Convert 8-bit PNG & GIF alpha channels to /SMasks in PDF #106
1 changed files with 84 additions and 39 deletions
123
src/img2pdf.py
123
src/img2pdf.py
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@ -742,6 +742,7 @@ class pdfdoc(object):
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imgheightpx,
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imgformat,
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imgdata,
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smaskdata,
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imgwidthpdf,
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imgheightpdf,
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imgxpdf,
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@ -759,6 +760,8 @@ 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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if self.engine == Engine.pikepdf:
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PdfArray = pikepdf.Array
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PdfDict = pikepdf.Dictionary
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@ -779,7 +782,7 @@ class pdfdoc(object):
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if color == Colorspace["1"] or color == Colorspace.L:
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colorspace = PdfName.DeviceGray
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elif color == Colorspace.RGB:
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elif color == Colorspace.RGB or color == Colorspace.RGBA:
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colorspace = PdfName.DeviceRGB
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elif color == Colorspace.CMYK or color == Colorspace["CMYK;I"]:
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colorspace = PdfName.DeviceCMYK
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@ -818,7 +821,7 @@ class pdfdoc(object):
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iccpdict[PdfName.Alternate] = colorspace
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if color == Colorspace["1"] or color == Colorspace.L:
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iccpdict[PdfName.N] = 1
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elif color == Colorspace.RGB:
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elif color == Colorspace.RGB or color == Colorspace.RGBA:
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iccpdict[PdfName.N] = 3
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elif color == Colorspace.CMYK or color == Colorspace["CMYK;I"]:
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iccpdict[PdfName.N] = 4
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@ -869,15 +872,34 @@ 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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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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if color == Colorspace.RGBA:
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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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smask = PdfDict(stream=convert_load(smaskdata))
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smask[PdfName.Type] = PdfName.XObject
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smask[PdfName.Subtype] = PdfName.Image
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smask[PdfName.Filter] = PdfName.FlateDecode
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smask[PdfName.Width] = imgwidthpx
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smask[PdfName.Height] = imgheightpx
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smask[PdfName.ColorSpace] = PdfName.DeviceGray
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smask[PdfName.BitsPerComponent] = depth
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image[PdfName.SMask] = smask
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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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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 = 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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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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@ -954,6 +976,8 @@ class pdfdoc(object):
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if self.engine == Engine.internal:
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self.writer.addobj(content)
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self.writer.addobj(image)
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if smask is not None:
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self.writer.addobj(smask)
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if iccp is not None:
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self.writer.addobj(iccpdict)
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@ -1183,8 +1207,10 @@ def get_imgmetadata(
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# Search online for the 72.009 dpi problem for more info.
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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 ics in ["LA", "PA", "RGBA"] or "transparency" in imgdata.info:
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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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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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logger.warning("You can remove the alpha channel using imagemagick:")
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@ -1427,6 +1453,7 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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ndpi,
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imgformat,
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rawdata,
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None,
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imgwidthpx,
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imgheightpx,
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[],
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@ -1483,6 +1510,7 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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ndpi,
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ImageFormat.JPEG,
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rawdata[offset : offset + mpent["Size"]],
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None,
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imgwidthpx,
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imgheightpx,
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[],
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@ -1495,7 +1523,7 @@ 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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@ -1503,35 +1531,46 @@ 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 and rawdata[28] == 0:
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if imgformat == ImageFormat.PNG:
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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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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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# IHDR chunk must be the first chunk
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depth = rawdata[24]
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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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logger.debug("read_images() embeds a PNG")
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cleanup()
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return [
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(
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color,
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ndpi,
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imgformat,
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pngidat,
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imgwidthpx,
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imgheightpx,
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palette,
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False,
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depth,
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rotation,
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iccp,
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)
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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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# 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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depth = rawdata[24]
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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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logger.debug("read_images() embeds a PNG")
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cleanup()
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return [
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(
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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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imgwidthpx,
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imgheightpx,
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palette,
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False,
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depth,
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rotation,
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iccp,
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)
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]
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# If our input is not JPEG or PNG, then we might have a format that
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# supports multiple frames (like TIFF or GIF), so we need a loop to
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@ -1615,6 +1654,7 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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ndpi,
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ImageFormat.CCITTGroup4,
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rawdata,
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None,
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imgwidthpx,
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imgheightpx,
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[],
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@ -1644,6 +1684,7 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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ndpi,
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ImageFormat.CCITTGroup4,
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ccittdata,
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None,
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imgwidthpx,
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imgheightpx,
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[],
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@ -1682,6 +1723,7 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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ndpi,
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imgformat,
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imggz,
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None,
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imgwidthpx,
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imgheightpx,
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[],
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@ -1713,6 +1755,7 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
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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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imgwidthpx,
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imgheightpx,
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palette,
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@ -2118,6 +2161,7 @@ def convert(*images, **kwargs):
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ndpi,
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imgformat,
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imgdata,
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smaskdata,
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imgwidthpx,
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imgheightpx,
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palette,
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@ -2171,6 +2215,7 @@ def convert(*images, **kwargs):
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imgheightpx,
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imgformat,
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imgdata,
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smaskdata,
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imgwidthpdf,
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imgheightpdf,
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imgxpdf,
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