Convert L15 raw to 8 bit pgm image

l15decode.py

#!/usr/bin/env python

"""l15decode.py: L15 image format decoder."""

import os, sys
from time import time
import array

NUMPY = False
try:
	import numpy
	NUMPY = True
except ImportError:
	pass

SIGNATURE_LEN = 16
# l15 chunk identifiers
CHUNK_ID_HDR = 0
CHUNK_ID_1 = 1
CHUNK_ID_2 = 2
CHUNK_ID_3 = 3
CHUNK_ID_4 = 4
CHUNK_ID_5 = 5
CHUNK_ID_6 = 6
CHUNK_ID_RAW = 7

def copy_bytes(fin, fout, length, block_size = 64 * 1024):
	out_bytes = 0
	while length > 0:
		to_read = min(length, block_size)
		length -= to_read
		b = fin.read(to_read)
		written = len(b)
		out_bytes += written
		fout.write(b)
	return out_bytes

def make_pbm(fname, width, height, colors):
	f = open(fname, "wb")
	f.write("P5\n")
	f.write("%d\n%d\n%d\n" % (width, height, colors))
	return f

def convert_line_16_to_8(aline, lcoef):
	lin = array.array("H", aline)
	lout = array.array("B")
	for p in lin:
		lout.append(int(p * lcoef))
#	lout.fromlist(map(lambda x: int(x * lrecip), lin))
	return lout

def convert_line_16_to_8_fast(aline, lcoef):
	lin = numpy.fromstring(aline, dtype=numpy.uint16)
	lout = (lin * lcoef).astype(numpy.uint8)
	return lout
	
#def convert_line_16(aline, 

def convert_img_chunk(fin, outname):
	ts = time()
	img_hdr = array.array("I")
	img_hdr.fromfile(fin, 6)
	img_lmax, img_unk2, img_chan, img_width, img_height, img_bits = tuple(img_hdr)
	print "Image: %dx%dx%d" % (img_width, img_height, img_bits)
	img_stride = img_width * (img_bits / 2)
	lcoef = 255.0 / 0x400
	cvt = convert_line_16_to_8_fast if NUMPY else convert_line_16_to_8
	with make_pbm(outname, img_width, img_height, 255) as pbm:
		#copy_bytes(fin, pbm, img_height * img_width * (img_bits / 8))
		for ln in range(0, img_height):
			in_bytes = fin.read(img_stride)
			out_bytes = cvt(in_bytes, lcoef)
			out_bytes.tofile(pbm)
			if not ln % 10: print ln, "\r",
	print time() - ts, "seconds."

def dump_chunk(fin, bytes, outfile):
	with open(outfile, "wb") as fout:
		copy_bytes(fin, fout, bytes)

def parse_l15(fname):
	with open(fname, "rb") as f:
		signature = f.read(SIGNATURE_LEN)
		# a little magic due the first chunk size being an offset from the file head
		chunk_ofs = -SIGNATURE_LEN

		while True:
			try:
				mark = f.tell()
				chunk_hdr = array.array("I")
				chunk_hdr.fromfile(f, 2)

				chunk_id, chunk_len = chunk_hdr[0], chunk_hdr[1]
				print "Chunk %08x : %08x" % (chunk_id, chunk_len)

				yield f, chunk_id, chunk_len

				seek_to, chunk_ofs = mark + chunk_len + chunk_ofs, 0
				f.seek(seek_to, os.SEEK_SET)
			except EOFError:
				break

def convert_l15(fname, outfile):
	"""Read L15 and process chunk by chunk writting results to the outfile"""
	for fin, chunk_id, chunk_len in parse_l15(fname):
		if chunk_id == CHUNK_ID_RAW:
			convert_img_chunk(fin, outfile + ".pbm")
		else:
			dump_chunk(fin, chunk_len, outfile + ".chunk." + str(chunk_id))

if __name__ == "__main__":
	# substitue your input file
	convert_l15("1520_1_270312160000_1.L15", "result")