ZSoft PCX File Format

This booklet was designed to aid developers and users in understanding
the technical aspects of the .PCX file format and the use of FRIEZE.
Any comments, questions or suggestions about this booklet should be sent

ZSoft Corporation
Technical Services
ATTN: Code Librarian
450 Franklin Rd. Suite 100
Marietta, GA  30067

Technical Reference Manual information compiled by:
Dave Steier & Dean Ansley

Revision 5

To down load additional information and the source for a complete Turbo
Pascal program to show .PCX files on a CGA/EGA/VGA graphics display,
call our BBS at (404)427-1045.  You may use a 9600 baud  modem or a 2400
baud standard modem.  Your modem should be set for 8 data bits, 1 stop
bit, and NO parity.

Image  File (.PCX) Format

If you have technical questions on the format, please do not call
technical support.  ZSoft provides this document as a courtesy to its
users and developers.  It is not the function of Technical Support to
provide programming assistance.  If something is not clear, leave a
message on our BBS, Compuserve, or write us a letter at the above
address.  The information in this section will be useful if you want to
write a program to read or write PCX files (images).  If you want to
write a special case program for one particular image format you should
be able to produce something that runs twice as fast as "Load from..."
in PC Paintbrush.  

Image files used by PC Paintbrush product family and FRIEZE (those with
a .PCX extension) begin with a 128 byte header.  Usually you can ignore
this header, since your images will probably all have the same
resolution.  If you want to process different resolutions or colors, you
will need to interpret the header correctly.  The remainder of the image
file consists of encoded graphic data.  The encoding method is a simple
byte oriented run-length technique.  We reserve the right to change this
method to improve space efficiency.  When more than one color plane is
stored in the file, each line of the image is stored by color plane
(generally ordered red, green, blue, intensity), As shown below.  Scan
line 0:
        RRR...	(Plane 0)
	GGG...	(Plane 1)
	BBB...	(Plane 2)
	III...		(Plane 3)
Scan line 1:
	III...		(etc.)

The encoding method is:
    FOR  each  byte,  X,  read from the file
        IF the top two bits of X are  1's then
            count = 6 lowest bits of X
            data = next byte following X
            count = 1
            data = X
Since the overhead this technique requires is, on average,  25% of the
non-repeating data and is at least offset whenever bytes are repeated,
the file storage savings are usually considerable.

Byte	Item	Size	Description/Comments
0	Manufacturer	1	Constant Flag, 10 = ZSoft .pcx
1	Version	1	Version information
			0 = Version 2.5 of PC Paintbrush
			2 = Version 2.8 w/palette information
			3 = Version 2.8 w/o palette information
			4 = PC Paintbrush for Windows(Plus for Windows uses Ver 5)
			5 = Version 3.0 and > of PC Paintbrush and PC
                            Paintbrush +, includes Publisher's Paintbrush.
                            Includes 24-bit .PCX files
2	Encoding	1	1 = .PCX run length encoding
3	BitsPerPixel	1 Number of bits to represent a pixel (per Plane)
                            - 1, 2, 4, or 8
4	Window	8	Image Dimensions: Xmin,Ymin,Xmax,Ymax
12	HDpi	2	Horizontal Resolution of image in DPI*
14	VDpi	2	Vertical Resolution of image in DPI*
16	Colormap	48 	Color palette setting, see text
64	Reserved	1	Should be set to 0.
65	NPlanes	1	Number of color planes
66	BytesPerLine	2	Number of bytes to allocate for a scanline
                                plane.  MUST be an EVEN number.  Do NOT
                                calculate from Xmax-Xmin.
68	PaletteInfo	2	How to interpret palette-
                                1 = Color/BW,
                                2 = Grayscale (ignored in PB IV/ IV +)
70	HscreenSize	2	Horizontal screen size in pixels.
New field found only in PB IV/IV Plus
72	VscreenSize	2	Vertical screen size in pixels.
New field found only in PB IV/IV Plus
74	Filler	54	Blank to fill out 128 byte header.
                        Set all bytes to 0

All sizes are measured in BYTES. 
All variables of SIZE 2 are integers.  
*HDpi and VDpi represent the Horizontal and Vertical resolutions which
the image was created (either printer or scanner); i.e. an image which
was scanned might have 300 and 300 in each of these fields.

