Converting Between Color Modes (Photoshop) - Adobe PHOTOSHOP 6.0 Manual

Converting between bit depths
A 16-bit-per-channel image provides finer distinc-
tions 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.
To convert between 8 bits per channel and 16 bits per
channel:
To convert to a 16-bit-per-channel image, first
1
flatten the image. (See "Flattening all layers" on
page 248.)
Choose Image > Mode > 16 Bits/Channel or
2
8 Bits/Channel.
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 inter-
action of colors between layer blending modes will
change when the mode changes.
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 Multi-
channel, 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.
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User Guide