Enable support for CMYK images

CMYK TIFFs and JPEGs both work. CMYK JPEG2000 images have not been
tested. Adobe Photoshop and some other software generate inverted CMYK
JPEGs. The image is assumed to be inverted if the "Adobe" (APP14) tag is
present. Images can be forced inverted with `-C "CMYK;I"`, and forced
not inverted with `-C CMYK`.

src/img2pdf.py

@@ -121,9 +121,11 @@ class pdfdoc(object):
 
     def addimage(self, color, width, height, imgformat, imgdata, pdf_x, pdf_y):
         if color == 'L':
-            color = "/DeviceGray"
+            colorspace = "/DeviceGray"
         elif color == 'RGB':
-            color = "/DeviceRGB"
+            colorspace = "/DeviceRGB"
+        elif color == 'CMYK' or color == 'CMYK;I':
+            colorspace = "/DeviceCMYK"
         else:
             error_out("unsupported color space: %s"%color)
             exit(1)
@@ -145,12 +147,16 @@ class pdfdoc(object):
             "/Filter": ofilter,
             "/Width": width,
             "/Height": height,
-            "/ColorSpace": color,
+            "/ColorSpace": colorspace,
             # hardcoded as PIL doesnt provide bits for non-jpeg formats
             "/BitsPerComponent": 8,
             "/Length": len(imgdata)
         }, imgdata)
 
+        if color == 'CMYK;I':
+            # Inverts all four channels
+            image.content['/Decode'] = [1.0, 0.0, 1.0, 0.0, 1.0, 0.0, 1.0, 0.0]
+
         text = ("q\n%f 0 0 %f 0 0 cm\n/Im0 Do\nQ"%(pdf_x, pdf_y)).encode('utf8')
 
         content = obj({
@@ -252,6 +258,16 @@ def convert(images, dpi, x, y, title=None, author=None, creator=None, producer=N
                     debug_out("input colorspace (forced) = %s"%(color), verbose)
                 else:
                     color = imgdata.mode
+                    if color == "CMYK" and imgformat == "JPEG":
+                        # Adobe inverts CMYK JPEGs for some reason, and others
+                        # have followed suit as well. Some software assumes the
+                        # JPEG is inverted if the Adobe tag (APP14), while other
+                        # software assumes all CMYK JPEGs are inverted. I don't
+                        # have enough experience with these to know which is
+                        # better for images currently in the wild, so I'm going
+                        # with the first approach for now.
+                        if "adobe" in imgdata.info:
+                            color = "CMYK;I"
                     debug_out("input colorspace = %s"%(color), verbose)
 
             debug_out("width x height = %d x %d"%(width,height), verbose)
@@ -270,7 +286,7 @@ def convert(images, dpi, x, y, title=None, author=None, creator=None, producer=N
                     debug_out("Converting colorspace 1 to L", verbose)
                     imgdata = imgdata.convert('L')
                     color = 'L'
-                elif color in ("RGB", "L"):
+                elif color in ("RGB", "L", "CMYK", "CMYK;I"):
                     debug_out("Colorspace is OK: %s"%color, verbose)
                 else:
                     debug_out("Converting colorspace %s to RGB"%color, verbose)
@@ -347,7 +363,7 @@ parser.add_argument(
     help='keywords for metadata')
 parser.add_argument(
     '-C', '--colorspace', metavar='colorspace', type=str,
-    help='force PIL colorspace (one of: RGB, L, 1)')
+    help='force PIL colorspace (one of: RGB, L, 1, CMYK, CMYK;I)')
 parser.add_argument(
     '-D', '--nodate', help='do not add timestamps', action="store_true")
 parser.add_argument(