Decoding .PCX Files
First, find the pixel dimensions of the image by calculating [XSIZE =
Xmax - Xmin + 1] and [YSIZE = Ymax - Ymin + 1].  Then calculate how many
bytes are required to hold one complete uncompressed scan line:

TotalBytes = NPlanes * BytesPerLine

Note that since there are always an even number of bytes per scan line,
there will probably be unused data at the end of each scan line.
TotalBytes shows how much storage must be available to decode each scan
line, including any blank area on the right side of the image.  You can
now begin decoding the first scan line - read the first byte of data
from the file.  If the top two bits are set, the remaining six bits in
the byte show how many times to duplicate the next byte in the file.  If
the top two bits are not set, the first byte is the data itself, with a
count of one.

Continue decoding the rest of the line.  Keep a running subtotal of how
many bytes are moved and duplicated into the output buffer.  When the
subtotal equals TotalBytes, the scan line is complete.  There should
always be a decoding break at the end of each scan line.  But there will
not be a decoding break at the end of each plane within each scan line.
When the scan line is completed, there may be extra blank data at the
end of each plane within the scan line.  Use the XSIZE and YSIZE values
to find where the valid image data is.  If the data is multi-plane,
BytesPerLine shows where each plane ends within the scan line.

Continue decoding the remainder of the scan lines (do not just read to
end-of-file).  There may be additional data after the end of the image
(palette, etc.)

Palette Information Description

EGA/VGA 16 Color Palette Information

The palette information is stored in one of two different formats.  In
standard RGB format (IBM EGA, IBM VGA) the data is stored as 16 triples.
Each triple is a 3 byte quantity of Red, Green, Blue values.  The values
can range from 0-255, so some interpretation may be necessary.  On an
IBM EGA, for example, there are 4 possible levels of RGB for each color.
Since 256/4 = 64, the following is a list of the settings and levels:

Setting		Level
0-63		0
64-127		1
128-192		2
193-254		3
24-Bit .PCX Files
24 bit images are stored as version 5 or above as 8 bit, 3 plane images.
24 bit images do not contain a palette.
Bit planes are ordered as lines of red, green, blue in that order.

VGA 256 Color Palette Information

ZSoft has recently added the capability to store palettes containing
more than 16 colors in the .PCX image file.  The 256 color palette is
formatted and treated the same as the 16 color palette, except that it
is substantially longer.  The palette (number of colors x 3 bytes in
length) is appended to the end of the .PCX file, and is preceded by a 12
decimal.  Since the VGA device expects a palette value to be 0-63
instead of 0-255, you need to divide the values read in the palette by

To access a 256 color palette:

First, check the version number in the header; if it contains a 5 there
is a palette.

Second, read to the end of the file and count back 769 bytes.  The value
you find should be a 12 decimal, showing the presence of a 256 color

CGA Color Palette Information

NOTE: This is no longer supported for PC Paintbrush IV/IV Plus.

For a standard IBM CGA board, the palette settings are a bit more
complex.  Only the first byte of the triple is used.  The first triple
has a valid first byte which represents the background color.  To find
the background, take the (unsigned) byte value and divide by 16.  This
will give a result between 0-15, hence the background color.  The second
triple has a valid first byte, which represents the foreground palette.
PC Paintbrush supports 8 possible CGA palettes, so when the foreground
setting is encoded between 0 and 255, there are 8 ranges of numbers and
the divisor is 32.

CGA Color Map

Header Byte #16 

Background color is determined in the upper four bits.

Header Byte #19

Only upper 3 bits are used, lower 5 bits are ignored.  The first three
bits that are used are ordered C, P, I.  These bits are interpreted as

c: color burst enable - 0 = color; 1 = monochrome
p: palette - 0 = yellow; 1 = white
i: intensity - 0 = dim; 1 = bright
PC Paintbrush Bitmap Character Format

NOTE: This format is for PC Paintbrush (up to Vers 3.7) and PC
Paintbrush Plus (up to Vers 1.65)

The bitmap character fonts are stored in a particularly simple format.
The format of these characters is as follows:

font width	byte		0xA0 + character width  (in pixels)
font height	byte		character height  (in pixels)
Character Width Table
char widths	(256 bytes) 	each char's width + 1 pixel of kerning
Character Images
(remainder of the file)		starts at char 0  (Null)

The characters are stored in ASCII order and as many as 256 may be
provided.  Each character is left justified in the character block, all
characters take up the same number of bytes.

Bytes are organized as N strings, where each string is one scan line of
the character.

