josch/img2pdf
3
6
Fork 10
Code Issues 22 Pull requests 5 Projects Releases 3 Wiki Activity

read horizontal and vertical dpi from jpeg2000 files

Browse source
This commit is contained in:
Johannes 'josch' Schauer 2016-02-17 20:30:58 +01:00
parent ef9eac7326
commit e5b0ffee6c
1 changed files with 30 additions and 7 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

37
src/jp2.py
View file

@ -56,8 +56,29 @@ def parse_colr(data):
"got %d" % enumCS) "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): def parse_jp2h(data):
width, height, colorspace = None, None, None width, height, colorspace, hdpi, vdpi = None, None, None, None, None
noBytes = len(data) noBytes = len(data)
byteStart = 0 byteStart = 0
boxLengthValue = 1 # dummy value for while loop condition boxLengthValue = 1 # dummy value for while loop condition
@ -68,22 +89,23 @@ def parse_jp2h(data):
width, height = parse_ihdr(boxContents) width, height = parse_ihdr(boxContents)
elif boxType == b'colr': elif boxType == b'colr':
colorspace = parse_colr(boxContents) colorspace = parse_colr(boxContents)
elif boxType == b'res ':
hdpi, vdpi = parse_res(boxContents)
byteStart = byteEnd byteStart = byteEnd
return (width, height, colorspace) return (width, height, colorspace, hdpi, vdpi)
def parsejp2(data): def parsejp2(data):
noBytes = len(data) noBytes = len(data)
byteStart = 0 byteStart = 0
boxLengthValue = 1 # dummy value for while loop condition boxLengthValue = 1 # dummy value for while loop condition
width = None width, height, colorspace, hdpi, vdpi = None, None, None, None, None
height = None
colorspace = None
while byteStart < noBytes and boxLengthValue != 0: while byteStart < noBytes and boxLengthValue != 0:
boxLengthValue, boxType, byteEnd, boxContents = \ boxLengthValue, boxType, byteEnd, boxContents = \
getBox(data, byteStart, noBytes) getBox(data, byteStart, noBytes)
if boxType == b'jp2h': if boxType == b'jp2h':
width, height, colorspace = parse_jp2h(boxContents) width, height, colorspace, hdpi, vdpi = parse_jp2h(boxContents)
break
byteStart = byteEnd byteStart = byteEnd
if not width: if not width:
raise Exception("no width in jp2 header") raise Exception("no width in jp2 header")
@ -91,7 +113,8 @@ def parsejp2(data):
raise Exception("no height in jp2 header") raise Exception("no height in jp2 header")
if not colorspace: if not colorspace:
raise Exception("no colorspace in jp2 header") raise Exception("no colorspace in jp2 header")
return (width, height, colorspace) # retrieving the dpi is optional so we do not error out if not present
return (width, height, colorspace, hdpi, vdpi)
if __name__ == "__main__": if __name__ == "__main__":
import sys import sys