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