>Lp: add link to asm code

2017-01-14T22:31:13Z

add link to asm code

← Older revision		Revision as of 18:31, 14 January 2017
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	x != escape byte Use x literally.		x != escape byte Use x literally.

			Note: 68K decompression code can be found here:
			http://gfa.atari-users.net/gfx/
	</pre>		</pre>
	Back to [[ST Picture Formats]]		Back to [[ST Picture Formats]]

>Lp: New page

2017-01-03T00:18:04Z

New page

New page

<pre>
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.
</pre>
Back to [[ST Picture Formats]]

Imagic Film/Picture file format - Revision history

>Lp: add link to asm code

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