Color Channels - Adobe 13102498 - Photoshop CS3 - Mac User Manual

PHOTOSHOP CS3 59
User Guide
3:1
24:1
Example of a vector image at different levels of magnification
You can freely move or modify vector graphics without losing detail or clarity, because they are resolution-
independent—they maintain crisp edges when resized, printed to a PostScript printer, saved in a PDF file, or
imported into a vector-based graphics application. As a result, vector graphics are the best choice for artwork, such
as logos, that will be used at various sizes and in various output media.
The vector objects you create using the drawing and shape tools in Adobe Creative Suite are examples of vector
graphics. You can use the Copy and Paste commands to duplicate vector graphics between Creative Suite compo-
nents.
See also
"About bitmap images" on page 58
Combining vector graphics and bitmap images
When combining vector graphics and bitmap images in a document, it's important to remember that how your
artwork looks on-screen isn't always how it will look in its final medium (whether commercially printed, printed on
a desktop printer, or viewed on the web). The following factors influence the quality of your final artwork:
Many effects add partially transparent pixels to your artwork. When your artwork contains trans-
Transparency
parency, Photoshop performs a process called flattening before printing or exporting. In most cases, the default
flattening process produces excellent results. However, if your artwork contains complex, overlapping areas and you
require high-resolution output, you will probably want to preview the effects of flattening.
The number of pixels per inch (ppi) in a bitmap image. Using too low a resolution for a printed
Image Resolution
image results in pixelation—output with large, coarse-looking pixels. Using too high a resolution (pixels smaller than
what the output device can produce) increases the file size without increasing the quality of the printed output, and
slows the printing of the artwork.
The number of ink dots produced per inch (dpi) and the number of lines
Printer resolution and screen frequency
per inch (lpi) in a halftone screen. The relationship between image resolution, printer resolution, and screen
frequency determines the quality of detail in the printed image.

Color channels

Every Photoshop image has one or more channels, each storing information about color elements in the image. The
number of default color channels in an image depends on its color mode. By default, images in Bitmap, Grayscale,
Duotone, and Indexed Color mode have one channel; RGB and Lab images have three; and CMYK images have four.
You can add channels to all image types except Bitmap mode images. For more information, see "Color modes" on
page 110.
Channels in color images are actually grayscale images that represent each of the color components of an image. For
example, an RGB image has separate channels for red, green, and blues color values.