Changes between Initial Version and Version 1 of Develop/FileFormats/Atari

Timestamp:

Oct 8, 2016, 1:36:40 PM (8 years ago)

Author:

pulkomandy

Comment:

--

Develop/FileFormats/Atari

@@ +1 @@
+This is a copy of the document "ST Picture Formats" : [http://www.umich.edu/~archive/atari/Graphics/picfmts.doc picfmts.doc]
+
+We use it as a reference for implementing NEOchrome images support.
+
+The original document is enclosed in tags to prevent wiki formatting, but otherwise unmodified.
+
+{{{
+                           ST Picture Formats
+                           ------------------
+                               Edited by:
+
+                              David Baggett
+                         5640 Vantage Point Road
+                         Columbia, MD  21044 USA
+                             (301)  596-4779    
+                          (usenet: dmb@TIS.COM)
+
+                   (Please report errors or additions.)
+
+        Copyright (C) 1988, 1989, 1990, 1991 by David M. Baggett
+
+
+    Non-profit redistribution of this document is permitted, provided
+    the document is not modified in any way.
+
+    Reproduction of this document in whole or in part for  commercial
+    purposes is expressly forbidden without the prior written consent
+    of David M. Baggett.
+
+    The  information  presented here is not guaranteed to be correct.
+    The editor and contributors will in no event be liable for direct,
+    indirect, incidental, or consequential damages resulting from the 
+    use of the information in this document.
+
+    This document is the product of many hours of volunteer work by a
+    large number of people. Please respect this -- do not violate the
+    distribution policy.
+
+
+                              CONTRIBUTORS
+  
+    Steve Belczyk  Phil Blanchfield  Jason Blochowiak  John Brochu**
+       David Brooks  Daniel Deimert  Neil Forsyth   Stefan Hoehn  
+        Gerfried Klein   Ken MacLeod  Jim McCabe  Darek Mihocka   
+         David Mumper   George Nassas   George Seto  Joe Smith  
+              Greg Wageman   Roland Waldi*  Gerry Wheeler
+
+
+                                Contents 
+                                --------
+
+        NEOchrome                               *.NEO
+        NEOchrome Animation                     *.ANI
+        DEGAS                                   *.PI?   ? = 1, 2, 3
+        DEGAS Elite                             *.PI?   ? = 1, 2, 3
+        DEGAS Elite (Compressed)                *.PC?   ? = 1, 2, 3
+        Tiny                                    *.TN?   ? = 1, 2, 3, Y
+        Spectrum 512                            *.SPU
+        Spectrum 512 (Compressed)               *.SPC
+        Art Director                            *.ART
+        C.O.L.R. Object Editor Mural            *.MUR
+        Doodle                                  *.DOO
+        Animatic Film                           *.FLM
+        GEM Bit Image                           *.IMG
+        STAD                                    *.PAC
+        Imagic Film/Picture                     *.IC?   ? = 1, 2, 3
+        IFF                                     *.IFF
+        MacPaint                                *.MAC
+        PackBits Compression Algorithm
+ 
+
+                        Introductory Information
+                        ------------------------
+word    = 2 bytes
+long    = 4 bytes
+palette = Hardware color palette, stored as 16 words.  First word is
+          color register zero (background), last word is color register
+          15.  Each word has the form:
+
+          Bit:  (MSB) 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 (LSB)
+                      -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+                       0  0  0  0  0 R2 R1 R0  0 G2 G1 G0  0 B2 B1 B0
+
+          R2 = MSB of red intensity
+          R0 = LSB of red intensity
+
+          G2 = MSB of green intensity
+          G0 = LSB of green intensity
+
+          B2 = MSB of blue intensity
+          B0 = LSB of blue intensity
+
+          Intensity ranges from 0 (color not present) to 7 (highest
+          intensity).
+
+          Example: { red = 7, green = 3, blue = 5 } -> 0735 (hex)
+
+          Caveat:  It is wise to mask off the upper four bits of each
+                   palette entry, since a few programs store special
+                   information there (most notably Art Studio).
