PICO-8 : Fantasy console

[Duke "Tape" Eiyeron]

I think each byte of the cart is spread on the last 2 bits of every channel:

take for instance, the keyword "local"

Code Select Expand

hex: 6c 6f 63 61 6c
binary: 0110 1100 0110 1111 0110 0011 0110 0001 0110 1100

now for a gray pixel on the png:

Code Select Expand

hex: 66 66 66 FF
binary: 0110 0110 0110 0110 0110 0110 1111 1111

now for each pixel, spread a char on the end of each channel:

Code Select Expand

binary:
0110 0101 0110 0110 0110 0111 1111 1100
0110 0101 0110 0110 0110 0111 1111 1111
0110 0101 0110 0110 0110 0100 1111 1111
0110 0101 0110 0110 0110 0100 1111 1101
0110 0101 0110 0110 0110 0111 1111 1100
hex:
65 66 67 FC
65 66 67 FF
65 66 64 FF
65 66 64 FD
65 66 67 FC

the color change is so subtle you can't even see it, but the data is still there
with a picture of 160*205, you have 32800 pixels, that makes 32K of data for a cart

Or you can just ask Lexaloffle. That's a classic way to store data in picture : changing the less signifiant bits.

[Snektron]

What if there's a secret message hidden in the original Walrii?

[Yuki]

I just wrote a little script to test this algorithm up, it indeed seems to work. I can see about 32K of memory with some Lua code in it.

[Dream of Omnimaga]

oh my god
I tried getting the code from a cart png with a text editor

I though it would just be some extensive metadata in the picture
I was wrong

the whole thing is encoded into the pixels themselves

Seems like something I wanted to do on-calc a while back.

What surprises me though is how someone uploaded a cart a while ago, yet I couldn't see any different color difference between pixels of the same hue.

[Duke "Tape" Eiyeron]

Hre's the base ram laout, found directly from the readme

Code Select Expand

0x0    gfx
0x1000 gfx2/map2 (shared)
0x2000 map
0x3000 gfx_props
0x3100 song
0x3200 sfx
0x4300 user-defined
0x5f00 draw state [,cart data] (1024 bytes incl. unused)
0x6000 screen (8k)


[Yuki]

What surprises me though is how someone uploaded a cart a while ago, yet I couldn't see any different color difference between pixels of the same hue.

The data is encoded in the 2 least signifiant bits of each channel, and a difference of 4 out of 255 in each color is pretty much imperceptible. Myself I was fooled, it's kind of incredible when you think about it.

[Dream of Omnimaga]

Yeah I didn't see the color difference myself, which is why I was wondering lol when Ivoah posted that 3D cart. I was asking myself: "Where is the code? O.o" It's a good idea I think, providing that people use common sense and don't start distributing cartridges in JPEG format.

[Siapran]

Yeah I didn't see the color difference myself, which is why I was wondering lol when Ivoah posted that 3D cart. I was asking myself: "Where is the code? O.o" It's a good idea I think, providing that people use common sense and don't start distributing cartridges in JPEG format.

if you're looking for the differences, check the 10~ rows of pixels under the green cube, that is the zone mapped to the code

(use GIMP or something)

[Dream of Omnimaga]

I actually maxed out the image gamma three times and I see it now

[CKH4]

That is very interesting, what's the blue line through the cube for?

[Snektron]

OH that's cool, really easy to see now

[Yuki]

[spoiler=Some random code]

Code Select Expand

<?php$im = new Imagick($argv[1]);$it = $im->getPixelIterator();foreach($it as $row => $pixels) {  foreach ($pixels as $column => $pixel) {    $c = $pixel->getColor();    $cn = $pixel->getColor(true);    $mem[] = ((floor($cn['a']*255)&3)<<6)|(($c['r']&3)<<4)|(($c['g']&3)<<2)|(($c['b'])&3);  }  $it->syncIterator();}for($i=0x4300;$mem[$i]!=0&&$i<count($mem);$i++){  echo chr($mem[$i]);}?>

[/spoiler]

I said absolutely nothing. >.>

So yeah, it's pretty much what Siapran said, but the alpha channel's 2 least signifiant bits are the characters' 2 most signifiant bytes, that is, it goes first. The memory map should be pretty much what the doc said about it, and Lua code starts at 0x4300 and probably goes until 0x7F00. Finding a library that doesn't convert the 8-bit alpha channel value to 7-bit (GD) or 1-bit (non-normalized Imagick) was kinda tedious, though.

[Strontium]

I lost my Lexaloffle acc. so I can't use PICO-8 anymore

[Dream of Omnimaga]

@Juju does that script return the actual code? I don't know PHP that much.

@Strontium that sucks . Did you get hacked or did you just forget your password? You should maybe contact the author about the issue in case he can restore your access.

[Snektron]

Maybe there are still some codes left, strontium. Atleast i hope so.

Also would it be possible to have more than 16k lua code by encoding it into the sprites, map, sound and music areas and just copying it somewhere else on runtime?
Guess not since the lua ram is not accessible :/