Enlarging Bitmaps
Unfortunately, bitmap images do not lend themselves to being enlarged. Though photographs can be enlarged somewhat and still look convincing, any image scaled to a noticeably larger size will suffer in quality. For this reason it is sometimes wise to keep a set of original images on file. The originals should be saved before any sizing or other manipulation is done to the image.

100x75	250x188
This 100x75 pixel image was resized to 250x188 with less than desirable results.

Sizing Down
An image can usually be sized smaller and still retain its quality. You should confirm that your image editor supports anti-aliasing (almost all editors do). With anti-aliasing a reduced image will still look like the original even though it will have fewer pixels. (Anti-alisaing is a method for reducing the jagged look of a bitmap image.)

This 200x250 pixel image was reduced to 150x188 then to 75x94 with little loss of quality.

Clearing Up the Fuzzies
However, if an image is reduced enough the anti-aliasing feature will eventually give you a somewhat blurred image. Many graphics programs come with filters that can help you enhance a photograph's blurred appearance. The Figure 4 photograph was reduced from a very large original, resulting in a slightly blurred image. Figure 5 is the same photograph after a "Sharpen" filter has been applied.

Figure 4

Figure 5

What size image should I use?
Web images can be of any pixel dimension depending on the desired effect and use of the image. Images of varying size can be used to balance and give an overall pleasing appearance to any web page. What is often more important than the image dimension is the actual file size of an image. A web page with beautiful images that takes too long to load may cause your audience to become frustrated and move on.

This netStartClass web page uses several images of varying size. The top image (1) spans almost the entire width of the web page. Its dimension are 664x104 with a file size of 18k. Images 2, 3, and 4 are all 110 pixels wide and with a file size of 6k, 1k, and 1k respectively. The entire page, including text, is less than 40k and takes less than 5 seconds to download with a 56k modem connection.

The next section of this article deals with file optimization and can aid you in obtaining the best image for the smallest file size.