Fix graphics format
The fix layer uses 8x8 pixels tiles, coded in a 4BPP linear format with mixed columns. Color indexes are coded by pairs and by columns from top to bottom. Note that the pixel positions are swapped in each byte (L/U) and that the first column is column A.
One tile is 8 * 8 pixels * 4 bits per pixel = 256 bits = 32 bytes.
Bit # ...543210 ...nHCLLL n: Tile number (multiple bits) H: Half, 0 = first (right), 1 = second (left) C: Column in half, 0 = left, 1 = right L: Line # (0~7)
2H1 is "C".