#!/usr/bin/env python
#
# Copyright (C) 2013 Johannes Schauer Marin Rodrigues <j.schauer at email.de>
#
# this module is heavily based upon jpylyzer which is
# KB / National Library of the Netherlands, Open Planets Foundation
# and released under the same license conditions
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
import struct
def getBox(data, byteStart, noBytes):
boxLengthValue = struct.unpack(">I", data[byteStart : byteStart + 4])[0]
boxType = data[byteStart + 4 : byteStart + 8]
contentsStartOffset = 8
if boxLengthValue == 1:
boxLengthValue = struct.unpack(">Q", data[byteStart + 8 : byteStart + 16])[0]
contentsStartOffset = 16
if boxLengthValue == 0:
boxLengthValue = noBytes - byteStart
byteEnd = byteStart + boxLengthValue
boxContents = data[byteStart + contentsStartOffset : byteEnd]
return (boxLengthValue, boxType, byteEnd, boxContents)
def parse_ihdr(data):
height = struct.unpack(">I", data[0:4])[0]
width = struct.unpack(">I", data[4:8])[0]
return width, height
def parse_colr(data):
meth = struct.unpack(">B", data[0:1])[0]
if meth != 1:
raise Exception("only enumerated color method supported")
enumCS = struct.unpack(">I", data[3:])[0]
if enumCS == 16:
return "RGB"
elif enumCS == 17:
return "L"
else:
raise Exception(
"only sRGB and greyscale color space is supported, " "got %d" % enumCS
)
def parse_resc(data):
hnum, hden, vnum, vden, hexp, vexp = struct.unpack(">HHHHBB", data)
hdpi = ((hnum / hden) * (10 ** hexp) * 100) / 2.54
vdpi = ((vnum / vden) * (10 ** vexp) * 100) / 2.54
return hdpi, vdpi
def parse_res(data):
hdpi, vdpi = None, None
noBytes = len(data)
byteStart = 0
boxLengthValue = 1 # dummy value for while loop condition
while byteStart < noBytes and boxLengthValue != 0:
boxLengthValue, boxType, byteEnd, boxContents = getBox(data, byteStart, noBytes)
if boxType == b"resc":
hdpi, vdpi = parse_resc(boxContents)
break
return hdpi, vdpi
def parse_jp2h(data):
width, height, colorspace, hdpi, vdpi = None, None, None, None, None
noBytes = len(data)
byteStart = 0
boxLengthValue = 1 # dummy value for while loop condition
while byteStart < noBytes and boxLengthValue != 0:
boxLengthValue, boxType, byteEnd, boxContents = getBox(data, byteStart, noBytes)
if boxType == b"ihdr":
width, height = parse_ihdr(boxContents)
elif boxType == b"colr":
colorspace = parse_colr(boxContents)
elif boxType == b"res ":
hdpi, vdpi = parse_res(boxContents)
byteStart = byteEnd
return (width, height, colorspace, hdpi, vdpi)
def parsejp2(data):
noBytes = len(data)
byteStart = 0
boxLengthValue = 1 # dummy value for while loop condition
width, height, colorspace, hdpi, vdpi = None, None, None, None, None
while byteStart < noBytes and boxLengthValue != 0:
boxLengthValue, boxType, byteEnd, boxContents = getBox(data, byteStart, noBytes)
if boxType == b"jp2h":
width, height, colorspace, hdpi, vdpi = parse_jp2h(boxContents)
break
byteStart = byteEnd
if not width:
raise Exception("no width in jp2 header")
if not height:
raise Exception("no height in jp2 header")
if not colorspace:
raise Exception("no colorspace in jp2 header")
# retrieving the dpi is optional so we do not error out if not present
return (width, height, colorspace, hdpi, vdpi)
if __name__ == "__main__":
import sys
width, height, colorspace = parsejp2(open(sys.argv[1]).read())
sys.stdout.write("width = %d" % width)
sys.stdout.write("height = %d" % height)
sys.stdout.write("colorspace = %s" % colorspace)