+
+
+                             The Formats
+                             -----------
+
+<NEOchrome>     *.NEO
+ 
+1 word          flag byte [always 0]
+1 word          resolution [0 = low res, 1 = medium res, 2 = high res]
+16 words        palette
+12 bytes        filename [usually "        .   "]
+1 word          color animation limits.  High bit (bit 15) set if color
+                animation data is valid.  Low byte contains color animation
+                limits (4 most significant bits are left/lower limit,
+                4 least significant bits are right/upper limit).
+1 word          color animation speed and direction.  High bit (bit 15) set
+                if animation is on.  Low order byte is # vblanks per step.
+                If negative, scroll is left (decreasing).  Number of vblanks
+                between cycles is |x| - 1
+1 word          # of color steps (as defined in previous word) to display
+                picture before going to the next.  (For use in slide shows)
+1 word          image X offset [unused, always 0]
+1 word          image Y offset [unused, always 0]
+1 word          image width [unused, always 320]
+1 word          image height [unused, always 200]
+33 words        reserved for future expansion
+16000 words     picture data (screen memory)
+-----------
+32128 bytes     total
+ 
+
+<NEOchrome Animation>        *.ANI
+
+NOTE:      To get this feature on versions 0.9 and later select the Grabber
+        icon and click both mouse buttons in the eye of the second R in the
+        word GRABBER.
+           Interestingly enough, some versions of NEO only require you
+        to press the right button, not both.  Hmmm...
+
+1 long          magic number BABEEBEA (hex) (seems to be ignored)
+1 word          width of image in bytes (always divisible by 8)
+1 word          height of image in scan lines
+1 word          size of image in bytes + 10 (!)
+1 word          x coordinate of image (must be divisible by 16) - 1
+1 word          y coordinate of image - 1
+1 word          number of frames
+1 word          animation speed (# vblanks to delay between frames)
+1 long          reserved; should be zero
+--------
+22 bytes        total for header
+
+? words         image data (words of screen memory) for each frame, in 
+                order
+
+
+<DEGAS>         *.PI1 (low resolution)
+                *.PI2 (medium resolution)
+                *.PI3 (high resolution)
+
+1 word          resolution (0 = low res, 1 = medium res, 2 = high res)
+                Other bits may be used in the future; use a simple bit
+                test rather than checking for specific word values.
+16 words        palette
+16000 words     picture data (screen memory)
+-----------
+32034 bytes     total
+
+
+<DEGAS Elite>   *.PI1 (low resolution)
+                *.PI2 (medium resolution)
+                *.PI3 (high resolution)
+
+1 word          resolution (0 = low res, 1 = medium res, 2 = high res)
+                Other bits may be used in the future; use a simple bit
+                test rather than checking for specific word values.
+16 words        palette
+16000 words     picture data (screen memory)
+4 words         left color animtion limit table (starting color numbers)
+4 words         right color animation limit table (ending color numbers)
+4 words         animation channel direction flag (0 = left, 1 = off, 2 = right)
+4 words         128 - animation channel delay in 1/60's of a second. [0 - 128]
+                (I.e., subtract word from 128 to get 1/60th's of a second.)
+-----------
+32066 bytes     total
+
+
+<DEGAS Elite (Compressed)>      *.PC1 (low resolution)
+                                *.PC2 (medium resolution)
+                                *.PC3 (high resolution)
+ 
+1 word          resolution (same as Degas, but high order bit is set;
+                i.e., hex 8000 = low res, hex 8001 = medium res,
+                hex 8002 = high res).  Other bits may be used in the
+                future; use a simple bit test rather than checking
+                for specific word values.
+16 words        palette
+< 32000 bytes   control/data bytes
+4 words         left color animation limit table (starting color numbers)
+4 words         right color animation limit table (ending color numbers)
+4 words         animation channel direction flag [0 = left, 1 = off, 2 = right]
+4 words         128 - animation channel delay in 1/60's of a second. [0 - 128]
+                (I.e., subtract word from 128 to get 1/60th's of a second.)
