ZSoft PCX File Format Technical Reference Manual
Part of "The QB Times issue 4 and 5"
Contents
- Introduction
- Image File (.PCX) Format
- ZSoft .PCX FILE HEADER FORMAT
- Decoding .PCX Files
- Palette Information Description
- EGA/VGA 16 Color Palette Information
- VGA 256 Color Palette Information
- 24-Bit .PCX Files
- CGA Color Palette Information
- CGA Color Map
- PC Paintbrush Bitmap Character Format
- Sample "C" Routines
- FRIEZE Technical Information
- General FRIEZE Information
- 7.00 and Later FRIEZE
- FRIEZE Function Calls
- FRIEZE Error Codes
Introduction
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 to:
ZSoft Corporation
Technical Services
ATTN: Code Librarian
450 Franklin Rd. Suite 100
Marietta, GA 30067
Technical Reference Manual information compiled by: 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: RRR...
GGG...
BBB...
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
ELSE
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.
ZSoft .PCX FILE HEADER FORMAT
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
NOTES:
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
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 |
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 4.
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 palette.
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.
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 follows:
- 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:
Header
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 file.
/* 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))
break;
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) */
return(1);
}
else
{
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 */
{
runCount++;
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)))
return(0);
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}
Where:
{PD} Printer driver filename (without the .PDV extension)
{Xn[aarr]}
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 driver 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
FRIEZETM Graphics
PaintbrushTM
Revision 5
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, 1991, ZSoft Corporation
All Rights Reserved
