Also do not re-encode CCITT Group 4 encoded TIFF images

Add additional property of input images: inverted

closes: #47

README.md

@@ -29,16 +29,18 @@ input file format and image color space.
 | JPEG                 | any                            | direct        |
 | JPEG2000             | any                            | direct        |
 | PNG (non-interlaced) | any                            | direct        |
+| TIFF (CCITT Group 4) | monochrome                     | direct        |
 | any                  | any except CMYK and monochrome | PNG Paeth     |
 | any                  | monochrome                     | CCITT Group 4 |
 | any                  | CMYK                           | flate         |
 
-For JPEG, JPEG2000 and non-interlaced PNG input, img2pdf directly embeds the
+For JPEG, JPEG2000, non-interlaced PNG and TIFF images with CCITT Group 4
-image data into the PDF without re-encoding it. It thus treats the PDF format
+encoded data, img2pdf directly embeds the image data into the PDF without
-merely as a container format for the image data. In these cases, img2pdf only
+re-encoding it. It thus treats the PDF format merely as a container format for
-increases the filesize by the size of the PDF container (typically around 500
+the image data. In these cases, img2pdf only increases the filesize by the size
-to 700 bytes). Since data is only copied and not re-encoded, img2pdf is also
+of the PDF container (typically around 500 to 700 bytes). Since data is only
-typically faster than other solutions for these input formats.
+copied and not re-encoded, img2pdf is also typically faster than other
+solutions for these input formats.
 
 For all other input types, img2pdf first has to transform the pixel data to
 make it compatible with PDF. In most cases, the PNG Paeth filter is applied to

src/img2pdf.py

@@ -22,7 +22,7 @@ import sys
 import os
 import zlib
 import argparse
-from PIL import Image
+from PIL import Image, TiffImagePlugin
 from datetime import datetime
 from jp2 import parsejp2
 from enum import Enum
@@ -62,7 +62,7 @@ PageOrientation = Enum('PageOrientation', 'portrait landscape')
 
 Colorspace = Enum('Colorspace', 'RGB L 1 CMYK CMYK;I RGBA P other')
 
-ImageFormat = Enum('ImageFormat', 'JPEG JPEG2000 CCITTGroup4 PNG other')
+ImageFormat = Enum('ImageFormat', 'JPEG JPEG2000 CCITTGroup4 PNG TIFF other')
 
 PageMode = Enum('PageMode', 'none outlines thumbs')
 
@@ -374,7 +374,7 @@ class pdfdoc(object):
 
     def add_imagepage(self, color, imgwidthpx, imgheightpx, imgformat, imgdata,
                       imgwidthpdf, imgheightpdf, imgxpdf, imgypdf, pagewidth,
-                      pageheight, userunit=None, palette=None):
+                      pageheight, userunit=None, palette=None, inverted=False):
         if self.with_pdfrw:
             from pdfrw import PdfDict, PdfName, PdfObject, PdfString
             from pdfrw.py23_diffs import convert_load
@@ -440,8 +440,13 @@ class pdfdoc(object):
 
         if imgformat is ImageFormat.CCITTGroup4:
             decodeparms = PdfDict()
+            # The default for the K parameter is 0 which indicates Group 3 1-D
+            # encoding. We set it to -1 because we want Group 4 encoding.
             decodeparms[PdfName.K] = -1
-            decodeparms[PdfName.BlackIs1] = PdfObject('true')
+            if inverted:
+                decodeparms[PdfName.BlackIs1] = PdfObject('false')
+            else:
+                decodeparms[PdfName.BlackIs1] = PdfObject('true')
             decodeparms[PdfName.Columns] = imgwidthpx
             decodeparms[PdfName.Rows] = imgheightpx
             image[PdfName.DecodeParms] = [decodeparms]
@@ -685,11 +690,32 @@ def get_imgmetadata(imgdata, imgformat, default_dpi, colorspace, rawdata=None):
     return (color, ndpi, imgwidthpx, imgheightpx)
 
