Encyclopedia of Graphics File Formats Companion/GFF_CD.ISO/formats/pcx/spec/pcx.txt

Text File | 1994-06-20 | 20KB | 564 lines

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
[phone]
[phone] Fax
[phone] BBS

Copyright c 1985, 1987, 1988, 1990, 1991, ZSoft Corporation
All Rights Reserved


Technical Reference Manual

Introduction     2
Image  File (.PCX) Format     3
ZSoft .PCX FILE HEADER FORMAT     4
Decoding .PCX Files     6
Palette Information Description     7
EGA/VGA 16 Color Palette Information     7
VGA 256 Color Palette Information     7
24-Bit .PCX Files     8
CGA Color Palette Information     8
CGA Color Map     8
PC Paintbrush Bitmap Character Format     9
Sample "C" Routines     10
FRIEZE Technical Information     14
General FRIEZE Information     14
7.00 and Later FRIEZE     14
FRIEZE Function Calls     15
FRIEZE Error Codes     18




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 [phone].  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.