@@ -1521,28 +1521,34 @@ def _unpack(self, im):
15211521alpha = None
15221522return rgb ,alpha
15231523
1524- def _writePng (self ,data ):
1524+ def _writePng (self ,img ):
15251525"""
1526- Write the image *data * into the pdf file using png
1526+ Write the image *img * into the pdf file using png
15271527 predictors with Flate compression.
15281528 """
15291529buffer = BytesIO ()
1530- if data .shape [- 1 ]== 1 :
1531- data = data .squeeze (axis = - 1 )
1532- Image .fromarray (data ).save (buffer ,format = "png" )
1530+ img .save (buffer ,format = "png" )
15331531buffer .seek (8 )
1532+ png_data = b''
1533+ bit_depth = palette = None
15341534while True :
15351535length ,type = struct .unpack (b'!L4s' ,buffer .read (8 ))
1536- if type == b' IDAT'
1536+ if type in [ b'IHDR' , b'PLTE' , b' IDAT'] :
15371537data = buffer .read (length )
15381538if len (data )!= length :
15391539raise RuntimeError ("truncated data" )
1540- self .currentstream .write (data )
1540+ if type == b'IHDR' :
1541+ bit_depth = int (data [8 ])
1542+ elif type == b'PLTE' :
1543+ palette = data
1544+ elif type == b'IDAT' :
1545+ png_data += data
15411546elif type == b'IEND' :
15421547break
15431548else :
15441549buffer .seek (length ,1 )
15451550buffer .seek (4 ,1 )# skip CRC
1551+ return png_data ,bit_depth ,palette
15461552
15471553def _writeImg (self ,data ,id ,smask = None ):
15481554"""
@@ -1551,17 +1557,40 @@ def _writeImg(self, data, id, smask=None):
15511557 (alpha channel) *smask*, which should be either None or a ``(height,
15521558 width, 1)`` array.
15531559 """
1554- height ,width ,colors = data .shape
1560+ height ,width ,color_channels = data .shape
15551561obj = {'Type' :Name ('XObject' ),
15561562'Subtype' :Name ('Image' ),
15571563'Width' :width ,
15581564'Height' :height ,
1559- 'ColorSpace' :Name ({1 :'DeviceGray' ,3 :'DeviceRGB' }[colors ]),
1565+ 'ColorSpace' :Name ({1 :'DeviceGray' ,
1566+ 3 :'DeviceRGB' }[color_channels ]),
15601567'BitsPerComponent' :8 }
15611568if smask :
15621569obj ['SMask' ]= smask
15631570if mpl .rcParams ['pdf.compression' ]:
1564- png = {'Predictor' :10 ,'Colors' :colors ,'Columns' :width }
1571+ if data .shape [- 1 ]== 1 :
1572+ data = data .squeeze (axis = - 1 )
1573+ img = Image .fromarray (data )
1574+ img_colors = img .getcolors (maxcolors = 256 )
1575+ if color_channels == 3 and img_colors is not None :
1576+ # Convert to indexed color if there are 256 colors or fewer
1577+ # This can significantly reduce the file size
1578+ num_colors = len (img_colors )
1579+ img = img .convert (mode = 'P' ,dither = Image .NONE ,
1580+ palette = Image .ADAPTIVE ,colors = num_colors )
1581+ png_data ,bit_depth ,palette = self ._writePng (img )
1582+ if bit_depth is None or palette is None :
1583+ raise RuntimeError ("invalid PNG header" )
1584+ palette = palette [:num_colors * 3 ]# Trim padding
1585+ palette = pdfRepr (palette )
1586+ obj ['ColorSpace' ]= Verbatim (b'[/Indexed /DeviceRGB '
1587+ + str (num_colors - 1 ).encode ()
1588+ + b' ' + palette + b']' )
1589+ obj ['BitsPerComponent' ]= bit_depth
1590+ color_channels = 1
1591+ else :
1592+ png_data ,_ ,_ = self ._writePng (img )
1593+ png = {'Predictor' :10 ,'Colors' :color_channels ,'Columns' :width }
15651594else :
15661595png = None
15671596self .beginStream (
@@ -1571,7 +1600,7 @@ def _writeImg(self, data, id, smask=None):
15711600png = png
15721601 )
15731602if png :
1574- self ._writePng ( data )
1603+ self .currentstream . write ( png_data )
15751604else :
15761605self .currentstream .write (data .tobytes ())
15771606self .endStream ()