Re: Screen captures in .GIF format or .JPG format

Subject: Re: Screen captures in .GIF format or .JPG format
From: Max Wyss <prodok -at- prodok -dot- ch>
To: Bill Hartzer <BHartzer -at- cha-systems -dot- com>
Date: Thu, 14 Sep 2000 22:59:46 +0200

Bill,

Your graphics expert friend is absolutely right, but there might be something missing in getting it through. JPEG is a compression algorithm which has been developed for photographic images. It essentially works by dropping information in textured areas (where every pixel has a different color value), by adding some image information which is calculateable (and therefore will take way less space. This algorithm works best in areas with relatively small contrast. However, it creates artefacts around high contrasts.

The GIF format on the other hand uses a lossless compression algorithm which essentially describes the color settings of a row of pixels (so instead of saying 50 times "red", it says "50 times red", which does, of course use less space. This makes it most efficient with big uniformly colored areas. Besides the compression algorithm, it uses only 8 bit for the color encoding (which means that it can access 256 colors, defined in the file by their 24-bit values in a "palette"). As the compression algorithm does not add any information, or change it, there will be no artefacts around, and there are no problems along contrasts.

This in mind, it is pretty obvious that normal screenshots are images with bigger uniformly colored areas and high contrasts. Therefore, the file format to use should be clear.

It may also be useful to do the complete routine for reducing colors and selecting the exact number of colors for the palette. This will reduce the file size of the GIF even more, in order to achieve the smallest possible file size.

A nice overview over all those file formats can be found in the "Alphabet Soup" column of the Wise-Women website (http://www.wise-women.org/resources/abc/graphics).

Hope, this can help.


Max Wyss
PRODOK Engineering
Low Paper workflows, Smart documents, PDF forms
CH-8906 Bonstetten, Switzerland

Fax: +41 1 700 20 37
e-mail: mailto:prodok -at- prodok -dot- ch
http://www.prodok.ch



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Do you save your screen captures in .GIF format or .JPG format?

Our screen captures are used in MS Word for printed documentation and then
converted to html, so we need them to be either a .gif or .jpg file, and
they
all have less than 256 colors. I've been told by a graphics expert friend
that .GIF files are generally used for original artwork (i.e., buttons,
banners, logos, etc.)
and animations, while .JPG files are strictly reserved for photos.

Are screen captures artwork or are they photos?
Which file format is better for screen captures that will end up being
viewed in a web browser?




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