Converting ZSoft Files to PC Paint Files
                        by Bob Montgomery
                        Orlando, Florida

If  you  have an EGA display, PC Paint is a  wonderful  tool  for 
doing color graphics. It comes with the Mouse Systems mouse,  and 
can  be purchased seperately. A mouse is almost a must for  doing 
graphics  work, and is relatively cheap. Another  color  graphics 
program  along the same lines is PC Paintbrush (by Zsoft),  which 
comes  with  the  Microsoft  mouse. The  two  programs  are  very 
similar, but each one does certain things better than the  other. 

ZSoft Files
ZSoft  picture  files have a 128 byte header with  the  following 
significance:
     Byte Manufacturer = 10
     Byte Version = 5
     Byte Encode = 1
     Byte Bits/pixel = 1
     Word X1 = Start X offset = 0
     Word Y1 = Start Y offset (from top) = 0
     Word X2 = End X offset = 0
     Word Y2 = End Y offset = 0
     Palette = 48 bytes (explained below)
     Byte Video mode = 0
     Byte Planes = 4
     Word Bytes/line = 80
     60 filler bytes = 0

The palette data has 3 bytes for each palette register; there are 
16   3  byte  groups  of palette data. The 3  bytes  in  a  group 
correspond to red, green, blue from left to right. Each byte  can 
have  the  hex value 0, 55h, AAh, or FFh,  which  corresponds  to 
color levels none, secondary, normal, and both respectively.  The 
palette register values (0-63) are derived from the bits:
     0  0  sec_red  sec_green  sec_blue  red  green  blue
Thus,  a  group 00 55 FF specifies no red, secondary  green,  and 
normal and secondary blue. This translates to a palette  register 
value of 0+16+9=25.

The packed data uses the following rules:
     1.  If 2 msb's are both 1's, then this is a run count  byte. 
         The  run count is the 6 lsb's, and the data to write  is
         the  next byte. 
     2.  If the 2 msb's are not both 11, write this byte.
Note that for a single screen data byte with both msb's set,  the 
packed  data  contains 2 bytes; a count byte C1h and  the  screen 
data  byte. In general, ZSoft picture files are about 30%  larger 
than PC Paint picture files.

The  data is packed a line at a time starting at the  upper  left 
corner  of the display. All the line data for the blue plane  (0) 
is packed first, then the green plane (1) line data, then the red 
plane (2) line data, then the intensity plane (3) line data. When 
all  plane data for the 1st line has been packed, the plane  data 
for the 2nd line is packed, etc. This is continued until the  end 
of  the  last screen line. When unpacking, keep going  until  the 
file data is exhausted.

PC Paint Files
PC  Paint  files  are  saved in at  least  6  different  formats,  depending
on  the version and who created them. The file format for the full page  packed
version consists of a file header and blocks of packed data.

The file header consists of the following info:
     Word      Identifier 1234 hex
     Word      Horizontal size (pixels)
     Word      Vertical size (pixels)
     Word      X offset into picture (not used)
     Word      Y offset into picture (not used)
     Byte      Bits/pixel (4 for EGA and 2 for CGA)
     Byte      ID - Should be FF hex for PC Paint 2.00 picture
     Byte      Video mode - should be ASCII G for EGA picture
     Byte      Descriptor - should be 3 for EGA pics
     Byte      Bytes of info to follow - should be 16 for EGA pic
  16 Bytes     Palette for picture (2 bytes for CGA pictures)
     
The  packed  blocks follow the header. Each block has  a  5  byte 
block header which gives:
     Word      Packed block size (including header)
     Word      Unpacked block size
     Byte      Run Marker to identify packed data

Each  block  consists  of  screen  data  bytes  and  packed  data 
subblocks. A packed data subblock is identified by the run marker 
for that block, and consists of the following info:
     Byte      Run Marker
     Byte      Run length (bytes)
     Byte      Screen data for run
If  the run length byte is zero, then the run length is the  next 
word, and the screen data byte for the run is the next byte. Each 
screen  data  byte  corresponds to 2 pixels for a  16  color  EGA 
pictures,  and  4 pixels for a 4 color CGA pictures.  Pixels  are 
written  from  left to right on each horizontal line.  Lines  are 
written  from the last line up; the last line is  written  first, 
then the next to last line, etc.

For  a  16  color  EGA picture, there  are  4  bits/pixel  and  2 
pixels/byte.  The  most significant nibble is the color  for  the 
left pixel, and the least significant nibble is the color for the 
right pixel.