+-----------
+< 32066 bytes   total
+ 
+Compression Scheme:
+ 
+   PackBits compression is used (see below).  Each scan line is compressed
+separately; i.e., all data for a given scan line appears before any data
+for the next scan line.  The scan lines are specified from top to bottom
+(i.e., 0 is first).  For each scan line, all the data for a given bit plane
+appears before any data for the next higher order bit plane.  Note this is
+identical to the IFF 'BODY' image data.
+   To clarify:  The first data in the file will be the data for the lowest
+order bit plane of scan line zero, followed by the data for the next higher
+order bit plane of scan line zero, etc., until all bit planes have been
+specified for scan line zero.  The next data in the file will be the data
+for the lowest order bit plane of scan line one, followed by the data for
+the next higher order bit plane of scan line one, etc., until all bit planes
+have been specified for all scan lines.
+ 
+Caveats:
+ 
+   DEGAS Elite's picture loading routine places some restrictions on
+compressed DEGAS files:
+ 
+        o Elite uses a 40-byte buffer to store data being decompressed.
+ 
+        o Whenever a control command is encountered, bytes are stuffed
+        in this buffer.
+ 
+        o The buffer is only emptied when there are EXACTLY 40
+        characters in it.
+ 
+The important conclusion here is that
+ 
+        No control command may cause the buffer to have more than 40
+        bytes in it.  In other words, all control commands must end on
+        or before the 40-byte boundary.
+ 
+Any picture violating the last condition will cause Elite to get a bus
+error when the picture is loaded.
+ 
+
+<Tiny>  *.TNY (any resolution)
+        *.TN1 (low resolution)
+        *.TN2 (medium resolution)
+        *.TN3 (high resolution)
+
+   Several people have reported sightings of mutated Tiny pictures that
+do not follow the standard format, so let's be careful out there.  What
+is described here is the format that David Mumper's original
+TNYSTUFF.PRG produces.
+
+1 byte          resolution (same as NEO, but +3 indicates rotation
+                information also follows)
+
+If resolution > 2 {
+1 byte          left and right color animation limits.  High 4 bits
+                hold left (start) limit; low 4 bits hold right (end)
+                limit
+1 byte          direction and speed of color animation (negative value
+                indicates left, positive indicates right, absolute value
+                is delay in 1/60's of a second.
+1 word          color rotation duration (number of iterations)
+}
+
+16 words        palette
+1 word          number of control bytes
+1 word          number of data words
+3-10667 bytes   control bytes
+1-16000 words   data words
+-------------
+42-32044 bytes  total
+
+Control byte meanings:
+
+        For a given control byte, x:
+
+        x < 0   Absolute value specifies the number of unique words to
+                take from the data section (from 1 to 127)
+        x = 0   1 word is taken from the control section which specifies
+                the number of times to repeat the next data word (from
+                128 to 32767)
+        x = 1   1 word is taken from the control section which specifies
+                the number of unique words to be taken from the data
+                section (from 128 - 32767)
+        x > 1   Specifies the number of times to repeat the next word
+                taken from the data section (from 2 to 127)
+
+Format of expanded data:
+
+   The expanded data is not simply screen memory bitmap data; instead, the 
+data is divided into four sets of vertical columns.  (This results in
+better compression.)  A column consists of one specific word taken
+from each scan line, going from top to bottom.  For example, column 1 
+consists of word 1 on scanline 1 followed by word 1 on scanline 2, etc., 
+followed by word 1 on scanline 200.
+   The columns appear in the following order:
+
+   1st set contains columns 1, 5,  9, 13, ..., 69, 73, 77 in order
+   2nd set contains columns 2, 6, 10, 14, ..., 70, 74, 78 in order
+   3rd set contains columns 3, 7, 11, 15, ..., 71, 75, 79 in order
+   4th set contains columns 4, 8, 12, 16, ..., 72, 76, 80 in order
+
+Note that Tiny partitions the screen this way regardless of resolution; i.e., 
+these aren't bitplanes.  For example, medium resoltion only has two bitplanes, 
+but Tiny still divides medium resolution pictures into four parts.
