|
Graphics_for_the_web_GIF_Format
| Graphics for the web: GIF Format
The GIF (Graphics Interchange Format) format was invented in
1987 by Compuserve to allow images to be displayed. This format
allows for 256 colors (which was a lot at the time),
compression, interlacing and animation. It is a very powerful
format, suitable for many different types of images.
Due to the limited number of colors, GIF is primarily useful in
images with a distinct separation of colors. A cartoon, for
example, is ideal for the GIF format.
When you save an image in GIF format, you have the option to
specify how many colors will be saved. By doing this you can
decrease the size of an image even further. All of the tools
which are available to optimize GIF images work by reducing the
number of colors to the bare minimum. This can produce
astounding results in the size of the finished file.
Unlike JPEG, GIF uses a non-lossy compression algorithm. This
means that images do not loose bits when they are decompressed.
In order to accomplish this, GIF uses a proprietary
encoding/decoding scheme called LZW (Lempel Zev Welch). LZW is
an excellent compression algorithm which typically results in
very small files (in comparison to fully expanded BMP files).
This compression method is actually the cause of a bit of
controversy. As it turns out, LZW is owned by UniSys, and over
the past few years they have made some attempts to collect
licensing fees for products which save in the GIF format. These
attempts have had mixed results, and has caused the development
of a new non-proprietary standard called PNG.
You may indicate that a color in a GIF image is transparent,
meaning whatever is below the image will show through.
The GIF89a standard included animation, which basically allows
multiple images to be included in a single GIF file. In that
image you can specify the timing that the frames are shown and
whether or not the animation stops or loops forever.
Interlacing is a cool feature which allows graphics to be "faded
in". Initially a very low quality image is displayed, and bits
are slowly added as the entire image is received. GIF supports
this feature, which is useful for displaying very large images
quickly.
An interesting albeit little known fact about GIF images is that
they can include comments, which take up space and make the
graphic larger. There are a number of products which will remove
these comments. I found that the freeware program called
GIFclean is simple to use and works well.
About the author:
Richard Lowe Jr. is the webmaster of Internet Tips And Secrets.
This website includes over 1,000 free articles to improve your
internet profits, enjoyment and knowledge. Web Site Address:
http://www.internet-tips.net Weekly newsletter:
http://www.internet-tips.net/joinlist.htm Daily Tips:
mailto:internet-tips@GetResponse.com
|
|
| |
| |