 
+def ccitt_payload_location_from_pil(img):
+    # If Pillow is passed an invalid compression argument it will ignore it;
+    # make sure the image actually got compressed.
+    if img.info['compression'] != 'group4':
+        raise ValueError("Image not compressed with CCITT Group 4 but with: %s" % img.info['compression'])
+
+    # Read the TIFF tags to find the offset(s) of the compressed data strips.
+    strip_offsets = img.tag_v2[TiffImagePlugin.STRIPOFFSETS]
+    strip_bytes = img.tag_v2[TiffImagePlugin.STRIPBYTECOUNTS]
+    rows_per_strip = img.tag_v2[TiffImagePlugin.ROWSPERSTRIP]
+
+    # PIL always seems to create a single strip even for very large TIFFs when
+    # it saves images, so assume we only have to read a single strip.
+    # A test ~10 GPixel image was still encoded as a single strip. Just to be
+    # safe check throw an error if there is more than one offset.
+    if len(strip_offsets) != 1 or len(strip_bytes) != 1:
+        raise NotImplementedError("Transcoding multiple strips not supported")
+
+    (offset, ), (length, ) = strip_offsets, strip_bytes
+
+    return offset, length
+
+
 def transcode_monochrome(imgdata):
     """Convert the open PIL.Image imgdata to compressed CCITT Group4 data"""
 
-    from PIL import TiffImagePlugin
-
     logging.debug("Converting monochrome to CCITT Group4")
 
     # Convert the image to Group 4 in memory. If libtiff is not installed and
@@ -707,27 +733,11 @@ def transcode_monochrome(imgdata):
     newimgio.seek(0)
     newimg = Image.open(newimgio)
 
-    # If Pillow is passed an invalid compression argument it will ignore it;
+    offset, length = ccitt_payload_location_from_pil(newimg)
-    # make sure the image actually got compressed.
-    if newimg.info['compression'] != 'group4':
-        raise ValueError("Image not compressed as expected")
 
-    # Read the TIFF tags to find the offset(s) of the compressed data strips.
+    newimgio.seek(offset)
-    strip_offsets = newimg.tag_v2[TiffImagePlugin.STRIPOFFSETS]
+    return newimgio.read(length)
-    strip_bytes = newimg.tag_v2[TiffImagePlugin.STRIPBYTECOUNTS]
-    rows_per_strip = newimg.tag_v2[TiffImagePlugin.ROWSPERSTRIP]
 
-    # PIL always seems to create a single strip even for very large TIFFs when
-    # it saves images, so assume we only have to read a single strip.
-    # A test ~10 GPixel image was still encoded as a single strip. Just to be
-    # safe check throw an error if there is more than one offset.
-    if len(strip_offsets) > 1:
-        raise NotImplementedError("Transcoding multiple strips not supported")
-
-    newimgio.seek(strip_offsets[0])
-    ccittdata = newimgio.read(strip_bytes[0])
-
-    return ccittdata
 
 def parse_png(rawdata):
     pngidat = b""
@@ -786,7 +796,7 @@ def read_images(rawdata, colorspace, first_frame_only=False):
         if color == Colorspace['RGBA']:
             raise JpegColorspaceError("jpeg can't have an alpha channel")
         im.close()
-        return [(color, ndpi, imgformat, rawdata, imgwidthpx, imgheightpx, [])]
+        return [(color, ndpi, imgformat, rawdata, imgwidthpx, imgheightpx, [], False)]
 
     # We can directly embed the IDAT chunk of PNG images if the PNG is not
     # interlaced
@@ -799,7 +809,27 @@ def read_images(rawdata, colorspace, first_frame_only=False):
         color, ndpi, imgwidthpx, imgheightpx = get_imgmetadata(
                 imgdata, imgformat, default_dpi, colorspace, rawdata)
         pngidat, palette = parse_png(rawdata)
-        return [(color, ndpi, imgformat, pngidat, imgwidthpx, imgheightpx, palette)]
+        im.close()
+        return [(color, ndpi, imgformat, pngidat, imgwidthpx, imgheightpx, palette, False)]
+
+    # We can directly copy the data out of a CCITT Group 4 encoded TIFF, if it
+    # only contains a single strip
+    if imgformat == ImageFormat.TIFF \
+        and imgdata.info['compression'] == "group4" \
+        and len(imgdata.tag_v2[TiffImagePlugin.STRIPOFFSETS]) == 1:
+        photo = imgdata.tag_v2[TiffImagePlugin.PHOTOMETRIC_INTERPRETATION]
+        inverted = False
+        if photo == 0:
+            inverted = True
+        elif photo != 1:
+            raise ValueError("unsupported photometric interpretation for group4 tiff: %d" % photo)
+        color, ndpi, imgwidthpx, imgheightpx = get_imgmetadata(
+                imgdata, imgformat, default_dpi, colorspace, rawdata)
+        offset, length = ccitt_payload_location_from_pil(imgdata)
+        im.seek(offset)
+        rawdata = im.read(length)
+        im.close()
+        return [(color, ndpi, ImageFormat.CCITTGroup4, rawdata, imgwidthpx, imgheightpx, [], inverted)]
 
