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''' Takes care about pictures formats
References:
- JFIF: http://www.ecma-international.org/publications/techreports/E-TR-098.htm
- PNG: http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/PNG.html
- PNG: http://www.w3.org/TR/PNG-Chunks.html
'''
import parser
class JpegStripper(parser.GenericParser):
''' Represents a jpeg file.
Custom Huffman and Quantization tables
are stripped: they may leak
some info, and the quality loss is minor.
'''
def _should_remove(self, field):
''' Return True if the field is compromising
'''
field_list = frozenset([
'start_image', # start of the image
'app0', # JFIF data
'start_frame', # specify width, height, number of components
'start_scan', # specify which slice of data the top-to-bottom scan contains
'data', # actual data
'end_image']) # end of the image
if field.name in field_list:
return False
elif field.name.startswith('quantization['): # custom Quant. tables
return False
elif field.name.startswith('huffman['): # custom Huffman tables
return False
return True
class PngStripper(parser.GenericParser):
''' Represents a png file
'''
def _should_remove(self, field):
''' Return True if the field is compromising
'''
field_list = frozenset([
'id',
'header', # PNG header
'physical', # the intended pixel size or aspect ratio
'end']) # end of the image
if field.name in field_list:
return False
if field.name.startswith('data['): # data
return False
return True
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