Color modes, Rgb color mode, Cmyk color mode – Adobe Photoshop CS4 User Manual
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USING PHOTOSHOP CS4
Color fundamentals
Last updated 1/10/2010
Color modes
RGB Color mode
Photoshop RGB Color mode uses the RGB model, assigning an intensity value to each pixel. In 8-bits-per-channel
images, the intensity values range from 0 (black) to 255 (white) for each of the RGB (red, green, blue) components in
a color image. For example, a bright red color has an R value of 246, a G value of 20, and a B value of 50. When the
values of all three components are equal, the result is a shade of neutral gray. When the values of all components are
255, the result is pure white; when the values are 0, pure black.
RGB images use three colors, or channels, to reproduce colors on screen. In 8-bits-per-channel images, the three
channels translate to 24 (8 bits x 3 channels) bits of color information per pixel. With 24-bit images, the three channels
can reproduce up to 16.7 million colors per pixel. With 48-bit (16-bits-per-channel) and 96-bit (32-bits-per-channel)
images, even more colors can be reproduced per pixel. In addition to being the default mode for new Photoshop
images, the RGB model is used by computer monitors to display colors. This means that when working in color modes
other than RGB, such as CMYK, Photoshop converts the CMYK image to RGB for display on screen.
Although RGB is a standard color model, the exact range of colors represented can vary, depending on the application
or display device. The RGB Color mode in Photoshop varies according to the working space setting that you specify
in the Color Settings dialog box.
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CMYK Color mode
In the CMYK mode, each pixel is assigned a percentage value for each of the process inks. The lightest (highlight)
colors are assigned small percentages of process ink colors; the darker (shadow) colors higher percentages. For
example, a bright red might contain 2% cyan, 93% magenta, 90% yellow, and 0% black. In CMYK images, pure white
is generated when all four components have values of 0%.
Use the CMYK mode when preparing an image to be printed using process colors. Converting an RGB image into
CMYK creates a color separation. If you start with an RGB image, it’s best to edit first in RGB and then convert to
CMYK at the end of your editing process. In RGB mode, you can use the Proof Setup commands to simulate the effects
of a CMYK conversion without changing the actual image data. You can also use CMYK mode to work directly with
CMYK images scanned or imported from high-end systems.
Although CMYK is a standard color model, the exact range of colors represented can vary, depending on the press and
printing conditions. The CMYK Color mode in Photoshop varies according to the working space setting that you
specify in the Color Settings dialog box.
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