Page 57 - Adobe Photoshop and Dreamviewer 2021

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
exercise. (You will use channels extensively in later projects.)
Every image has one channel for each component color. Each channel
contains the information for the amount of that component color in
any given pixel. An RGB image has three channels: Red, Green, and
Blue (right top). A CMYK image has four channels: Cyan, Magenta,
Yellow, and Black (right bottom).

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 You can save a Quick Mask channel as a permanent Alpha
value determines the degree of transparency of a pixel. In channel by dragging the Quick Mask channel onto the New
other words, a 50% value in the Alpha channel means that Channel button at the bottom of the panel. This adds a
area of the image will be 50% transparent. channel named “Quick Mask copy,” which remains even if
you exit Quick Mask mode. You can then double-click the
When working in Quick Mask mode, a temporary Quick Mask Alpha channel name in the panel to rename it, as we did in
channel stores the degree of transparency based on the the following image (naming the channel “Lion Head”).
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 default masked areas.

Clicking the Color swatch opens a
Quick Masks are useful when you need to work with a Color Picker, where you can change
temporary selection, or if you are still defi ning the exact the color of the Quick Mask overlay.
selection area. As long as you stay in Quick Mask mode, the You can also use the Opacity fi eld to change the transparency
temporary Alpha channel remains in the Channels panel of the overlay (the default is 50%). Keep in mind that these
(listed as “Quick Mask”). If you return to Standard mode, the settings only affect the appearance of the mask in Photoshop;
Quick Mask disappears from the window and the panel. the density of the selection is not affected by changing the
overlay opacity.

Project 1: Composite Movie Ad 69