Color Modes and Channels in Adobe Creative Cloud
Several color modes are available for use in the Creative Cloud applications. When you start a new document in Photoshop and Illustrator, you can choose the color mode you want to work in. In fact, both Photoshop and Illustrator help you by letting you choose a color mode in the New Document dialog box.
The choice you make affects how colors are created. You can change the color mode later by choosing File→Document Color Mode in Illustrator or Image→Mode in Photoshop.
If you’re working with print, generally you use CMYK mode. If you’re working on files to be displayed on a monitor, RGB is the right choice.
RGB (Red, Green, Blue) is the color mode used for onscreen presentation, such as an image displayed on the web or a broadcast design for TV. Each color displayed onscreen has a certain level (between 0 percent and 100 percent) of red, green, and blue to create the color. In a Color panel, you can either use sliders to set the level in values, as shown in this figure, or enter a percentage into a text field (such as in CMYK Color mode).
Note the exclamation point on the Color panel, which is the Out of Gamut symbol. It indicates that this color wouldn’t reproduce correctly in CMYK mode. You can click the CMYK warning exclamation point to convert to a color that’s suitable for the CMYK gamut.
When you create a web page, the color is represented as a hexadecimal number, which starts with a pound sign (#) followed by three pairs of letters and numbers (A through F and 0 through 9) — the first pair for red, the second pair for green, and the last pair for blue.
The lowest value (the least amount of the color) in a hexadecimal number is 0 (zero), and the highest value (the greatest amount of the color) is F. For example, #000000 is black, #FFFFFF is white, #FF0000 is red, and #CCCCCC is light gray. To see what a particular hexadecimal color looks like, go to Visibone.
Working with CMYK
CMYK — Cyan, Magenta, Yellow, and Key (or Black) — is the standard color mode for print media, particularly in commercial printing such as what a service provider does.
The CMYK color scheme is based on pigment (a substance used as coloring) color separation, and it describes how light reflects off pigments. When you work with this color mode, you create black by adding the maximum values of cyan, magenta, and yellow all at one time. You can create different levels of gray by combining equal, but not maximum, amounts of cyan, magenta, and yellow.
White is simply the absence of all color. Many color printers now work by using the CMYK color model and can simulate almost any color by printing two colors very close to each other; however, some at-home desktop printer models made by Epson, Hewlett-Packard (HP), and Canon use their own color systems to print your work.
Saving in grayscale
You’ve seen a lot of grayscale images (color images displayed or printed in black and white) because the pictures in this book were printed in grayscale. Grayscale refers to the different shades of gray that can be used when printing using only black ink on a white page.
Halftone patterns are created when an image uses dots of varying diameter or when an image uses many small dots in the same area to simulate different shades of gray. Halftone patterns help simulate different color values by adding dots to simulate shadows and gradients between colors.
Looking at color channels
When you work with an image in Photoshop, the image has at least one (but typically more) color channel. A color channel stores information about a particular color in a selected image. For example, an RGB image has three color channels: one that handles the reds (R), one for handling green information (G), and the last for information about the blues (B). See this figure.
You can have, in addition to the three color channels, an alpha channel, which can hold the transparency information about a particular image. If you’re working with a file format that supports transparency, you can add and use the alpha channel to save alpha information. Some file formats that support transparency are .png, .tiff, .gif, .dcs, .eps, and the native .ai and .psd formats.
You can also use an alpha channel to save a selection. By choosing Select→Save Selection in Photoshop, you create an alpha channel with your selection saved to it. You can choose Select→Load Selection and choose the channel to reload your selection at any time.
In Photoshop, you can access the channels in your image by choosing Window→Channels. When the Channels panel opens, you can toggle the visibility of each icon by clicking the eye icon next to each channel.