A little script I wrote that converts Super Mario Maker .tnl course thumbnails to and from JPEG.

tnl_conv.py

# 6/16/16
# A little script I wrote that converts Super Mario Maker .tnl course
# thumbnails to and from JPEG. (Spoiler: TNL is an incredibly thin JPEG wrapper
# format.)

# Licensed under the MIT License:

# Copyright (c) 2016 RoadrunnerWMC

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

import binascii
import os.path
import struct
import sys


def tnl2Jpeg(tnlData):
    (jpegLen,) = struct.unpack_from('>I', tnlData, 4)
    return tnlData[8:8+jpegLen]


def jpeg2Tnl(jpegData):
    jpegLen = struct.pack('>I', len(jpegData))
    if len(jpegData) > 0xC7F8:
        raise ValueError('JPEG is too long! Maximum length is 0xC7F8 bytes.')

    padding = b'\0' * (0xC800 - len(jpegData) - 8)
    fileWithoutCRC = jpegLen + jpegData + padding

    crcInt = binascii.crc32(fileWithoutCRC) & 0xFFFFFFFF
    crc = bytes([crcInt >> 24, (crcInt >> 16) & 0xFF, (crcInt >> 8) & 0xFF, crcInt & 0xFF])

    return crc + fileWithoutCRC


def main(argv):
    if len(argv) not in (2, 3):
        print('Incorrect number of arguments.')
        print('Usage: tnl_conv filename [-j|-t]')
        print('    -j: Convert TNL to JPEG')
        print('    -t: Convert JPEG to TNL')
        print('    Default is -j.')
        return

    inpath = argv[1]

    with open(inpath, 'rb') as f:
        indata = f.read()

    conv = 'j'
    if len(argv) == 3 and argv[2] == '-t':
        conv = 't'

    if conv == 'j':
        outdata = tnl2Jpeg(indata)
        outpath = os.path.splitext(inpath)[0] + '.jpg'
    elif conv == 't':
        outdata = jpeg2Tnl(indata)
        outpath = os.path.splitext(inpath)[0] + '.tnl'

    with open(outpath, 'wb') as f:
        f.write(outdata)

if __name__ == '__main__': main(sys.argv)