     # Everything else has to be encoded
 
@@ -826,7 +856,7 @@ def read_images(rawdata, colorspace, first_frame_only=False):
                 ccittdata = transcode_monochrome(imgdata)
                 imgformat = ImageFormat.CCITTGroup4
                 result.append((color, ndpi, imgformat, ccittdata,
-                               imgwidthpx, imgheightpx, []))
+                               imgwidthpx, imgheightpx, [], False))
                 img_page_count += 1
                 continue
             except Exception as e:
@@ -845,7 +875,7 @@ def read_images(rawdata, colorspace, first_frame_only=False):
         if color in [Colorspace.CMYK, Colorspace["CMYK;I"]]:
             imggz = zlib.compress(newimg.tobytes())
             result.append((color, ndpi, imgformat, imggz, imgwidthpx,
-                           imgheightpx, []))
+                           imgheightpx, [], False))
         else:
             # cheapo version to retrieve a PNG encoding of the payload is to
             # just save it with PIL. In the future this could be replaced by
@@ -855,7 +885,7 @@ def read_images(rawdata, colorspace, first_frame_only=False):
             pngidat, palette = parse_png(pngbuffer.getvalue())
             imgformat = ImageFormat.PNG
             result.append((color, ndpi, imgformat, pngidat, imgwidthpx,
-                           imgheightpx, palette))
+                           imgheightpx, palette, False))
         img_page_count += 1
     # the python-pil version 2.3.0-1ubuntu3 in Ubuntu does not have the
     # close() method
@@ -1170,8 +1200,8 @@ def convert(*images, **kwargs):
                 # name so we now try treating it as raw image content
                 rawdata = img
 
-        for color, ndpi, imgformat, imgdata, imgwidthpx, imgheightpx, palette \
+        for color, ndpi, imgformat, imgdata, imgwidthpx, imgheightpx, \
-                in read_images(
+                palette, inverted in read_images(
                     rawdata, kwargs['colorspace'], kwargs['first_frame_only']):
             pagewidth, pageheight, imgwidthpdf, imgheightpdf = \
                 kwargs['layout_fun'](imgwidthpx, imgheightpx, ndpi)
@@ -1195,7 +1225,8 @@ def convert(*images, **kwargs):
             imgypdf = (pageheight - imgheightpdf)/2.0
             pdf.add_imagepage(color, imgwidthpx, imgheightpx, imgformat,
                               imgdata, imgwidthpdf, imgheightpdf, imgxpdf,
-                              imgypdf, pagewidth, pageheight, userunit, palette)
+                              imgypdf, pagewidth, pageheight, userunit,
+                              palette, inverted)
 
     if kwargs['outputstream']:
         pdf.tostream(kwargs['outputstream'])

src/tests/__init__.py

@@ -592,6 +592,9 @@ def test_suite():
                     if imgprops.DecodeParms:
                         if orig_img.format == 'PNG':
                             pngidat, palette = img2pdf.parse_png(orig_imgdata)
+                        elif orig_img.format == 'TIFF' and orig_img.info['compression'] == "group4":
+                            offset, length = img2pdf.ccitt_payload_location_from_pil(orig_img)
+                            pngidat = orig_imgdata[offset:offset+length]
                         else:
                             pngbuffer = BytesIO()
                             orig_img.save(pngbuffer, format="png")