Adobe 23101335 User Guide - Page 127
Converting between color modes (Photoshop), Converting between bit depths
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ADOBE PHOTOSHOP 6.0 117 User Guide Converting between bit depths A 16-bit-per-channel image provides finer distinctions in color, but it can have twice the file size of an 8-bit-per-channel image. In addition, only the following Photoshop tools and commands are available for 16-bit-per-channel images: • The marquee, lasso, crop, measure, zoom, hand, pen, eyedropper, history brush, slice, color sampler, and clone stamp tools, as well as the pen and shape tools (for drawing work paths only). • The Duplicate, Feather, Modify, Levels, Auto Levels, Auto Contrast, Curves, Histogram, Hue/Saturation, Brightness/Contrast, Color Balance, Equalize, Invert, Channel Mixer, Gradient Map, Image Size, Canvas Size, Transform Selection, and Rotate Canvas commands, and a limited set of filters. For more information, see "Using filters" in online Help. To take full advantage of Photoshop features, you can convert a 16-bit-per-channel image to an 8-bit-per-channel image. Converting between color modes (Photoshop) 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. Consequently, before converting images, it's best to do the following: • Do as much editing as possible in the image's original mode (usually RGB from most scanners, or CMYK from traditional drum scanners or if imported from a Scitex system). • Save a backup copy before converting. Be sure to save a copy of your image that includes all layers in order to edit the original version of the image after the conversion. • Flatten the file before converting it. The interaction of colors between layer blending modes will change when the mode changes. To convert between 8 bits per channel and 16 bits per channel: 1 To convert to a 16-bit-per-channel image, first flatten the image. (See "Flattening all layers" on page 248.) 2 Choose Image > Mode > 16 Bits/Channel or 8 Bits/Channel. To convert an image to another mode: Choose Image > Mode and the mode you want from the submenu. Modes not available for the active image appear dimmed in the menu. Images are flattened when converted to Multichannel, Bitmap, or Indexed Color mode, because these modes do not support layers. For more information, see "Converting between Grayscale and Bitmap modes (Photoshop)" in online Help.