+
+
+<Spectrum 512>  *.SPU
+
+80 words        first scan line of picture (unused) -- should be zeroes
+15920 words     picture data (screen memory) for scan lines 1 through 199
+9552 words      3 palettes for each scan line (the top scan line is
+                not included because Spectrum 512 can't display it)
+-----------
+51104 bytes     total
+
+Note that the Spectrum 512 mode's three palette changes per scan
+line allow more colors on the screen than normally possible, but a
+tremendous amount of CPU time is required to maintain the image.
+
+The Spectrum format specifies a palette of 48 colors for each scan line.
+To decode a Spectrum picture, one must be know which of these 48 colors
+are in effect for a given horizontal pixel position.
+
+Given an x-coordinate (from 0 to 319) and a color index (from 0 to 15),
+the following C function will return the proper index into the Spectrum
+palette (from 0 to 47):
+
+/*
+ *  Given an x-coordinate and a color index, returns the corresponding
+ *  Spectrum palette index.
+ *
+ *  by Steve Belczyk; placed in the public domain December, 1990.
+ */
+int 
+FindIndex(x, c)
+        int x, c;
+{
+        int x1;
+
+        x1 = 10 * c;
+
+        if (1 & c)              /* If c is odd */
+                x1 = x1 - 5;
+        else                    /* If c is even */
+                x1 = x1 + 1;
+
+        if (x >= x1 && x < x1 + 160) 
+                c = c + 16;
+        else if (x >= x1 + 160) 
+                c = c + 32;
+
+        return c;
+}
+
+
+<Spectrum 512 (Compressed)>        *.SPC
+ 
+1 word          flag word [$5350 or "SP"]
+1 word          reserved for future use [always 0]
+1 long          length of data bit map
+1 long          length of color bit map
+<= 32092 bytes  compressed data bit map
+<= 17910 bytes  compressed color bit map
+--------------
+<= 50014 bytes   total
+ 
+Data compression:
+ 
+   Compression is via a modified run length encoding (RLE) scheme,
+similar to DEGAS compressed and Tiny.  The data map is stored as a
+sequence of records.  Each record consists of a header byte followed by
+one or more data bytes.  The meaning of the header byte is as follows:
+ 
+        For a given header byte, x:
+ 
+           0 <= x <= 127   Use the next x + 1 bytes literally (no repetition)
+        -128 <= x <=  -1   Use the next byte -x + 2 times
+ 
+The data appears in the following order:
+ 
+        1. Picture data, bit plane 0, scan lines 1 - 199
+        2. Picture data, bit plane 1, scan lines 1 - 199
+        3. Picture data, bit plane 2, scan lines 1 - 199
+        4. Picture data, bit plane 3, scan lines 1 - 199
+ 
+Decompression of data ends when 31840 data bytes have been used.
+ 
+Color map compression:
+ 
+   Each 16-word palette is compressed separately.  There are three
+palettes for each scan line (597 total).  The color map is stored as a
+sequence of records.  Each record starts with a 1-word bit vector which
+specifies which of the 16 palette entries are included in the data
+following the bit vector (1 = included, 0 = not included).  If a palette
+entry is not included, it is assumed to be zero (black).  The least
+significant bit of the bit vector refers to palette entry zero, while the
+most significant bit refers to palette entry 15.  Bit 15 must be zero,
+since Spectrum 512 does not use palette entry 15.  Bit 0 should also be
+zero, since Spectrum 512 always makes the background color black.
+   The words specifying the values for the palette entries indicated in
+the bit vector follow the bit vector itself, in order (0 - 15).
