Photoshop allows for changing an image from its original, called source, mode to a different, or target, mode. The end use of the image determines the correct mode; for example, printing an image requires a different mode than for screen display. To change a color mode in Photoshop, follow these steps.
 Difficulty: Moderately Easy
Instructions
 1

Make all edits of the image in its original color mode. For digital camera images and scanner images, this mode is usually Red/Green/Blue or RGB. Drum scanner images are usually Cyan/Magenta/Yellow/Black or CMYK. Editing prior to changing the color mode will be easier and preserve more image data.

 2

Save a backup copy of the image which includes all layers before converting. Click "Save As" under "File" on the Photoshop menu bar. Type a new name for the image in the dialog box, navigate to the folder where the new file will reside and click "Save." The new file will appear on the screen.

 3

Open the Layers window by selecting "Window" on the menu bar and click "Show Layers" on the PC or "Layers" on the Mac. Flatten the image layers by choosing "Flatten Image" on the "Layers" palette pull-out, which looks like a right arrow on the upper right corner. The image layers should be flattened to ensure the blending color layers will not change when the color mode is changed. Also, some color modes do not support layers, and the layers will automatically be flattened when the color mode change is made. Complete all edits to the layers before doing this, as flattening the layers cannot be undone.

 4

Choose "Image" on the menu bar and then select "Mode." Select the desired mode from the submenu. RGB and CMYK are used for color printing. Other modes are bitmap, used for electronic images; grayscale, which is shades of black and white; and indexed, which is used for multimedia web graphics. A dimmed mode indicates that the mode cannot be used on that image.