PTX to BMP (development version)

import struct
import os
from functools import partial
#0x2: Size of file (4 bytes)
#0x6: Unused (4 bytes, all zero)
#0xA: Offset to bitmap data (4 bytes)
#0xE: DIB header bytes (always 40, 4 bytes)
#0x12: Bitmap width (4 bytes)
#0x16: Bitmap height (4 bytes)
#0x1A: Color planes used (2 bytes)
#0x1C: Bits per pixel (2 bytes)
#0x1E: Always zero (4 bytes)
#0x22: Size of raw bitmap data (4 bytes)
#0x26: Print resolution horizontal (4 bytes)
#0x2A: Print resolution vertical (4 bytes)
#0x2E: Colors in pallette
#0x32: Important colors (always zero, 4 bytes)

filename = 'logo.ptx'
with open(filename,'rb') as f:
    f.seek(4)
    unknown_1 = ord(f.read(1))                          #0x04
    unknown_2 = ord(f.read(1))                          #0x05
    width = struct.unpack('<H', f.read(2))[0]           #0x06
    actual_width = struct.unpack('<H', f.read(2))[0]    #0x08
    height = struct.unpack('<H', f.read(2))[0]          #0x0A
    #Bits flag: 4 for 4bpp, 5 for 8bpp
    bits_flag = ord(f.read(1))                          #0x0C
    #Unknown 3 and 4 are the same for every file
    unknown_3 = ord(f.read(1))                          #0x0D
    unknown_4 = ord(f.read(1))                          #0x0E
    #Colors flag: 0x2 for 16 colors, 0x4 for 32 colors,
    #0x8 for 64 colors, 0x10 for 128 colors, 0x20 for 256 colors
    colors_flag = ord(f.read(1))                        #0x0F
    colors = struct.unpack('<I', f.read(4))[0]          #0x10
    unknown_5 = ord(f.read(1))                          #0x14
    unknown_6 = ord(f.read(1))                          #0x15
    unknown_7 = struct.unpack('<H', f.read(2))[0]       #0x16
    color_table_addr = struct.unpack('<I', f.read(4))[0]#0x18
    bitmap_addr = struct.unpack('<I', f.read(4))[0]     #0x1C
    color_table = f.read(colors * 4)                    #32 bits per color
    bitmap = f.read()

if bits_flag == 4:
    BITS_PER_PIXEL = 4
elif bits_flag == 5:
    BITS_PER_PIXEL = 8
else:
    print('Unknown number of bits per pixel.')
    quit()
BMP_WIDTH = width
BMP_HEIGHT = len(bitmap) // width * 8 // BITS_PER_PIXEL
PALLETTE_COLORS = colors
write_int = partial(struct.pack, '<I')
write_hint = partial(struct.pack, '<H')
with open(os.path.splitext(filename)[0] + '.bmp','wb') as f:
    f.write(b'BM')                  #0x0 Signature
    f.write(write_int(0x36 + colors * 4 + len(bitmap))) #0x2 Size of file
    f.write(b'\x00'*4)              #0x6 Unused
    f.write(write_int(0x36 + 4 * colors))   #0xA Offset to bitmap data (4 bytes)
    f.write(write_int(40))          #0xE Size of DIB header
    f.write(write_int(BMP_WIDTH))   #0x12
    f.write(write_int(BMP_HEIGHT))  #0x16
    f.write(write_hint(1))          #0x1A Numer of color planes
    f.write(write_hint(BITS_PER_PIXEL))     #0x1C
    f.write(b'\x00'*4)              #0x1E Always zero (no compression used)
    f.write(write_int(len(bitmap))) #0x22 Size of bitmap data (minus header)
    f.write(write_int(0xB13)*2)     #0x26 72 DPI - Vert. + Horz. resolution
    f.write(write_int(PALLETTE_COLORS))     #0x2E
    f.write(b'\x00'*4)              #0x32 Important colors
    #End of header, start of color table
    f.write(color_table)
    #Bitmap data
    f.write(bitmap)