BBS: Inland Empire Archive Date: 11-16-92 (08:21) Number: 303 From: HARRY GISH Refer#: NONE To: BOB OEHRLE Recvd: NO Subj: PCX files How to read ?? Conf: (2) Quik_Bas
BO> Would like to find out how Pcx files are organized BO> so that I can then BO> use BLOAD to plot on the screen. The files that I BO> am interested in viewing BO> are 43830 bytes long. I have copied these files Why use BLOAD? Just do a PCX reader. It's easier in this case since you are limiting yourself to a specific situation (when you're doing a general PCX reader you have to allow for 3 distinct formats, 2, 16 and 256 color files). All you really need to do is double-check the absolute size , which is located in bytes 8-11 from the beginning of the file in the 128 byte header. The 16 color definitions (which you restore and set using PALETTE) are in the 48 bytes starting at byte 17, and are the red, green, and blue intensities respectively. The actual encoding starts at byte 128 and works this way : If the byte is greater than 191 it is a multiplier otherwise it is data {be VERY careful in logicing this out. The multiplier can be between 1 and 63 only AND the only way to encode a data value greater than 191 is with a multiplier first. Thus a one code of data 243 would have to be encoded as a 1 multiplier of 243. This is what makes a 320X200X256 color PCX, which should be 64000 maximum ... plus resolution and palette header info ... often baloon up to 70-80K). Anyway, the data is encoded into groups of 8 pixel values and in 4 "scans". Thus you actually read an X line 4 times, accumulating the binary values to range from 0 to 15 for each pixel. --- Maximus/2 2.01wb * Origin: ACCESS BBS (1:124/2122)
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