Atari_Ace's Blog - Bellcom disk 481, part 2, or flipping bits for fun

RSS Bot · August 3, 2018

In the last post we partially restored the first sector of Girl6.pic by splicing in some data into the RLE stream to represent 160 zero bytes. But we have a slightly different version of the picture, so in principle we can completely restore the picture from that and some ingenuity.

First, let's expand out the first column of GIRLJ.PIC (our more complete picture) and see what it looks like.

     0  00 00 00 00 ea ea ea ea-ea da fa ee e9 e9 e6 e9   ..........z.....    10  e5 e9 ea ea eb df ef eb-e7 d6 e9 d5 d5 d5 d5 d5   .......kgViU.UUU    20  d5 d5 d5 d5 e5 e9 e5 d5-d9 d5 fd f9 ff fe ff ff   UU.Ue..UYU......    30  ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................    40  ff ff ff 00 00 00 00 00-00 00 00 00 00 00 00 00   ................    50  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00   ................    60  00 00 00 ff ea e9 ea e9-e9 ea e9 ea ea e5 ea e6   .............e..    70  e9 ea ea da eb df ef eb-d6 d9 ea d5 d5 d5 d5 d5   .......k.Y..UUUU    80  d9 d5 d9 e9 e9 e5 d9 e5-d5 dd fd fe fb ff ff ff   YU.i.eYeU.......    90  ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................    a0  ff ff ff 00 00 00 00 00-00 00 00 00 00 00 00 00   ................    b0  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00   ................

Now we need to RLE encode these bytes into the file. It turns out the RLE for this is exactly the right size to fit into the 91 bytes we have available in the sector to contain these 160 bytes, strongly suggesting this is the right data restoration. So we end up with the following for sector 556.

And the picture even looks correct.



That was more work than I originally intended to expend on this disk, but it allowed me to learn at least a little bit about the MicroIllustrator compression format, so I think it was time well spent.

Attached thumbnail(s)