About Image Size And Resolution - Adobe PHOTOSHOP 6.0 Manual

CHAPTER 2
92
Getting Images into Photoshop and ImageReady
Vector graphics are resolution-independent—
that is, they can be scaled to any size and printed
at any resolution without losing detail or clarity.
As a result, vector graphics are the best choice for
representing bold graphics that must retain crisp
lines when scaled to various sizes—for example,
logos.
Vector graphics are good for reproducing crisp outlines, as in
logos or illustrations. They can be printed or displayed at any
resolution without losing detail.
Because computer monitors represent images by
displaying them on a grid, both vector and bitmap
data is displayed as pixels on-screen.

About image size and resolution

In order to produce high-quality images, it is
important to understand how the pixel data of
images is measured and displayed.
Pixel dimensions
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 number of pixels along
For example, a 15-inch monitor typically
displays 800 pixels horizontally and 600 vertically.
An image with dimensions of 800 pixels by
600 pixels would fill this small screen. On a larger
monitor with an 800-by-600-pixel setting, the
same image (with 800-by-600-pixel dimensions)
would still fill the screen, but each pixel would
appear larger. Changing the setting of this larger
monitor to 1024-by-768 pixels would display
the image at a smaller size, occupying only part of
the screen.
3:1
When preparing an image for online display
(for example, a Web page that will be viewed on a
variety of monitors), pixel dimensions become
24:1
especially important. Because your image may be
viewed on a 15-inch monitor, you may want to
limit the size of your image to 800-by-600 pixels to
allow room for the Web browser window controls.
15"
832 x 624 / 640 x 480
How large an image appears on-screen depends on a combina-
tion of factors––the pixel dimensions of the image, the monitor
size, and the monitor resolution setting. The examples above
show a 620-by-400-pixel image displayed on monitors of
various sizes and resolutions.
20"
1024 x 768 / 640 x 480