+
+
+<Art Director>  *.ART (low resolution only)
+
+16000 words     picture data (screen memory)
+16 words        palette
+15 * 16 words   15 more palettes for animation
+-------------
+32512 bytes     total
+
+
+<C.O.L.R. Object Editor Mural>        *.MUR (low resolution only)
+
+16000 words     picture data (screen memory)
+                (palettes are stored in separate files)
+-----------
+32000 bytes     total
+
+
+<Doodle>        *.DOO (high resolution only)
+
+16000 words     picture data (screen memory)
+-----------
+32000 bytes     total
+
+
+<Animatic Film> *.FLM (low resolution only)
+
+1 word          number of frames
+16 words        palette
+1 word          speed (0 - 99; value is 99 - # vblanks to delay between frames)
+1 word          direction (0 = forwards, 1 = backwards)
+1 word          end action (what to do after the last frame)
+                0 = pause, then repeat from beginning
+                1 = immediately repeat from beginning
+                2 = reverse (change direction)
+1 word          width of film in pixels
+1 word          height of film in pixels
+1 word          Animatic version number (major)
+1 word          Animatic version number (minor)
+1 long          magic number 27182818 (hex)
+3 longs         reserved for expansion (should be all zeros)
+--------
+32 words        total for header
+
+? words         image data (words of screen memory) for each frame, in order
+
+
+<GEM Bit Image> *.IMG
+ 
+1 word          version number of image file [1]
+1 word          length of header in words [usually 8]
+1 word          number of color planes [1 for monochrome]
+1 word          pattern length in bytes [1-8, usually 2 for screen images]
+1 word          pixel width in microns (1/1000 mm, 25400 microns per inch)
+1 word          pixel height in microns
+1 word          line width in pixels
+1 word          number of lines
+-------
+? words         header length defined in 2nd word of header
+ 
+? bytes         data
+ 
+NOTES:  If the image is a color image (planes > 1), the planes are stored
+separately starting with plane 0.  There is, however, no standard way of
+storing the color palette.  Some programs may save the palette in separate
+files, some may extend the header.  For this reason, you should never
+assume the header is 8 words long, always get the header length from the
+2nd word of the header.  Also, the line width in the 7th word is the number
+of pixels in a line.  Since the data is encoded in byte-wide packets, the
+actual unpacked line width is always a multiple of 8, and may be 1-7 pixels
+longer than the length specified in the header.
+
+For each byte x in the data section,
+ 
+        x = 0           Pattern/scanline run.
+                        Read the next byte, n (unsigned).
+ 
+                        If n > 0 then:
+                                Read a number of bytes equal to the "pattern
+                                length" word in the header.  Repeat this
+                                pattern n times.
+ 
+                        If n = 0 then:
+                                Scanline run.  Data for the next scanline
+                                is to be used multiple times.  Read the
+                                following record:
+ 
+                                1 byte          flag byte [$FF]
+                                1 byte          number of times to use
+                                                next scanline data
+ 
+                                The data for the next scanline follows,
+                                compressed normally.
+ 
+        x = 80 (hex)    Uncompressed bit string.  The next byte
+                        determines the number of bytes to use
+                        literally.  The literal data bytes follow.
+ 
+        otherwise       Solid run.  The value of x determines
+                        what to draw.  The high bit specifies whether
+                        the pixels are set or cleared.  A 1 indicates
+                        a byte-run using $FF, a 0 indicates a byte-run
+                        using $00.  The low 7 bits, taken as an unsigned
+                        quantity, specify the length of the run in bytes.
+ 
+
+<STAD>          *.PAC (high resolution only)
+
+4 bytes         "pM86" (vertically packed) or "pM85" (horizontally packed)
+1 byte          id byte
+1 byte          pack byte (most frequently occuring byte in bitmap)
+1 byte          "special" byte
+-------
+7 bytes         total for header
+
+? bytes         data
+
+The data is encoded as follows.  For each byte x in the data section:
+
+        x = id byte             Read one more byte, n.  Use pack byte 
+                                n + 1 times.
+        x = "special" byte      Read two more bytes, d, and n (in order).
+                                Use byte d n times.
+        otherwise               Use byte x literally.
+
+
+<Imagic Film/Picture>           *.IC1 (low resolution)
+                                *.IC2 (medium resolution)
+                                *.IC3 (high resolution)
+
+4 bytes         "IMDC"
+1 word          resolution (0 = low res, 1 = medium res, 2 = high res)
+16 words        palette
+1 word          date (GEMDOS format)
+1 word          time (GEMDOS format)
+8 bytes         name of base picture file (for delta compression), or zeroes
+1 word          length of data (?)
