Adobe Photoshop CS4 - Manual (Page 119)

112 USING PHOTOSHOP CS4
Color fundamentals
Last updated 1/10/2010
Although its palette of colors is limited, indexed color can reduce file size yet maintain the visual quality needed for
multimedia presentations, web pages, and the like. Limited editing is available in this mode. For extensive editing, you
should convert temporarily to RGB mode. Indexed color files can be saved in Photoshop, BMP, DICOM (Digital
Imaging and Communications in Medicine), GIF, Photoshop EPS, Large Document Format (PSB), PCX, Photoshop
PDF, Photoshop Raw, Photoshop 2.0, PICT, PNG, Targa®, or TIFF formats.
Multichannel mode
Multichannel mode images contain 256 levels of gray in each channel and are useful for specialized printing.
Multichannel mode images can be saved in Photoshop, Large Document Format (PSB), Photoshop 2.0, Photoshop
Raw, or Photoshop DCS 2.0 formats.
These guidelines apply when converting images to Multichannel mode:
• Layers are unsupported and therefore flattened.
• Color channels in the original image become spot color channels in the converted image.
• Converting a CMYK image to Multichannel mode creates cyan, magenta, yellow, and black spot channels.
• Converting an RGB image to Multichannel mode creates cyan, magenta, and yellow spot channels.
• Deleting a channel from an RGB, CMYK, or Lab image automatically converts the image to Multichannel mode,
flattening layers.
• To export a multichannel image, save it in Photoshop DCS 2.0 format.
Note: Indexed Color and 32-bit images cannot be converted to Multichannel mode.
Converting between color modes
Convert an image to another color mode
You can change an image from its original mode (source mode) to a different mode (target mode). When you choose
a different color mode for an image, you permanently change the color values in the image. For example, when you
convert an RGB image to CMYK mode, RGB color values outside the CMYK gamut (defined by the CMYK working
space setting in the Color Settings dialog box) are adjusted to fall within gamut. As a result, some image data may be
lost and can’t be recovered if you convert the image from CMYK back to RGB.
Before converting images, it’s best to do the following:
• Do as much editing as possible in the original image mode (usually RGB for images from most scanners or digital
cameras, or CMYK for images from traditional drum scanners or imported from a Scitex system).
• Save a backup copy before converting. Be sure to save a copy of your image that includes all layers so that you can
edit the original version of the image after the conversion.
• Flatten the file before converting it. The interaction of colors between layer blending modes changes when the
mode changes.
Note: In most cases, you’ll want to flatten a file before converting it. However, it isn't required and, in some cases, it
isn’t desirable (for example, when the file has vector text layers).
❖ Choose Image > Mode and the mode you want from the submenu. Modes not available for the active image appear
dimmed in the menu.