Convert 8-bit PNG & GIF alpha channels to /SMasks in PDF #106
1 changed files with 76 additions and 48 deletions
124
src/img2pdf.py
124
src/img2pdf.py
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@ -85,9 +85,9 @@ FitMode = Enum("FitMode", "into fill exact shrink enlarge")
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PageOrientation = Enum("PageOrientation", "portrait landscape")
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Colorspace = Enum("Colorspace", "RGB L 1 CMYK CMYK;I RGBA P other")
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Colorspace = Enum("Colorspace", "RGB RGBA L LA 1 CMYK CMYK;I P other")
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ImageFormat = Enum("ImageFormat", "JPEG JPEG2000 CCITTGroup4 PNG TIFF MPO other")
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ImageFormat = Enum("ImageFormat", "JPEG JPEG2000 CCITTGroup4 PNG GIF TIFF MPO other")
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PageMode = Enum("PageMode", "none outlines thumbs")
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@ -760,7 +760,7 @@ class pdfdoc(object):
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artborder=None,
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iccp=None,
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):
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assert color != Colorspace.RGBA or (imgformat == ImageFormat.PNG and smaskdata is not None)
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assert (color != Colorspace.RGBA and color != Colorspace.LA) or (imgformat == ImageFormat.PNG and smaskdata is not None)
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if self.engine == Engine.pikepdf:
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PdfArray = pikepdf.Array
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@ -780,7 +780,7 @@ class pdfdoc(object):
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TrueObject = True if self.engine == Engine.pikepdf else PdfObject("true")
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FalseObject = False if self.engine == Engine.pikepdf else PdfObject("false")
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if color == Colorspace["1"] or color == Colorspace.L:
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if color == Colorspace["1"] or color == Colorspace.L or color == Colorspace.LA:
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colorspace = PdfName.DeviceGray
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elif color == Colorspace.RGB or color == Colorspace.RGBA:
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colorspace = PdfName.DeviceRGB
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@ -819,7 +819,7 @@ class pdfdoc(object):
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else:
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iccpdict = PdfDict(stream=convert_load(iccp))
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iccpdict[PdfName.Alternate] = colorspace
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if color == Colorspace["1"] or color == Colorspace.L:
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if color == Colorspace["1"] or color == Colorspace.L or color == Colorspace.LA:
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iccpdict[PdfName.N] = 1
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elif color == Colorspace.RGB or color == Colorspace.RGBA:
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iccpdict[PdfName.N] = 3
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@ -872,7 +872,7 @@ class pdfdoc(object):
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decodeparms[PdfName.Rows] = imgheightpx
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image[PdfName.DecodeParms] = [decodeparms]
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elif imgformat is ImageFormat.PNG:
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if color == Colorspace.RGBA:
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if smaskdata is not None:
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if self.engine == Engine.pikepdf:
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smask = self.writer.make_stream(smaskdata)
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else:
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@ -890,16 +890,16 @@ class pdfdoc(object):
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# /SMask requires PDF 1.4
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if self.output_version < "1.4":
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self.output_version = "1.4"
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decodeparms = PdfDict()
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decodeparms[PdfName.Predictor] = 15
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if color in [Colorspace.P, Colorspace["1"], Colorspace.L, Colorspace.LA]:
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decodeparms[PdfName.Colors] = 1
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else:
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decodeparms = PdfDict()
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decodeparms[PdfName.Predictor] = 15
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if color in [Colorspace.P, Colorspace["1"], Colorspace.L]:
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decodeparms[PdfName.Colors] = 1
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else:
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decodeparms[PdfName.Colors] = 3
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decodeparms[PdfName.Columns] = imgwidthpx
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decodeparms[PdfName.BitsPerComponent] = depth
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image[PdfName.DecodeParms] = decodeparms
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decodeparms[PdfName.Colors] = 3
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decodeparms[PdfName.Columns] = imgwidthpx
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decodeparms[PdfName.BitsPerComponent] = depth
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image[PdfName.DecodeParms] = decodeparms
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text = (
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"q\n%0.4f 0 0 %0.4f %0.4f %0.4f cm\n/Im0 Do\nQ"
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@ -1208,8 +1208,19 @@ def get_imgmetadata(
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ndpi = (int(round(ndpi[0])), int(round(ndpi[1])))
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ics = imgdata.mode
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if imgformat == ImageFormat.PNG and ics == "RGBA":
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logger.warning("Image contains an alpha channel which will be stored as a separate soft mask (/SMask) image in PDF.")
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# GIF and PNG files with transparency are supported
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if (
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(imgformat == ImageFormat.PNG or imgformat == ImageFormat.GIF)
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and (ics in ["RGBA", "LA"] or "transparency" in imgdata.info)
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):
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# Must check the IHDR chunk for the bit depth, because PIL would lossily
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# convert 16-bit RGBA/LA images to 8-bit.
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if imgformat == ImageFormat.PNG and rawdata != None:
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depth = rawdata[24]
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if depth > 8:
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logger.warning("Image with transparency and a bit depth of %d." % depth)
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logger.warning("This is unsupported due to PIL limitations.")
