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Attempt to read dpi information from JPEG2000's resc header box

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This commit is contained in:
Roger Baumgartner 2021-06-30 05:53:11 -07:00
parent 7f275c1bfc
commit 5f4653d0b4
2 changed files with 36 additions and 9 deletions
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5
Tests/test_file_jpeg2k.py
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@ -151,6 +151,11 @@ def test_reduce():
assert im.size == (40, 30)
def test_load_dpi():
with Image.open("Tests/images/test-card-lossless.jp2") as im:
assert im.info["dpi"] == (71.9836, 71.9836)
def test_layers_type(tmp_path):
outfile = str(tmp_path / "temp_layers.jp2")
for quality_layers in [[100, 50, 10], (100, 50, 10), None]:

40
src/PIL/Jpeg2KImagePlugin.py
View File

@ -6,6 +6,7 @@
#
# History:
# 2014-03-12 ajh Created
# 2021-06-30 rogermb Extract dpi information from the 'resc' header box
#
# Copyright (c) 2014 Coriolis Systems Limited
# Copyright (c) 2014 Alastair Houghton
@ -126,9 +127,21 @@ def _parse_codestream(fp):
return (size, mode)
def _res_to_dpi(num, denom, exp):
"""Convert JPEG2000's (numerator, denominator, exponent-base-10) resolution,
calculated as (num / denom) * 10^exp and stored in dots per meter,
to floating-point dots per inch."""
if num == 0 or denom == 0:
raise SyntaxError(
f"Invalid JP2 resolution information: ({num} / {denom}) * 10^{exp}"
)
return (254 * num * (10 ** exp)) / (10000 * denom)
def _parse_jp2_header(fp):
"""Parse the JP2 header box to extract size, component count and
color space information, returning a (size, mode, mimetype) tuple."""
"""Parse the JP2 header box to extract size, component count,
color space information, and optionally DPI information,
returning a (size, mode, mimetype, dpi) tuple."""
# Find the JP2 header box
reader = BoxReader(fp)
@ -151,6 +164,8 @@ def _parse_jp2_header(fp):
mode = None
bpc = None
nc = None
dpi = None # 2-tuple of DPI info, or None
unkc = 0 # Colorspace information unknown
while header.has_next_box():
tbox = header.next_box_type()
@ -169,10 +184,9 @@ def _parse_jp2_header(fp):
mode = "RGB"
elif nc == 4:
mode = "RGBA"
break
elif tbox == b"colr":
meth, prec, approx = header.read_fields(">BBB")
if meth == 1:
if meth == 1 and unkc == 0:
cs = header.read_fields(">I")[0]
if cs == 16: # sRGB
if nc == 1 and (bpc & 0x7F) > 8:
@ -183,7 +197,6 @@ def _parse_jp2_header(fp):
mode = "RGB"
elif nc == 4:
mode = "RGBA"
break
elif cs == 17: # grayscale
if nc == 1 and (bpc & 0x7F) > 8:
mode = "I;16"
@ -191,18 +204,25 @@ def _parse_jp2_header(fp):
mode = "L"
elif nc == 2:
mode = "LA"
break
elif cs == 18: # sYCC
if nc == 3:
mode = "RGB"
elif nc == 4:
mode = "RGBA"
break
elif tbox == b"res ":
res = header.read_boxes()
while res.has_next_box():
tres = res.next_box_type()
if tres == b"resc":
vrcn, vrcd, hrcn, hrcd, vrce, hrce = res.read_fields(">HHHHBB")
hres = _res_to_dpi(hrcn, hrcd, hrce)
vres = _res_to_dpi(vrcn, vrcd, vrce)
dpi = (hres, vres)
if size is None or mode is None:
raise SyntaxError("Malformed JP2 header")
return (size, mode, mimetype)
return (size, mode, mimetype, dpi)
##
@ -224,7 +244,9 @@ class Jpeg2KImageFile(ImageFile.ImageFile):
if sig == b"\x00\x00\x00\x0cjP \x0d\x0a\x87\x0a":
self.codec = "jp2"
header = _parse_jp2_header(self.fp)
self._size, self.mode, self.custom_mimetype = header
self._size, self.mode, self.custom_mimetype, dpi = header
if dpi is not None:
self.info["dpi"] = dpi
else:
raise SyntaxError("not a JPEG 2000 file")