// HEADER
  4 - Header? (237,95,132,0)
  4 - Unknown (4)
  4 - Pixel Type (1=Grayscale, 2=RGB555)
  4 - File Data Length
  for most {
    48 - null
    }
  for some (only ones with LZO1X compression?) {
    4 - Unknown
    12 - null
    4 - Unknown
    4 - Unknown (1)
    4 - Unknown
    }
  
// DETAILS DIRECTORY
  4 - Number of Sprites
  
  // for each sprite
    4 - Offset (relative to the offset of this field)
    2 - X Position?
    2 - Y Position?
    2 - Sprite Width
    2 - Sprite Height
    2 - Unknown (32)
    2 - Compression Type (0=Raw RGB555, 1=RLE, 3=LZO1X+RGB555, 4=LZO1X+RLE, 5=Empty?)
    
// FILE DATA
  // for each file
    if (Compression Type == 0){
      if (PixelType == 1){
        X - Pixel Data (Grayscale)
        }
      else if (PixelType == 2){
        X - Pixel Data (RGB555)
        }
      }
    else if (Compression Type == 1){
      X - File Data (RLE encoding){
        // for each line {
          2 - Block Length
          X - Block {
            // repeat until we have a pixel for each of the sprite width {
              1 - Control Character (<128 = copy pixels raw, >128 = Repeat the next pixel X-128 times)
              X - Pixels (2-byte RGB555)
              }
            1 - null End Of Line character
        }
      }
    else if (Compression Type == 3){
      4 - Compressed Data Length
      4 - Decompressed Data Length
      X - File Data (Uncompress using LZO1X and then read RGB555 as per Compression Type 0){
      }
    else if (Compression Type == 4){
      4 - Compressed Data Length
      4 - Decompressed Data Length
      X - File Data (Uncompress using LZO1X and then apply RLE as per Compression Type 1){
      }
    else if (Compression Type == 5){
      1 - null
      }

An Image made up of lots of sprites.
Uses a basic type of RLE encoding. Also sometimes uses LZO1X compression on the RLE data.