For example, each character in a 5x7 font requires 7 bytes.  A 9x14 font
uses 28 bytes per character (stored two bytes per scan line in 14 sets
of 2 byte packets).  Custom fonts may be any size up to the current
maximum of 10K bytes allowed for a font file.  There is a maximum of 4
bytes per scan line.Sample "C" Routines

The following is a simple set of C subroutines to read data from a .PCX

/* This procedure reads one encoded block from the image file and stores
   a count and data byte.
Return result:  0 = valid data stored, EOF = out of data in file */
encget(pbyt, pcnt, fid)
int *pbyt;	/* where to place data */
int *pcnt;	/* where to place count */
FILE *fid;	/* image file handle */
int i;
	*pcnt = 1;	/* assume a "run" length of one */
	if (EOF == (i = getc(fid)))
		return (EOF);
	if (0xC0 == (0xC0 & i))
		*pcnt = 0x3F & i;
		if (EOF == (i = getc(fid)))
			return (EOF);
	*pbyt = i;
	return (0);

/* Here's a program fragment using encget.  This reads an entire file
   and stores it in a (large) buffer, pointed to by the variable "bufr".
   "fp" is the file pointer for the image */
int i;
long l, lsize;
	lsize = (long )hdr.BytesPerLine * hdr.Nplanes * (1 + hdr.Ymax - hdr.Ymin);
	for (l = 0; l < lsize; )             /* increment by cnt below */
		if (EOF == encget(&chr, &cnt, fp))
		for (i = 0; i < cnt; i++)
			*bufr++ = chr;
		l += cnt;

The following is a set of C subroutines to write data to a .PCX file.

/* Subroutine for writing an encoded byte pair (or single byte if it
   doesn't encode) to a file.  It returns the count of bytes written, 0 if
   error */
encput(byt, cnt, fid)
unsigned char byt, cnt;
FILE *fid;
  if (cnt) {
	if ((cnt == 1) && (0xC0 != (0xC0 & byt)))
		if (EOF == putc((int )byt, fid))
			return(0);     /* disk write error (probably full) */
		if (EOF == putc((int )0xC0 | cnt, fid))
			return (0);      /* disk write error */
		if (EOF == putc((int )byt, fid))
			return (0);      /* disk write error */
		return (2);
   return (0);

/* This subroutine encodes one scanline and writes it to a file.
It returns number of bytes written into outBuff, 0 if failed. */
encLine(inBuff, inLen, fp)
unsigned char *inBuff;    /* pointer to scanline data */
int inLen;			/* length of raw scanline in bytes */
FILE *fp;			/* file to be written to */
unsigned char this, last;
int srcIndex, i;
register int total;
register unsigned char runCount;     /* max single runlength is 63 */
  total = 0;
  runCount = 1;
  last = *(inBuff);
/* Find the pixel dimensions of the image by calculating 
[XSIZE = Xmax - Xmin + 1] and [YSIZE = Ymax - Ymin + 1].  
Then calculate how many bytes are in a "run" */
  for (srcIndex = 1; srcIndex < inLen; srcIndex++)
	this = *(++inBuff);
	if (this == last)     /* There is a "run" in the data, encode it */
		if (runCount == 63)
			if (! (i = encput(last, runCount, fp)))
				return (0);
			total += i;
			runCount = 0;
	else		/* No "run"  -  this != last */
		if (runCount)
			if (! (i = encput(last, runCount, fp)))
			total += i;
		last = this;
		runCount = 1;
	}	/* endloop */
  if (runCount)	/* finish up */
	if (! (i = encput(last, runCount, fp)))
		return (0);
	return (total + i);
  return (total);

FRIEZE Technical Information

General FRIEZE Information

FRIEZE is a memory-resident utility that allows you to capture and save
graphic images from other programs.  You can then bring these images
into PC Paintbrush for editing and enhancement.

FRIEZE 7.10 and later can be removed from memory (this can return you up
to 90K of DOS RAM, depending on your configuration). To remove FRIEZE
from memory, change directories to your paintbrush directory and type
the word "FRIEZE".

7.00 and Later FRIEZE

The FRIEZE command line format is:
FRIEZE {PD} {Xn[aarr]} {flags} {video} {hres} {vres} {vnum}
{PD}	Printer driver filename (without the .PDV extension)
		X=S for Serial Printer, P for Parallel Printer, D for
                        disk file.  (file is always named FRIEZE.PRN)
		n = port number
		aa = Two digit hex code for which return bits cause
			 an abort (optional)
		rr = Two digit hex code for which return bits cause
			a retry (optional)
		NOTE:  These codes represent return values from serial or
                       parallel port  BIOS calls.  For values see and IBM
                       BIOS reference (such as Ray Duncan's Advanced
                       MS-DOS Programming).
{flags}Four digit hex code
	First Digit controls Length Flag
	Second Digit controls Width Flag
		Third Digit controls Mode Flag
		Fourth Digit controls BIOS Flag
			0 - None
			1 - Dual Monitor Present
			2 - Use internal (true) B/W palette for dithering
				2 color images
			4 - Capture palette along with screen IN VGA ONLY
				Frieze 8.08 & up ONLY)

NOTE:	The length, width and mode flags are printer driver specific.
See PRINTERS.DAT on disk 1 (or Setup Disk) for correct use.  In general
width flag of 1 means wide carriage, and 0 means standard width.  Length
flag of 0 and mode flag of 0 means use default printer driver settings.

