diff --git a/src/img2pdf_test.py b/src/img2pdf_test.py
index 24b0bc5..2d9448d 100755
--- a/src/img2pdf_test.py
+++ b/src/img2pdf_test.py
@@ -284,62 +284,35 @@ def write_png(data, path, bitdepth, colortype, palette=None, iccp=None):
         f.write(struct.pack(">I", 0) + block + struct.pack(">I", zlib.crc32(block)))
 
 
-def compare_ghostscript(tmpdir, img, pdf, gsdevice="png16m", exact=True, icc=False):
-    if gsdevice in ["png16m", "pnggray"]:
-        ext = "png"
-    elif gsdevice in ["tiff24nc", "tiff32nc", "tiff48nc"]:
-        ext = "tiff"
-    else:
-        raise Exception("unknown gsdevice: " + gsdevice)
-    subprocess.check_call(
-        [
-            "gs",
-            "-dQUIET",
-            "-dNOPAUSE",
-            "-dBATCH",
-            "-sDEVICE=" + gsdevice,
-            "-r96",
-            "-sOutputFile=" + str(tmpdir / "gs-") + "%00d." + ext,
-            str(pdf),
-        ]
-    )
+def compare(im1, im2, exact, icc, cmyk):
     if exact:
-        if icc:
-            subprocess.check_call(
-                [
-                    "compare",
-                    "-metric",
-                    "AE",
-                    "(",
-                    "-profile",
-                    "/usr/share/color/icc/ghostscript/srgb.icc",
-                    "-depth",
-                    "8",
-                    str(img),
-                    ")",
-                    str(tmpdir / "gs-1.") + ext,
-                    "null:",
-                ]
-            )
+        if cmyk:
+            raise Exception("cmyk cannot be exact")
+        elif icc:
+            raise Exception("icc cannot be exact")
         else:
             subprocess.check_call(
                 [
                     "compare",
                     "-metric",
                     "AE",
-                    str(img),
-                    str(tmpdir / "gs-1.") + ext,
+                    im1,
+                    im2,
                     "null:",
                 ]
             )
     else:
+        iccargs = []
+        if icc:
+            iccargs = ["-profile", "/usr/share/color/icc/sRGB.icc"]
         psnr = subprocess.run(
-            [
-                "compare",
+            ["compare"]
+            + iccargs
+            + [
                 "-metric",
                 "PSNR",
-                str(img),
-                str(tmpdir / "gs-1.") + ext,
+                im1,
+                im2,
                 "null:",
             ],
             check=False,
@@ -349,6 +322,28 @@ def compare_ghostscript(tmpdir, img, pdf, gsdevice="png16m", exact=True, icc=Fal
         psnr = float(psnr.strip(b"0"))
         assert psnr != 0  # or otherwise we would use the exact variant
         assert psnr > 50
+
+
+def compare_ghostscript(tmpdir, img, pdf, gsdevice="png16m", exact=True, icc=False):
+    if gsdevice in ["png16m", "pnggray"]:
+        ext = "png"
+    elif gsdevice in ["tiff24nc", "tiff32nc", "tiff48nc"]:
+        ext = "tiff"
+    else:
+        raise Exception("unknown gsdevice: " + gsdevice)
+    subprocess.check_call(
+        [
+            "gs",
+            "-dQUIET",
+            "-dNOPAUSE",
+            "-dBATCH",
+            "-sDEVICE=" + gsdevice,
+            "-r96",
+            "-sOutputFile=" + str(tmpdir / "gs-") + "%00d." + ext,
+            str(pdf),
+        ]
+    )
+    compare(str(img), str(tmpdir / "gs-1.") + ext, exact, icc, False)
     (tmpdir / ("gs-1." + ext)).unlink()
 
 
@@ -356,56 +351,7 @@ def compare_poppler(tmpdir, img, pdf, exact=True, icc=False):
     subprocess.check_call(
         ["pdftocairo", "-r", "96", "-png", str(pdf), str(tmpdir / "poppler")]
     )
-    if exact:
-        if icc:
-            raise Exception("not exact with icc")
-        subprocess.check_call(
-            [
-                "compare",
-                "-metric",
-                "AE",
-                str(img),
-                str(tmpdir / "poppler-1.png"),
-                "null:",
-            ]
-        )
-    else:
-        if icc:
-            psnr = subprocess.run(
-                [
-                    "compare",
-                    "-metric",
-                    "PSNR",
-                    "(",
-                    "-profile",
-                    "/usr/share/color/icc/ghostscript/srgb.icc",
-                    "-depth",
-                    "8",
-                    str(img),
-                    ")",
-                    str(tmpdir / "poppler-1.png"),
-                    "null:",
-                ],
-                check=False,
-                stderr=subprocess.PIPE,
-            ).stderr
-        else:
-            psnr = subprocess.run(
-                [
-                    "compare",
-                    "-metric",
-                    "PSNR",
-                    str(img),
-                    str(tmpdir / "poppler-1.png"),
-                    "null:",
-                ],
-                check=False,
-                stderr=subprocess.PIPE,
-            ).stderr
-        assert psnr != b"0"
-        psnr = float(psnr.strip(b"0"))
-        assert psnr != 0  # or otherwise we would use the exact variant
-        assert psnr > 50
+    compare(str(img), str(tmpdir / "poppler-1.png"), exact, icc, False)
     (tmpdir / "poppler-1.png").unlink()
 
 
@@ -422,20 +368,7 @@ def compare_mupdf(tmpdir, img, pdf, exact=True, cmyk=False):
         subprocess.check_call(
             ["mutool", "draw", "-r", "96", "-png", "-o", str(out), str(pdf)]
         )
-    if exact:
-        if cmyk:
-            raise Exception("cmyk cannot be exact")
-        subprocess.check_call(["compare", "-metric", "AE", str(img), str(out), "null:"])
-    else:
-        psnr = subprocess.run(
-            ["compare", "-metric", "PSNR", str(img), str(out), "null:"],
-            check=False,
-            stderr=subprocess.PIPE,
-        ).stderr
-        assert psnr != b"0"
-        psnr = float(psnr.strip(b"0"))
-        assert psnr != 0  # or otherwise we would use the exact variant
-        assert psnr > 50
+    compare(str(img), str(out), exact, False, cmyk)
     out.unlink()