Hello Luisoft,
Thanks. I am confident that I can make it to 30.
I'm on 26 now. If I don't make the levels too large
it should work.
Propably you are referring to my 2010 entry Maze4K that used
a spritesheet. I'm honored that you want to take a look.
You have to do a little digging in the directory where
I host the game:
http://mazeland.net/maze4kIf you browse to
http://mazeland.net/maze4k/getcolor.javayou will get the source code for the converter tool.
You use it : java getcolor a.gif
My spritesheet:

It will create a file called a.gif.txt with some String code.
You copy-paste this code into your own project where you
decode it.
The a.java file contains the code for the game in which
you will find the technique to create a spritesheet from
this data.
Using strings you can use the compression qualities of
the kzip/7zip tools to make it really small. Riven's tool
is awesome with these strings.
This year I tried to do something clever like: if you see
9 times A write 9A instead of AAAAAAAAA.
It turns out that you can't beat the compression techniques
that are already provided in kZip. At least not without writing
much more decompression code which takes a lot of extra
bytes.
Funny thing is that some characters compress better than
others. You have to do a little experimentation with your
particular spritesheet. In my case I replaced # with a space
to get the best compression.
Good luck.
Best regards from
M.E.