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Some commonly used formats:

Compression possible
tagged image file
graphic image file
.jpg / .jpeg


The file size of the same image -- same size, seemingly same quality -- can go down from a 650 KB bitmap to a 16 KB compressed jpg.
Obviously, the latter loads faster. See various image formats and same image with different rates of compression.
The compression rate varies according to the quality of the original image. A high quality image, such as that of the zebra, may be compressed 70% for computer display without appreciable loss of quality.
Therefore, for a computer or web page, you should use compressed images in .gif or .jpg format.

File size, image size, resolution:
To see the FILE SIZE, find your image file with Windows Explorer, with View Details selected.
To see the IMAGE SIZE, open the image, right-click, click Properties. It will give you the size in either pixels or inches. Yes, Virginia, you can FORCE  the image into a smaller space by changing the box containing it in your document or web file -- this will keep you from having to scroll but will not decrease the file size.
To do this properly, you should RESIZE the image to the desired height and width.  You can do this for a single or a number of images in one go with Photoshop, PaintShopPro, or, most easily, with Digital Photo Slideshow software -- see below.
RESOLUTION is the other factor that affects file size. Digital photos or scanned images may have a very high resolution suitable for high quality printing.
For a computer or web page, you should have a resolution of between 72 and 96 dpi, in .gif or .jpg compressed format. Again, the three software packages named above will let you do this, for individual or batched images.

Image sources: see | Scanning | Photography | more on photography | Photography Tips |
Download images from the Web or copy them from a CD but make sure to do so legally and with permission and credits.

Image creating and editing software:
Paint (basic and free; it comes with MS Windows)
Picasa Photo Management (free from Google, for the time being -- download and install): http://www.picasa.com/
affordable and very good: Jasc PaintShopPro, Adobe Photoshop Elements, Ulead PhotoImpact
expensive and excellent professional package but hard to learn: Adobe Photoshop

Digital Photo Slideshow -- you can resize, change format, create a slide show, and much more: free download, $20 to buy.

Check out Impatica to easily compress a PowerPoint presentation for the web -- my 70 MB file changed to a 2 MB file.

Basics of image editing:  edit an image, in PaintShopPro or in PhotoShop

Some good web pages on graphics

GRIN (Great Images in NASA Library of Images)

Ursula Hoffmann -- last rev. Jan. 2006