Digital Media I Susan M. Raymond West High School
Lesson 14 – Image Modes
In this tutorial, you will: Change an RGB Image to Grayscale Mode Explore the Distinguishing Characteristics of Photoshop’s Four Color Modes . Photoshop allows you to select one of the several different image types, or modes, to work with . The modes vary in complexity from black and white to color for commercial printing on a press . It is important to understand the similarities and differences in image types to best utilize Photoshop for your specific purposes . Using the correct color mode can minimize your file size and processing time, and is essential for obtaining quality output . Each color mode appears in the Mode submenu of the Image menu . Two characteristics differentiate between Photoshop’s image modes: the number of channels, and the bit depth of each channel . All of Photoshop’s modes, from the simplest to the most complex, differ only in the number of channels and the pixel depth per channel . The complexity and file size of an image increases with the number of channels and pixel depth . In order to view Photoshop’s image modes, you must have an image open
. Find and open the Dog.psd file in your folder . Choose Image, Mode . Observe the image mode choices in the submenu
. You will change this image of the dog to the Grayscale mode . Choose Grayscale from the Mode submenu . An alert dialog box appears, indicating that changing to a grayscale will permanently discard the image’s color information
. Click on OK . The image is now made up of grayscale pixels . Although you could return the image to RGB color, the image’s original red color would not reappear The image would be made up of grayscale pixels that are defined as a combination of red, green, and blue Choose File, Close Click on the No button . Photoshop has four modes that contain color information . The four modes include: Indexed Color, RGB Color, CMYK Color, and Lab Color . The Indexed Color mode contains one channel, much like the Grayscale and Duotone modes . The bit depth can be set from 1 to 8 bits . However, each pixel can be a color instead of a shade of gray . A color table is used to establish which colors are available . The RGB Color mode has three 8-bit channels . Each color component can use 256 shades . The three channels combine to make a 24-bit image, resulting in 16.7 million colors . Since each color channel has the same amount of information as a grayscale or indexed color image, the file size is three times as large . RGB mode is most commonly used for images that will be distributed electronically and viewed on a monitor, such as images for the Web . In addition, you’ll most likely work in RGB mode for editing and painting . For printing purposes, it’s necessary to convert RGB images into subtractive primary colors: cyan, magenta, and yellow . In theory, cyan, magenta, and yellow added together form black . Although color printers use cyan, magenta, yellow, and black inks, most inexpensive printer drivers are optimized for printing RGB images, so you shouldn’t convert from RGB to CMYK in Photoshop . However, for commercial printing and when using more expensive printers that use the PostScript printing language, you should convert the image to CMYK . This process is often called color separating, because for commercial printing, the four ink colors are printed separately on a press
Cyan Magenta
Finished Product
Yellow Black . The Centre Internationale D’Eclairage, an international organization for establishing color measurement standards, developed Lab Color in 1931 . The Lab Model defines colors mathematically, is device-independent, and is consistent color regardless of the device producing the color . Lab Color is therefore unlike RGB, which is used for monitors and scanners, and CMYK, which is used for printing . The Lab Color mode, like RGB, uses three 8-bit channels to represent color . L is the luminance component, ranging from black to white . A is a chromatic component ranging from green to red . B is a chromatic component ranging from blue to yellow Points to Remember:
. Bitmap and Grayscale are the two modes that do not contain color information in Photoshop . The Duotone mode allows for two, three, or four inks to be used in the PostScript printing process to reproduce levels of gray . Photoshop has four modes that contain color information: Indexed Color, RGB Color, CMYK Color, and Lab Color