Path: utzoo!mnetor!uunet!husc6!think!ames!pasteur!ucbvax!TIS.COM!dmb
From: dmb@TIS.COM (David M. Baggett)
Newsgroups: comp.sys.atari.st
Subject: Picture Formats!!
Message-ID: <8805031609.AA01371@TIS.COM>
Date: 3 May 88 16:09:43 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 184


   A while back I asked about picture formats.  Thanks to all who responded.
Since *lots* of people have being asking about formats, I compiled all
the format descriptions and rewrote them.  Hopefully, they're coherent and
correct.  Please report errors in the file to me (dmb@tis.com). 
   Here 'tis:

---------------------------Cut Here----------------------------------------
                           ST Picture Formats
                           ------------------

                        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)


                             The Formats


<NEOChrome>

1 long		resolution (0 = low res, 1 = medium res, 2 = high res)
16 words	palette
12 bytes	filename ("        .   ")
1 byte		Left color animation limit (starting color number)
1 byte	 	Right color animation limit (ending color number)
1 byte		color rotation speed
1 byte		color rotation direction
1 word		color rotation duration (number of iterations)
18 longs	reserved for expansion
16000 words 	picture data (screen memory)
-----------
32128 bytes	total


<DEGAS>

1 word 		resolution (0 = high res, 1 = medium res, 2 = low res)
16 words	palette
16000 words	picture data (screen memory)
-----------
32034 bytes	total


<DEGAS Elite>

1 word 		resolution (0 = high res, 1 = medium res, 2 = low res)
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		animation channel delay in 1/60's of a second. [0 - 128] 
-----------
32066 bytes	total


<C.O.L.R. Object Editor Mural>

16000 words	picture data (screen memory)
-----------
32000 bytes	total


<Tiny>

1 byte		resolution (same as NEO, but +3 indicates rotation 
		information 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)
}

1 word		number of control bytes
1 word		number of data bytes
16 words	palette
3-10667 bytes	control bytes
2-32000 bytes	data bytes
-------------
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 long 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)
		

<Spectrum 512 (Uncompressed)>

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


<Spectrum 512 (Compressed)>

1 word		5350 (hex) ("SP")
1 word		0 (reserved for future use)
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.  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 < 0	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 decompression:

   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; i.e., stays
the same).  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).


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