Timex Tips

QUESTION: Can you explain the term RLE graphics?

ANSWER: R.L.E. stands for RUN LENGTH ENCODED graphics, which probably does not tell you a lot. The idea is to take а screen full of graphic information (usually 256 dots across by 196 dots high) and turn the information into ASCII characters which сап then be sent via modem to other computers. At the other end, the ASCII characters are turned back into a visible screen which can bе SAVEd. This is not just a system for use with Timex-Sinclair computers, but is in wide use with various makes. There are several public domain programs that encode and decode the screen information to and from RLE format. Most of the BASIC programs will ignore the bottom two print lines since the PLOT command will not work there. Machine code decoders can use the bottom lines. If you would like to write your own program, here are the basics: First, the encoding starts with capital GH to mark the beginning of the file. Then, the encoding program starts at the upper left corner of the screen and counts the number of black dots that appear in a row, counting to the right. Let’s sау there are three black dots and then а white dot followed by two more black dots. Since we are going to use ASCII characters for our encoding (space thru copyright or CHR$ 32 thru 127), wе are going to assign space with the value zero, exclamation with the value one, quotes with the value two, and so on down to copyright with the value of 95. Therefore, our first encoded character will be # because it has a value of three followed by ! because it is one and finally a ‘ because it represents two. This counting of black dots and white dots continues across the screen. When the right edge of the screen is reached, drop to the next line at the far left and keep counting. That is, five black dots at the end of a line followed by three black dots at the beginning of the next line would be encoded as an eight. If we need a value of more than 95, (like if the whole top line is black dots), then we encode 95 for black, zero for white, and 95 more for black and so on. The last character in the file is not ASCII but is a CHR$ 7 (bell). A complicated picture may easily take much more memory space than a SCREEN$ but keep іп mind that this system іs compatible with other makes of computers and is easily transmitted via modem systems which only accept ASCII characters. Examples of encoded pictures are available from many BBSs and are usually named with the suffix RLE (A picture of Brooke Shields might be named BROOKE.RLE). On CompuServe you can GO PICS at any ! prompt. This method of receiving and decoding graphics adds a whole new dimension to computing.