+1 long          registration number
+8 bytes         reserved
+1 byte          compressed? (0 = no, 1 = yes)
+
+If compressed {
+1 byte          delta-compressed? (-1 = no, > -1 = yes)
+1 byte          ?
+1 byte          escape byte
+}
+-------
+65 bytes        total for header (68 bytes if compressed)
+
+? bytes         data
+
+   Compressed data may be either stand-alone or delta-compressed (relative
+to the base picture named in the header).  Delta compression involves
+storing only how the picture differs from the base picture (i.e., only
+portions of the screen that have changed are stored).  This is used to
+to encode animated sequences efficiently.
+
+Compressed data, stand-alone:
+
+For each byte x in the data section:
+
+        x = escape byte         Read one more byte, n.  (n is unsigned).
+
+                                If n >= 2, use the next byte n times.
+                                If n = 1, keep reading bytes until a
+                                byte k not equal to 1 is encountered.
+                                Then read the next byte d.
+                                If the number of 1 bytes encountered is o,
+                                use d (256 * o + k) times.  I.e.,
+
+                                if (n == 1) {
+                                        o = 0;
+                                        while (n == 1) {
+                                                o++;
+                                                n = next byte;
+                                        }
+
+                                        k = n;
+                                        d = next byte;
+
+                                        Use d (256 * o + k) times.
+                                }
+                                else {
+                                        d = next byte;
+                                        Use d (n) times.
+                                }
+
+        x != escape byte        Use x literally.
+
+Compressed data, delta compressed:
+
+For each byte x in the data section:
+
+        x = escape byte         Read one more byte, n.  (n is unsigned).
+
+                                If n >= 3, use the next byte n times.
+                                If n = 1, do the same as for n = 1 in
+                                stand-alone compression (above).
+                                If n = 2, then set n = next byte.
+                                        If n = 0, end of picture.
+                                        If n >= 2, take n bytes from base
+                                        picture.
+                                        If n = 1, do the same as for n = 1
+                                        in stand-alone compression (above),
+                                        but take (256 * o + k) bytes from 
+                                        base picture.
+
+        x != escape byte        Use x literally.
+
+
+<IFF Format>    *.IFF
+ 
+4 bytes         "FORM" (FORM chunk ID)
+1 long          length of file that follows
+4 bytes         "ILBM" (InterLeaved BitMap file ID)
+
+4 bytes         "BMHD" (BitMap HeaDer chunk ID)
+1 long          length of chunk [20]
+20 bytes        1 word = image width in pixels
+                1 word = image height in lines
+                1 word = image x-offset [usually 0]
+                1 word = image y-offset [usually 0]
+                1 byte = # bitplanes
+                1 byte = mask (0=no, 1=impl., 2=transparent, 3=lasso)
+                1 byte = compressed [1] or uncompressed [0]
+                1 byte = unused [0]
+                1 word = transparent color (for mask=2)
+                1 byte = x-aspect [5=640x200, 10=320x200/640x400, 20=320x400]
+                1 byte = y-aspect [11]
+                1 word = page width (usually the same as image width)
+                1 word = page height (usually the same as image height)
+
+4 bytes         "CMAP" (ColorMAP chunk ID)
+1 long          length of chunk [3*n where n is the # colors]
+3n bytes        3 bytes per RGB color.  Each color value is a byte
+                and the actual color value is left-justified in the
+                byte such that the most significant bit of the value
+                is the MSB of the byte.  (ie. a color value of 15 ($0F)
+                is stored as $F0)  The bytes are stored in R,G,B order.