If you need to use more than one BIOS flag option, add the needed flag
values and use the sum as the flag value.

{video} Video driver combination, where the leading digit signifies the
high level video driver and the rest signifies the low level video
		Example = 1EGA - uses DRIVE1 and EGA.DEV
{hres}	Horizontal resolution of the desired graphics mode
{vres}	Vertical resolution of the desired graphics mode
{vnum}	Hardware specific parameter (usually number of color planes)
Note: The last four parameters can be obtained from the CARDS.DAT file,
in your PC Paintbrush product directory.

FRIEZE Function Calls

FRIEZE is operated using software interrupt number 10h (the video
interrupt call).

To make a FRIEZE function call, load 75 (decimal) into the  AH register
and the function number into the CL register, then either load AL with
the function argument or load ES and BX with a segment and offset which
point to the function argument. Do an int 10h. FRIEZE will return a
result code number in AX.  All other registers are preserved.  In
general, a result code of 0 means success and other values indicate
errors.  However, function 20 (get Frieze Version) behaves differently;
see below.

No.	Definition 	Arguments
0	Reserved
1	Load Window
	ES:BX - string  (filename to read from)
2	Save Window
	ES:BX - string  (filename to write to)
3	Reserved
4	Reserved	
6	Reserved	
7	Set Window Size
	ES:BX - 4 element word vector of window settings:
	Xmin, Ymin, Xmax, Ymax
8	Reserved
9	Set Patterns	
	ES:BX - 16 element vector of byte values containing the
	screen-to-printer color correspondence
10	Get Patterns
	ES:BX - room for 16 bytes as above
11	Set Mode
12, 13, 14	Reserved
15	Get Window
	ES:BX - room for 4 words of the current window settings
16 	Set Print Options
	ES:BX - character string of printer options.
	Same format as for the FRIEZE command.
17, 18, 19	Reserved
20	Get FRIEZE Version.
	AH gets the whole number portion and AL gets the decimal portion of
	the version number.  (eg. for Freize vesion 7.41, AH will contain 7 and
	AL will contain 41.  If AH =0, you are calling a pre-7.0 version of FRIEZE).
21	Set Parameters
	ES:BX points to an 8 word table  (16 bytes) of parameter settings: 
	TopMargin, LeftMargin, HSize,VSize, Quality/Draft Mode, PrintHres, 
	PrintVres, Reserved.
	Margins and sizes are specified in hundredths  of inches.
		Q/D mode parameter values:
		0 - draft print mode
		1 - quality print mode
		Print resolutions are specified in DPI.
	Any parameter which should be left unchanged may be filled with
	a (-1) (0FFFF hex).  The reserved settings should be filled with a (-1).
22	Get Parameters
	ES:BX points to an 8 word table  (16 bytes) where parameter settings
	are held.
23	Get Printer Res
	ES:BX points to a 12 word table (24 bytes) that holds six printer
	resolution pairs.
24	Reserved (versions 8.00 & up)

FRIEZE Error Codes

When FRIEZE is called using interrupt 10 hex, it will return an error
code in the AX register.  A value of zero shows that there was no error.
A nonzero result means there was an error.  These error codes are
explained below.

0	No Error
1	Printout was stopped by user with the ESC key
2	Reserved
3	File read error
4	File write error
5	File not found
6	Invalid Header - not an image, wrong screen mode
7	File close error
8	Disk error - usually drive door open
9	Printer error - printer is off or out of paper
10	Invalid command - CL was set to call a nonexistent  FRIEZE function
11	Can't create file - write protect tab or disk is full
12	Wrong video mode - FRIEZE cannot capture text screens.
Technical Reference Manual

Including information for:
Publisher's Paintbrushr
PC Paintbrush IVTM
PC Paintbrush IV PlusTM
PC Paintbrush PlusTM
PC Paintbrushr
Revision 4

ZSoft Corporation
450 Franklin Rd. Suite 100
Marietta, GA  30067
(404) 428-0008
(404) 427-1150 Fax
(404) 427-1045 BBS

Copyright c 1985, 1987, 1988, 1990, ZSoft Corporation   All Rights Reserved