in a sample file.
1.
Go to the topic's Downloads page at
www.sybex.com/go
Businesswoman.tif
, and open it in Photoshop.
2.
Select the Channels tab to bring it to the front of the Layers/Channels/
Paths panel group. Select the Red channel (see Figure 3.11).
FIGURe 3.11
Channels panel
3.
Press Cmd+4 to select the green channel. Press Cmd+5 to select the
blue channel. Observe how each channel's grayscale information is
slightly different (shown in Figure 3.9, earlier in this chapter).
not all file formats
support alpha
channels.
4.
Select the Alpha 1 channel. Alpha channels are additional optional
channels beyond the color channels. In this case the Alpha 1 channel is
a mask that hides the background (with black) and reveals the business-
woman in white. Shades of gray appear in her hair where the foreground
and background blend slightly.
My topic
Enhancing
architectural
Drawings and
Models
with
Photoshop
(Sybex,
2010) shows how
alpha channels
can be used in
photoshop to com-
posite photographs
with 3d computer-
generated imagery.
5.
Select the RGB composite channel. The RGB, Red, Green, and Blue
channels highlight in the Channels panel because the RGB channel
isn't really a channel in its own right. RGB is merely a convenient
switch that sends each color channel to its corresponding subpixels
in the monitor so you perceive the color image on screen.
6.
Toggle on the visibility of the Alpha 1 channel by selecting its eye icon
in the Channels panel. A transparent red mask indicates where the alpha
channel masks the color image (see Figure 3.12).