+
+4 bytes         "CRNG" (Color RaNGe chunk ID)
+1 long          length of chunk [8]
+8 bytes         1 word = reserved [0]
+                1 word = animation speed (16384 = 60 steps per second)
+                1 word = active [1] or inactive [0]
+                1 byte = left/lower color animation limit
+                1 byte = right/upper color animation limit
+
+4 bytes         "CAMG" (Commodore AMiGa viewport mode chunk ID)
+1 long          length of chunk [4]
+1 long          viewport mode bits (bit 11 = HAM, bit 3 = interlaced)
+
+4 bytes         "BODY" (BODY chunk ID)
+1 long          length of chunk [# bytes of image data that follow]
+? bytes         actual image data
+ 
+NOTES: Some of these chunks may not be present in every IFF file, and may
+not be in this order.  You should always look for the ID bytes to find a
+certain chunk.  All chunk IDs are followed by a long value that tells the
+size of the chunk.  This is the number of bytes that FOLLOW the 4 ID bytes
+and size longword.  The exception to this is the FORM chunk.  The size
+longword that follows the FORM ID is the size of the remainder of the file.
+The FORM chunk must always be the first chunk in an IFF file.
+
+The R,G,B ranges of AMIGA and ST are different (AMIGA 0...15, ST 0...7),
+as is the maximum number of bitplanes (AMIGA: 5, ST: 4).
+
+Format of body data
+ 
+An expanded picture is simply a bitmap.  The packing method is PackBits
+(see below), and is identical to MacPaint and DEGAS Elite compressed.
+ 
+The (decompressed) body data appears in the following order:
+ 
+        line 1 plane 0 ... line 1 plane 1 ... ... line 1 plane m
+        [line 1 mask (if appropriate)]
+        line 2 plane 0 ... line 2 plane 1 ... ... line 2 plane m
+        [line 2 mask (if appropriate)]
+        ...
+        line x plane 0 ... line x plane 1 ... ... line x plane m
+        [line x mask (if appropriate)]
+ 
+The FORM chunk identifies the type of data:
+ 
+        "ILBM" = interleaved bit map
+        "8SVX" = 8-bit sample voice
+        "SMUS" = simple music score
+        "FTXT" = formatted text (Amiga)
+ 
+
+<MacPaint>      *.MAC
+ 
+1 long          version number [0=ignore header, 2=header valid]
+38 * 8 bytes    8x8 brush/fill patterns.  Each byte is a pattern row,
+                and the bytes map the pattern rows top to bottom.  The
+                patterns are stored in the order they appear at the bottom
+                of the MacPaint screen top to bottom, left to right.
+204 bytes       unused
+-------------
+512 bytes       total for header
+
+< 51200 bytes   compressed bitmap data
+-------------
+< 51712 bytes   total
+ 
+NOTE:  The version number is actually a flag to MacPaint to indicate if
+the brush/fill patterns are present in the file.  If the version is 0,
+the default patterns are used.  Therefore you can simply save a MacPaint
+file by writing a blank header (512 $00 bytes), followed by the packed
+image data.
+
+Bitmap compression:
+ 
+   The bitmap data is for a 576 pixel by 720 pixel monochrome image.
+The packing method is PackBits (see below).  There are 72 bytes per
+scan line.  Each bit represents one pixel; 0 = white, 1 = black.
+ 
+
+<PackBits Compression Algorithm>
+
+The following packing algorithm originated on the Mac, was adopted by
+Electronic Arts/Commodore for use in the IFF standard, and then by Tom
+Hudson for use in DEGAS Elite.  The algorithm is currently used in
+MacPaint, IFF, and DEGAS Elite compressed file formats.  Each scan line
+is packed separately, and packing never extends beyond a scan line.
+
+For a given control byte 'n':
+    0 <= n <= 127   : use the next n + 1 bytes literally (no repetition).
+ -127 <= n <= -1    : use the next byte -n + 1 times.
+         n = -128   : no operation, not used.
+
+-------------------------------------------------------------------------
+
+* Roland Waldi contributed extensive information on the following formats:
+
+        GEM, IMG, Doodle, STAD, Imagic Film/Picture, Art Director, IFF
+
+** John Brochu, ST picture formats guru, provided sage advice and many
+   corrections to the following formats:
+
+        NeoChrome, DEGAS Elite Compressed, Spectrum 512 Compressed,
+        GEM Bit Image, IFF, MacPaint
+
+Version of Wed Dec 19 11:20:55 EST 1990
+Cosmetic changes Tue Jan 29 00:17:51 EST 1991
+}}}