This is my attempt to describe how some of the Atari versions of the SAGA images were formed.
Note, I have taken this information from only a few games (the few Atari ones I've been able to find).
If you have any Atari versions of the other SAGA games I would like to see them so I can ensure that
my routines work on all of them. The games I used are:
The Atari games come on two discs, the first disc contains the machine code and the
game data. The second disc just seems to contain graphic data, with a small initial boot
sector to tell somebody booting from that disc to use the other disc.
The discs aren't read as files - just directly read from the disc; so we can treat
the whole disc as a data file.
The files are drawn with a graphics resolution of 320 x 200. The Atari screen mode
restricts colours to 5, but these can be allocated from a base of 128 different colours.
White is always used for text and Black is always used for the background.
Assuming that origin is at the top left of the screen. The area used for images starts
at (24,0) and extends to (304,159). This leaves a miniscule space of screen of 4 lines
for text descriptions! On areas where the image is smaller than normal the text uses the
The image data for the first image starts at 0x297, and the images follow sequentially.
The image data seems closely related to the PC image data.
|0x00||0xfe||Size of image low byte|
|0x01||0x05||Size of image high byte|
|0x02||0x03||Minimum X co-ordinate (in blocks of 8 pixels) (MinX)|
|0x03||0x00||Minimum Y co-ordinate (MinY)|
|0x04||0x26||Maximum X co-ordinate (in blocks of 8 pixels) (MaxX)|
|0x05||0x9e||Maximum Y co-ordinate (MaxY)|
|0x06||0x0e||Colour for index 1|
|0x07||0x87||Colour for index 2|
|0x08||0x0e||Colour for index 3|
|0x09||0x00||Colour for index 0 (? - I've always seen it as 0x00)|
Note, the size doesn't always seem to lead perfectly to the next image, you may have to skip
0x00 bytes until you reach the header!
The Graphics Chunk
This is followed by the graphics chunk. The graphics are rended by a simple RLE encoding
if byte has bit 7 set
read byte1, byte2
repeat ((byte & 0x7F) + 1) times
plot byte1, byte2
repeat (byte + 1) times
read byte1, byte2
plot byte1, byte2
Note, due to the low amount of colours, the graphics data is set at 2 bits per pixel, with each
two bits representing a colour index from 0 - 4. All the x pixel values are plotted twice. For example
the value 0xa5 would be turn into eight pixels as:
To confuse issues, this version plots y first, rather than x. It always provides the next two
y values after the encoding. So the plotting order is:
get byte1, byte2
if y > MaxY
y = MinY
increase x (in blocks of 8 pixels)
Stop plotting when the x offset (in blocks of 8 pixels) gets greater than maxX (in blocks of 8 pixels).
Beyond this until the end of the graphics chunk the data is undefined.
Complex images are formed by overlaying other images over a basic image.
There are a couple of variations to the above format, both Voodoo Castle
and The Count are in a slightly more basic format - bit 7 of the counter byte
does nothing special - all counter bytes are treated as counters. Also, it matches the end of a column
on y >= ylen.
Image 55 on The Count is corrupt on the discs I have, but doesn't seem to be
used in the game.
The Sorcerer of Claymorgue Castle and The Hulk
fill up the second disc totally, meaning that the image for the inventory is kept on the first disc at
an index of 0x9890
Bytes 0xb390 to 0xb410 correspond to the content of sector 360 (0x0168) which contains the volume
table of contents of the disk (mostly a bitmap of used sectors). This is not part of the graphics data
and should be skipped. For the code below, this sector was edited out by hand with a hex editor.
The code is relatively simple to extract the images from the originals. Here is the C code I was using to test my extraction routines. It
uses the allegro library and will save the image as Output<image>.bmp. The CLI parameters
arledraw <disc2 image> <offset> <num images> <version flag>
The version flag should be y for Voodoo Castle
and The Count
You will also need a palette file. I stole this one from Atariwin
Note the C is not very good and was evolved and hacked during my tests!
The extracted images:
The Sorcerer of Claymorgue Castle
Buckaroo Banzai in the Fifth Dimension
The Thing and The Human Torch