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Merge pull request #283 from manuelzs/support_for_png_average_and_paeth_filter 

Add support for PNG filters average and paeth
This commit is contained in:
Matthew Stamy 2016-08-15 13:51:51 -05:00 committed by GitHub
parent 036789a466 60abb83056
commit 6f284def98
2 changed files with 29 additions and 1 deletions
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16
PyPDF2/filters.py
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@ -34,7 +34,9 @@ Implementation of stream filters for PDF.
__author__ = "Mathieu Fenniak"
__author_email__ = "biziqe@mathieu.fenniak.net"
from .utils import PdfReadError, ord_, chr_
import math
from .utils import PdfReadError, ord_, chr_, paethPredictor
from sys import version_info
if version_info < ( 3, 0 ):
from cStringIO import StringIO
@ -137,6 +139,18 @@ class FlateDecode(object):
elif filterByte == 2:
for i in range(1, rowlength):
rowdata[i] = (rowdata[i] + prev_rowdata[i]) % 256
elif filterByte == 3:
for i in range(1, rowlength):
left = rowdata[i-1] if i > 1 else 0
floor = math.floor(left + prev_rowdata[i])/2
rowdata[i] = (rowdata[i] + int(floor)) % 256
elif filterByte == 4:
for i in range(1, rowlength):
left = rowdata[i - 1] if i > 1 else 0
up = prev_rowdata[i]
up_left = prev_rowdata[i - 1] if i > 1 else 0
paeth = paethPredictor(left, up, up_left)
rowdata[i] = (rowdata[i] + paeth) % 256
else:
# unsupported PNG filter
raise PdfReadError("Unsupported PNG filter %r" % filterByte)

14
PyPDF2/utils.py
View File

@ -293,3 +293,17 @@ def hexStr(num):
WHITESPACES = [b_(x) for x in [' ', '\n', '\r', '\t', '\x00']]
def paethPredictor(left, up, up_left):
p = left + up - up_left
dist_left = abs(p - left)
dist_up = abs(p - up)
dist_up_left = abs(p - up_left)
if dist_left <= dist_up and dist_left <= dist_up_left:
return left
elif dist_up <= dist_up_left:
return up
else:
return up_left