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Break out TIFF G4 transcoding into its own function

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James R. Barlow 2016-07-21 14:42:48 -07:00 committed by Johannes 'josch' Schauer
parent 95f84f97bc
commit c27505486e
1 changed files with 52 additions and 23 deletions
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65
src/img2pdf.py
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@ -609,6 +609,45 @@ def get_imgmetadata(imgdata, imgformat, default_dpi, colorspace, rawdata=None):
return (color, ndpi, imgwidthpx, imgheightpx)
def transcode_monochrome(imgdata):
"""Convert the open PIL.Image imgdata to compressed CCITT Group4 data"""
from PIL import TiffImagePlugin
logging.debug("Converting monochrome to CCITT Group4")
# Convert the image to Group 4 in memory. If libtiff is not installed and
# Pillow is not compiled against it, .save() will raise an exception.
newimgio = BytesIO()
imgdata.save(newimgio, format='TIFF', compression='group4')
# Open new image in memory
newimgio.seek(0)
newimg = Image.open(newimgio)
# If Pillow is passed an invalid compression argument it will ignore it;
# make sure the image actually got compressed.
if newimg.info['compression'] != 'group4':
raise ValueError("Image not compressed as expected")
# Read the TIFF tags to find the offset(s) of the compressed data strips.
strip_offsets = newimg.tag_v2[TiffImagePlugin.STRIPOFFSETS]
strip_bytes = newimg.tag_v2[TiffImagePlugin.STRIPBYTECOUNTS]
rows_per_strip = newimg.tag_v2[TiffImagePlugin.ROWSPERSTRIP]
# PIL always seems to create a single strip even for very large TIFFs when
# it saves images, so assume we only have to read a single strip.
# A test ~10 GPixel image was still encoded as a single strip. Just to be
# safe check throw an error if there is more than one offset.
if len(strip_offsets) > 1:
raise NotImplementedError("Transcoding multiple strips not supported")
newimgio.seek(strip_offsets[0])
ccittdata = newimgio.read(strip_bytes[0])
return ccittdata
def read_images(rawdata, colorspace, first_frame_only=False):
im = BytesIO(rawdata)
im.seek(0)
@ -663,30 +702,20 @@ def read_images(rawdata, colorspace, first_frame_only=False):
color, ndpi, imgwidthpx, imgheightpx = get_imgmetadata(
imgdata, imgformat, default_dpi, colorspace)
newimg = None
if color == Colorspace['1']:
logging.debug("Converting monochrome to CCITT Group4")
# Convert the image to Group 4 in memory
newimgio = BytesIO()
imgdata.save(newimgio, format='TIFF', compression='group4')
# Open new image in memory
newimgio.seek(0)
newimg = Image.open(newimgio)
# Obtain tags
strip_offsets = newimg.tag_v2[273]
strip_bytes = newimg.tag_v2[279]
rows_per_strip = newimg.tag_v2[278]
newimgio.seek(strip_offsets[0])
ccittdata = newimgio.read(strip_bytes[0])
logging.debug("Extracted %i bytes from image" % len(ccittdata))
try:
ccittdata = transcode_monochrome(imgdata)
imgformat = ImageFormat.CCITTGroup4
result.append((color, ndpi, imgformat, ccittdata,
imgwidthpx, imgheightpx))
img_page_count += 1
continue
except Exception as e:
logging.debug(e)
logging.debug("Converting colorspace 1 to L")
newimg = imgdata.convert('L')
color = Colorspace.L
elif color in [Colorspace.RGB, Colorspace.L, Colorspace.CMYK,
Colorspace["CMYK;I"]]:
logging.debug("Colorspace is OK: %s", color)