User Guide

CHAPTER 3
42
Getting Images into Photoshop
Because computer monitors represent images by
displaying them on a grid, both vector and bitmap
images are displayed as pixels on-screen.
About image size and resolution
To produce high-quality images using Photoshop,
it is important to understand how the pixel data of
bitmap images is measured and displayed. For
more on how pixel data is displayed as color, see
“About bit depth” on page 68.
Pixel dimensions The number of pixels along the
height and width of a bitmap image. The display
size of an image on-screen is determined by the
pixel dimensions of the image plus the size and
setting of the monitor. The file size of an image is
proportional to its pixel dimensions.
A typical 13-inch monitor displays 640 pixels
horizontally and 480 vertically. An image with
pixel dimensions of 640 by 480 would fill this small
screen. On a larger monitor with a 640 by 480
setting, the same image (with pixel dimensions of
640 by 480) would still fill the screen, but each
pixel would appear larger. Changing the setting of
this larger monitor to 1152 pixels by 870 pixels
would display the image at a smaller size,
occupying only part of the screen.
When preparing an image for online display (for
example, a Web page that will be viewed on a
variety of monitors), pixel dimensions become
especially important. Because your image may be
viewed on a 13-inch monitor, you’ll probably want
to limit the size of your image to a maximum of
640 pixels by 480 pixels.
BITMAP VS. VECTOR A bitmap image is composed
of a grid of small squares known as pixels. A vector
graphic is defined by mathematical objects called
vectors.
Bitmap images are good at reproducing subtle grada-
tions of color, as in photographs. They can show jagged
edges when printed at too large a size or displayed at too
high a magnification.
Vector graphics are good at reproducing crisp outlines,
as in logos or illustrations. They can be printed or dis-
played at any resolution without losing detail.
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