CYBER NOTES April, 2006 by Dave Benore

TEXT AND GRAPHIC FILES ARE DIFFERENT ANIMALS

All personal computers have two modes of operation, called text and graphics. Normally one does not have to be too concerned about this but if you understand it a little, some things become clearer.

You determine automatically which mode your computer is in by what you do. If you use a word processor to type a letter, your computer works in text mode. If you use a drawing program of any kind, or photography, your computer works in graphics mode.

Text Mode: When you type the letter “a”, your computer registers this as 97, a code that stands for the letter “a”. The letter “A” is coded as 65. Each character, number, letter, or punctuation mark has a numerical code. This is part of the ASCII code (pronounced “asskey”--American Standard Code for Information Interchange). You don’t need to know this code but it helps to know it exists. So when your computer receives data as coded numbers it is working in text mode. Text files store the ADCII codes of alphabetic characters. When the file is sent to your monitor the word processing program uses the stored codes to tell the monitor which pixels to energize—to “light up”. (Your monitor screen, like a TV set, is made up of rows and columns of picture elements called “pixels”. Each pixel has an “address” made up of the row number and the column number of the pixel.)

Graphics Mode: Graphics mode works very differently. Graphics files store information about each pixel, without knowing what the pixel represents. A graphics program reads the graphics file and determines which pixels to energize, pixel by pixel. This is called “bit-mapping”, or sometimes “imaging”. Images, photos, graphs, etc. are shown to you on your monitor by energizing the correct pixels. This is why files containing photos are so big. Each pixel needs information about its color, brightness, color intensity, etc. A photo will have one or maybe ten million pixels that need all of this kind of information for each pixel.

Many people that use digital cameras are familiar with JPEG files. JPEG files have a filename extension of .jpg. JPEG is a system of compressing bit-mapped files into something very much smaller without loosing much information. This makes the file size much smaller.

More and more files are being sent over the Internet via “Adobe Acrobat”, or .pdf files. These are files which are images of the original text file. Because they are only images, you cannot edit or change them. Text and Graphics files are different animals. Happy Computing!

P.S. Please see the Events and Activities Section of this paper for the computer class schedule starting April 17, 2006