Adobe 13101332 - Photoshop - Mac User Manual page 63

Adobe Photoshop Help
Using Help | Contents
Image resolution The number of pixels displayed per unit of printed length in an image,
usually measured in pixels per inch (ppi). In Photoshop, you can change the resolution of
an image; in ImageReady, the resolution of an image is always 72 ppi. This is because the
ImageReady application is tailored to creating images for online media, not print media.
In Photoshop, image resolution and pixel dimensions are interdependent. The amount of
detail in an image depends on its pixel dimensions, while the image resolution controls
how much space the pixels are printed over. For example, you can modify an image's
resolution without changing the actual pixel data in the image—all you change is the
printed size of the image. However, if you want to maintain the same output dimensions,
changing the image's resolution requires a change in the total number of pixels.
Example of an image at 72-ppi and 300-ppi
When printed, an image with a high resolution contains more, and therefore smaller,
pixels than an image with a low resolution. For example, a 1-by-1-inch image with a
resolution of 72 ppi contains a total of 5184 pixels (72 pixels wide x 72 pixels high = 5184).
The same 1-by-1-inch image with a resolution of 300 ppi contains a total of 90,000 pixels.
Higher-resolution images usually reproduce more detail and subtler color transitions than
lower-resolution images. However, increasing the resolution of a low-resolution image
only spreads the original pixel information across a greater number of pixels; it rarely
improves image quality.
Using too low a resolution for a printed image results in pixelation—output with large,
coarse-looking pixels. Using too high a resolution (pixels smaller than the output device
can produce) increases the file size and slows the printing of the image; furthermore, the
device will be unable to reproduce the extra detail provided by the higher resolution
image.
Monitor resolution The number of pixels or dots displayed per unit of length on the
monitor, usually measured in dots per inch (dpi). Monitor resolution depends on the size
of the monitor plus its pixel setting. Most new monitors have a resolution of about 96 dpi,
while older Mac OS monitors have a resolution of 72 dpi.
Using Help | Contents
Getting Images into Photoshop and ImageReady
| Index
| Index
Back 63
Back 63