Support imagemagick 7.1.0-48

- the output of -metric PSNR changed
 - CMYK output can now be exactly compared

closes: #148

src/img2pdf_test.py

@@ -75,6 +75,7 @@ for prog in ["convert", "compare", "identify"]:
         globals()[prog.upper()] = ["magick", prog]
 
 HAVE_IMAGEMAGICK_MODERN = True
+HAVE_EXACT_CMYK8 = True
 try:
     ver = subprocess.check_output(CONVERT + ["-version"], stderr=subprocess.STDOUT)
     m = re.fullmatch(
@@ -82,13 +83,18 @@ try:
     )
     if m is None:
         HAVE_IMAGEMAGICK_MODERN = False
+        HAVE_EXACT_CMYK8 = False
     else:
         if parse_version(m.group(1)) < parse_version("6.9.10-12"):
             HAVE_IMAGEMAGICK_MODERN = False
+        if parse_version(m.group(1)) < parse_version("7.1.0-48"):
+            HAVE_EXACT_CMYK8 = False
 except FileNotFoundError:
     HAVE_IMAGEMAGICK_MODERN = False
+    HAVE_EXACT_CMYK8 = False
 except subprocess.CalledProcessError:
     HAVE_IMAGEMAGICK_MODERN = False
+    HAVE_EXACT_CMYK8 = False
 
 if not HAVE_IMAGEMAGICK_MODERN:
     warnings.warn("imagemagick >= 6.9.10-12 not available, skipping certain checks...")
@@ -113,6 +119,12 @@ except subprocess.CalledProcessError:
 if not HAVE_JP2:
     warnings.warn("imagemagick has no jpeg 2000 support, skipping certain checks...")
 
+# the result of compare -metric PSNR is either just a floating point value or a
+# floating point value following by the same value multiplied by 0.01,
+# surrounded in parenthesis since ImagemMagick 7.1.0-48:
+# https://github.com/ImageMagick/ImageMagick/commit/751829cd4c911d7a42953a47c1f73068d9e7da2f
+psnr_re = re.compile(rb"((?:inf|(?:0|[1-9][0-9]*)(?:\.[0-9]+)?))(?: \([0-9.]+\))?")
+
 ###############################################################################
 #                               HELPER FUNCTIONS                              #
 ###############################################################################
@@ -310,8 +322,8 @@ def write_png(data, path, bitdepth, colortype, palette=None, iccp=None):
 
 def compare(im1, im2, exact, icc, cmyk):
     if exact:
-        if cmyk:
-            raise Exception("cmyk cannot be exact")
+        if cmyk and not HAVE_EXACT_CMYK8:
+            raise Exception("cmyk cannot be exact before ImageMagick 7.1.0-48")
         elif icc:
             raise Exception("icc cannot be exact")
         else:
@@ -345,7 +357,10 @@ def compare(im1, im2, exact, icc, cmyk):
             stderr=subprocess.PIPE,
         ).stderr
         assert psnr != b"0"
-        psnr = float(psnr.strip(b"0"))
+        assert psnr != b"0 (0)"
+        assert psnr_re.fullmatch(psnr) is not None, psnr
+        psnr = psnr_re.fullmatch(psnr).group(1)
+        psnr = float(psnr)
         assert psnr != 0  # or otherwise we would use the exact variant
         assert psnr > 50
 
@@ -501,7 +516,9 @@ def compare_pdfimages_png(tmpdir, img, pdf, exact=True, icc=False):
                 stderr=subprocess.PIPE,
             ).stderr
         assert psnr != b"0"
-        psnr = float(psnr.strip(b"0"))
+        assert psnr != b"0 (0)"
+        psnr = psnr_re.fullmatch(psnr).group(1)
+        psnr = float(psnr)
         assert psnr != 0  # or otherwise we would use the exact variant
         assert psnr > 50
     (tmpdir / "images-000.png").unlink()
@@ -5545,10 +5562,10 @@ def test_jpg_rot(tmp_path_factory, jpg_rot_img, jpg_rot_pdf):
 def test_jpg_cmyk(tmp_path_factory, jpg_cmyk_img, jpg_cmyk_pdf):
     tmpdir = tmp_path_factory.mktemp("jpg_cmyk")
     compare_ghostscript(
-        tmpdir, jpg_cmyk_img, jpg_cmyk_pdf, gsdevice="tiff32nc", exact=False
+        tmpdir, jpg_cmyk_img, jpg_cmyk_pdf, gsdevice="tiff32nc", exact=HAVE_EXACT_CMYK8
     )
     # not testing with poppler as it cannot write CMYK images
-    compare_mupdf(tmpdir, jpg_cmyk_img, jpg_cmyk_pdf, exact=False, cmyk=True)
+    compare_mupdf(tmpdir, jpg_cmyk_img, jpg_cmyk_pdf, exact=HAVE_EXACT_CMYK8, cmyk=True)
     compare_pdfimages_cmyk(tmpdir, jpg_cmyk_img, jpg_cmyk_pdf)
 
 
@@ -5902,10 +5919,16 @@ def test_tiff_float(tmp_path_factory, tiff_float_img, engine):
 def test_tiff_cmyk8(tmp_path_factory, tiff_cmyk8_img, tiff_cmyk8_pdf):
     tmpdir = tmp_path_factory.mktemp("tiff_cmyk8")
     compare_ghostscript(
-        tmpdir, tiff_cmyk8_img, tiff_cmyk8_pdf, gsdevice="tiff32nc", exact=False
+        tmpdir,
+        tiff_cmyk8_img,
+        tiff_cmyk8_pdf,
+        gsdevice="tiff32nc",
+        exact=HAVE_EXACT_CMYK8,
     )
     # not testing with poppler as it cannot write CMYK images
-    compare_mupdf(tmpdir, tiff_cmyk8_img, tiff_cmyk8_pdf, exact=False, cmyk=True)
+    compare_mupdf(
+        tmpdir, tiff_cmyk8_img, tiff_cmyk8_pdf, exact=HAVE_EXACT_CMYK8, cmyk=True
+    )
     compare_pdfimages_tiff(tmpdir, tiff_cmyk8_img, tiff_cmyk8_pdf)