Adobe Photoshop CS4 - Manual (Page 65)

58 USING PHOTOSHOP CS4
Opening and importing images
Last updated 1/10/2010
Quickly display the current image size
If you want to quickly display a document’s current image size, use the information box at the bottom of the document
window.
❖ Position the pointer over the file information box, and hold down the mouse button.
More Help topics
“ Display file information in the document window ” on page 35
File size
The file size of an image is the digital size of the image file, measured in kilobytes (K), megabytes (MB), or gigabytes
(GB). File size is proportional to the pixel dimensions of the image. Images with more pixels may produce more detail
at a given printed size, but they require more disk space to store and may be slower to edit and print. Image resolution
thus becomes a compromise between image quality (capturing all the data you need) and file size.
Another factor that affects file size is file format. Because of the varying compression methods used by GIF, JPEG, and
PNG file formats, file sizes can vary considerably for the same pixel dimensions. Similarly, color bit-depth and the
number of layers and channels in an image affect file size.
Photoshop supports a maximum pixel dimension of 300,000 by 300,000 pixels per image. This restriction places limits
on the print size and resolution available to an image.
About monitor resolution
Your monitor’s resolution is described in pixel dimensions. For example, if your monitor resolution and your photo’s
pixel dimensions are the same size, the photo will fill the screen when viewed at 100%. How large an image appears
on-screen depends on a combination of factors—the pixel dimensions of the image, the monitor size, and the monitor
resolution setting. In Photoshop, you can change the image magnification on-screen, so you can easily work with
images of any pixel dimensions.
A 620- by 400-pixel image displayed on monitors of various sizes and resolutions.
When preparing images for viewing on-screen, you should consider the lowest monitor resolution that your photo is
likely to be viewed on.
About printer resolution
Printer resolution is measured in ink dots per inch, also known as dpi. Generally, the more dots per inch, the finer the
printed output you’ll get. Most inkjet printers have a resolution of approximately 720 to 2880 dpi. (Technically, inkjet
printers produce a microscopic spray of ink, not actual dots like imagesetters or laser printers.)
Printer resolution is different from, but related to image resolution. To print a high quality photo on an inkjet printer,
an image resolution of at least 220 ppi should provide good results.
15"
20"
1024 x 768 / 640 x 480 832 x 624 / 640 x 480