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Image Formats
- The two most common graphic file formats on the web are GIF
(Graphic Interchange Format), JPEG (Joint Photographic
Experts Group) with the newcomer to the web graphic world being PNG (Portable Network
Graphics).
- Why are they used?
- These file formats are used on the web because they have the best
compression. Compression is the technique used to take a large file
and turn it into a smaller file by applying a fancy mathematical
algorithm to it. Since many users are accessing web pages on 28.8
modems, the smaller the file, the more quickly it can be transferred
over the net.
- Image size is no joke. If your images take too long to load, a user
will never even bother to wait to read about what you have to say.
- A good rule of thumb is that you should use GIF files for images
and JPEG files for photographs. [1]
- The GIF format is also interesting because of the amount of
"special effects" it provides. Besides a standard GIF file, you can
easily download freeware programs to create interlaced GIF files,
transparent GIF files, and animated GIF files. Let's look at each...
- An interlaced GIF file is a file that loads in pieces. It starts
out fuzzy and continually focuses until it is in perfect focus.
Interlacing does not actually speed up the loading of the image, but it
does make a user feel as if it does because they can watch it
materialize. Below is an example of an interlaced GIF.
- Transparent GIF's allow you to specify a single color that will
become transparent, thus allowing the background to show through. This
is useful when you want to create the illusion of irregularly shaped
artwork such as when you add text art to your page. Instead of getting
an ugly square box around your text, a transparent GIF will make the
type appear to blend right into the page. The following example shows
the same image, one with no transparency and one with a transparent
background.
- Animated GIF files allow you to merge several images into one in
order to create a cell animation. Note that for each cell, the image
is that much larger, so you must take care to make your animation in as
few cells as possible.
- Here is an example of an animated GIF
- PNG
is a lossless, portable, well-compressed RGB file format
that can include mask-channel information as well as
progressive display for on-line use.
Image Format Resources
Creating Images
Introduction to Web Design | Table of Contents
Image Size
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