Page 57 - CC2017_PS_Look_Inside

Understanding Channels
You need a bit of background about channels to understand what’s happening in the Quick Mask you will use in the next
PHOTOSHOP FOUNDATIONS Every image has one channel for each component color. Each channel
exercise. (You will use channels extensively in later projects.)

contains the information for the amount of that component color in
any given pixel. An RGB image has three channels: Red, Green, and Blue
(above right). A CMYK image has four channels: Cyan, Magenta, Yellow,
and Black (below right).

In RGB images, the three additive primaries can have a value of 0 (none of
that color) to 255 (full intensity of that color). Combining a value of 255
for each primary results in white; a value of 0 for each primary results in
black.
In CMYK images, the three subtractive primaries plus black are combined
in percentages from 0 (none of that color) to 100 (full intensity of that
color) to create the range of printable colors. Channels in a CMYK image
represent the printing plates or separations required to output the job.

Understanding Alpha Channels
An Alpha channel is a special type of channel in which the Channel button at the bottom of the Channels panel. This
value determines the degree of transparency of a pixel. In adds a channel named “Quick Mask copy,” which becomes
other words, a 50% value in the Alpha channel means that a permanent part of the file even if you exit Quick Mask
area of the image will be 50% transparent. mode. You can then double-click the Alpha channel name
in the panel to rename it, as we did in the following image
When working in Quick Mask mode, a temporary Quick (naming the channel “Baby Face”).
Mask channel stores the degree of transparency based on
the current selection. A semi-transparent red overlay shows
areas being masked (i.e., the areas that are not included in
the current selection).
Permanent Alpha channel
Temporary Quick Mask channel
New Channel button

You can change the appearance of an Alpha channel mask
by double-clicking a channel thumbnail in the Channels
panel. In the top half of the resulting dialog box, you can
change the overlay to show
selected areas instead of the
Quick Masks are useful when you need to work with a default masked areas.
temporary selection, or if you are still defining the exact
selection area. As long as you stay in Quick Mask mode, the Clicking the Color swatch opens a
temporary Alpha channel remains in the Channels panel Color Picker, where you can change
(listed as “Quick Mask”). If you return to Standard mode, the color of the Quick Mask overlay. You can also use the
the Quick Mask disappears from the window and the panel. Opacity field to change the transparency of the overlay (the
default is 50%). Keep in mind that these settings only affect
You can save a Quick Mask channel as a permanent Alpha the appearance of the mask in Photoshop; the density of the
channel by dragging the Quick Mask channel onto the New selection is not affected by changing the overlay opacity.

Project 1: Composite Movie Ad 67