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raise AlphaChannelError("Refusing to work with multiple >8bit channels.")
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elif (ics in ["LA", "PA", "RGBA"] or "transparency" in imgdata.info):
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logger.warning("Image contains transparency which cannot be retained in PDF.")
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logger.warning("img2pdf will not perform a lossy operation.")
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@ -1523,7 +1534,7 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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img_page_count += 1
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cleanup()
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return result
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# We can directly embed the IDAT chunk of PNG images if the PNG is not
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# interlaced
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#
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@ -1531,21 +1542,12 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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# or not. Thus, we retrieve that info manually by looking at byte 13 in the
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# IHDR chunk. We know where to find that in the file because the IHDR chunk
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# must be the first chunk.
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if imgformat == ImageFormat.PNG:
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if imgformat == ImageFormat.PNG and rawdata[28] == 0:
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color, ndpi, imgwidthpx, imgheightpx, rotation, iccp = get_imgmetadata(
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imgdata, imgformat, default_dpi, colorspace, rawdata, rot
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)
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if color == Colorspace.RGBA or rawdata[28] == 0:
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if color == Colorspace.RGBA:
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r, g, b, a = imgdata.split()
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pngdata = zlib.compress(Image.merge("RGB", (r, g, b)).tobytes())
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smaskdata = zlib.compress(a.tobytes())
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palette = None
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else:
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pngdata, palette = parse_png(rawdata)
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smaskdata = None
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if color != Colorspace.RGBA and color != Colorspace.LA and "transparency" not in imgdata.info:
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pngidat, palette = parse_png(rawdata)
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# PIL does not provide the information about the original bits per
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# sample. Thus, we retrieve that info manually by looking at byte 9 in
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# the IHDR chunk. We know where to find that in the file because the
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@ -1560,8 +1562,8 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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color,
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ndpi,
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imgformat,
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pngdata,
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smaskdata,
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pngidat,
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None,
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imgwidthpx,
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imgheightpx,
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palette,
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@ -1703,7 +1705,9 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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color = Colorspace.L
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elif color in [
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Colorspace.RGB,
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Colorspace.RGBA,
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Colorspace.L,
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Colorspace.LA,
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Colorspace.CMYK,
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Colorspace["CMYK;I"],
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Colorspace.P,
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@ -1734,28 +1738,35 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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)
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)
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else:
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# cheapo version to retrieve a PNG encoding of the payload is to
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# just save it with PIL. In the future this could be replaced by
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# dedicated function applying the Paeth PNG filter to the raw pixel
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pngbuffer = BytesIO()
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newimg.save(pngbuffer, format="png")
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pngidat, palette = parse_png(pngbuffer.getvalue())
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# PIL does not provide the information about the original bits per
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# sample. Thus, we retrieve that info manually by looking at byte 9 in
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# the IHDR chunk. We know where to find that in the file because the
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# IHDR chunk must be the first chunk
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pngbuffer.seek(24)
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depth = ord(pngbuffer.read(1))
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if depth not in [1, 2, 4, 8, 16]:
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raise ValueError("invalid bit depth: %d" % depth)
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if color == Colorspace.RGBA or color == Colorspace.LA or "transparency" in newimg.info:
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if color == Colorspace.RGBA:
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newcolor = color
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r, g, b, a = newimg.split()
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newimg = Image.merge("RGB", (r, g, b))
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elif color == Colorspace.LA:
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newcolor = color
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l, a = newimg.split()
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newimg = l
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else:
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newcolor = Colorspace.RGBA
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r, g, b, a = newimg.convert(mode="RGBA").split()
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newimg = Image.merge("RGB", (r, g, b))
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smaskdata = zlib.compress(a.tobytes())
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logger.warning("Image contains an alpha channel which will be stored as a separate soft mask (/SMask) image in PDF.")
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else:
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newcolor = color
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smaskdata = None
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pngidat, palette, depth = to_png_data(newimg)
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logger.debug("read_images() encoded an image as PNG")
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result.append(
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(
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color,
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newcolor,
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ndpi,
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ImageFormat.PNG,
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pngidat,
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None,
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smaskdata,
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imgwidthpx,
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imgheightpx,
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palette,
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@ -1769,6 +1780,23 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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cleanup()
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return result
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def to_png_data(img):
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# cheapo version to retrieve a PNG encoding of the payload is to
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# just save it with PIL. In the future this could be replaced by
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# dedicated function applying the Paeth PNG filter to the raw pixel
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pngbuffer = BytesIO()
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img.save(pngbuffer, format="png")
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pngidat, palette = parse_png(pngbuffer.getvalue())
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# PIL does not provide the information about the original bits per
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# sample. Thus, we retrieve that info manually by looking at byte 9 in
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# the IHDR chunk. We know where to find that in the file because the
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# IHDR chunk must be the first chunk
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pngbuffer.seek(24)
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depth = ord(pngbuffer.read(1))
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if depth not in [1, 2, 4, 8, 16]:
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raise ValueError("invalid bit depth: %d" % depth)
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return pngidat, palette, depth
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# converts a length in pixels to a length in PDF units (1/72 of an inch)
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def px_to_pt(length, dpi):
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