Add ImageShow support for GraphicsMagick

Tests/helper.py

@@ -257,8 +257,23 @@ def netpbm_available():
     return bool(shutil.which("ppmquant") and shutil.which("ppmtogif"))
 
 
-def imagemagick_available():
-    return bool(IMCONVERT and shutil.which(IMCONVERT))
+def magick_command():
+    if sys.platform == "win32":
+        magickhome = os.environ.get("MAGICK_HOME", "")
+        if magickhome:
+            imagemagick = [os.path.join(magickhome, "convert.exe")]
+            graphicsmagick = [os.path.join(magickhome, "gm.exe"), "convert"]
+        else:
+            imagemagick = None
+            graphicsmagick = None
+    else:
+        imagemagick = ["convert"]
+        graphicsmagick = ["gm", "convert"]
+
+    if imagemagick and shutil.which(imagemagick[0]):
+        return imagemagick
+    elif graphicsmagick and shutil.which(graphicsmagick[0]):
+        return graphicsmagick
 
 
 def on_appveyor():
@@ -296,14 +311,6 @@ def is_mingw():
     return sysconfig.get_platform() == "mingw"
 
 
-if sys.platform == "win32":
-    IMCONVERT = os.environ.get("MAGICK_HOME", "")
-    if IMCONVERT:
-        IMCONVERT = os.path.join(IMCONVERT, "convert.exe")
-else:
-    IMCONVERT = "convert"
-
-
 class cached_property:
     def __init__(self, func):
         self.func = func

Tests/test_file_palm.py

@@ -5,9 +5,7 @@
 
 from PIL import Image
 
-from .helper import IMCONVERT, assert_image_equal, hopper, imagemagick_available
-
-_roundtrip = imagemagick_available()
+from .helper import assert_image_equal, hopper, magick_command
 
 
 def helper_save_as_palm(tmp_path, mode):
@@ -23,28 +21,26 @@ def helper_save_as_palm(tmp_path, mode):
     assert os.path.getsize(outfile) > 0
 
 
-def open_with_imagemagick(tmp_path, f):
-    if not imagemagick_available():
-        raise OSError()
-
+def open_with_magick(magick, tmp_path, f):
     outfile = str(tmp_path / "temp.png")
     rc = subprocess.call(
-        [IMCONVERT, f, outfile], stdout=subprocess.DEVNULL, stderr=subprocess.STDOUT
+        magick + [f, outfile], stdout=subprocess.DEVNULL, stderr=subprocess.STDOUT
     )
     if rc:
         raise OSError
     return Image.open(outfile)
 
 
 def roundtrip(tmp_path, mode):
-    if not _roundtrip:
+    magick = magick_command()
+    if not magick:
         return
 
     im = hopper(mode)
     outfile = str(tmp_path / "temp.palm")
 
     im.save(outfile)
-    converted = open_with_imagemagick(tmp_path, outfile)
+    converted = open_with_magick(magick, tmp_path, outfile)
     assert_image_equal(converted, im)
 
 

docs/reference/ImageShow.rst

@@ -18,6 +18,7 @@ All default viewers convert the image to be shown to PNG format.
     The following viewers may be registered on Unix-based systems, if the given command is found:
 
     .. autoclass:: PIL.ImageShow.DisplayViewer
+    .. autoclass:: PIL.ImageShow.GmDisplayViewer
     .. autoclass:: PIL.ImageShow.EogViewer
     .. autoclass:: PIL.ImageShow.XVViewer
 

docs/releasenotes/8.2.0.rst

@@ -65,6 +65,18 @@ instances, so it will only be used by ``im.show()`` or :py:func:`.ImageShow.show
 if none of the other viewers are available. This means that the behaviour of
 :py:class:`PIL.ImageShow` will stay the same for most Pillow users.
 
+ImageShow.GmDisplayViewer
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If GraphicsMagick is present, this new :py:class:`PIL.ImageShow.Viewer` subclass will
+be registered. It uses GraphicsMagick_, an ImageMagick_ fork, to display images.
+
+The GraphicsMagick based viewer has a lower priority than its ImageMagick
+counterpart.  Thus, if both ImageMagick and GraphicsMagick are installed,
+``im.show()`` and :py:func:`.ImageShow.show()` prefer the viewer based on
+ImageMagick, i.e the behaviour stays the same for Pillow users having
+ImageMagick installed.
+
 Saving TIFF with ICC profile
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -86,3 +98,12 @@ PyQt6
 
 Support has been added for PyQt6. If it is installed, it will be used instead of
 PySide6, PyQt5 or PySide2.
+
+GraphicsMagick
+^^^^^^^^^^^^^^
+
+The test suite can now be run on systems which have GraphicsMagick_ but not
+ImageMagick_ installed.  If both are installed, the tests prefer ImageMagick.
+
+.. _GraphicsMagick: http://www.graphicsmagick.org/
+.. _ImageMagick: https://imagemagick.org/

src/PIL/ImageShow.py

@@ -194,6 +194,15 @@ def get_command_ex(self, file, **options):
         return command, executable
 
 
+class GmDisplayViewer(UnixViewer):
+    """The GraphicsMagick ``gm display`` command."""
+
+    def get_command_ex(self, file, **options):
+        executable = "gm"
+        command = "gm display"
+        return command, executable
+
+
 class EogViewer(UnixViewer):
     """The GNOME Image Viewer ``eog`` command."""
 
@@ -220,6 +229,8 @@ def get_command_ex(self, file, title=None, **options):
 if sys.platform not in ("win32", "darwin"):  # unixoids
     if shutil.which("display"):
         register(DisplayViewer)
+    if shutil.which("gm"):
+        register(GmDisplayViewer)
     if shutil.which("eog"):
         register(EogViewer)
     if shutil.which("xv"):