Fix fitz.Pixmap colorspace conversion.

Constructor `Pixmap(colorspace, pixmap)` previously always incorrectly
converted via a greyscale proofing colorspace.

Fixed similar bug in `Page.insert_image()` if we process the pixmap.

Also fixed creation of `Colorspace` from a `mupdf.FzColorspace` - this would
previously always created a RGB `Colorspace`.

Address #3058

src/__init__.py

@@ -2396,7 +2396,9 @@ class Colorspace:
 
     def __init__(self, type_):
         """Supported are GRAY, RGB and CMYK."""
-        if type_ == CS_GRAY:
+        if isinstance( type_, mupdf.FzColorspace):
+            self.this = type_
+        elif type_ == CS_GRAY:
             self.this = mupdf.FzColorspace(mupdf.FzColorspace.Fixed_GRAY)
         elif type_ == CS_CMYK:
             self.this = mupdf.FzColorspace(mupdf.FzColorspace.Fixed_CMYK)
@@ -7759,8 +7761,8 @@ def _insert_image(self,
                 else:
                     pm = mupdf.fz_convert_pixmap(
                             arg_pix,
-                            mupdf.FzColorspace(0),
-                            mupdf.FzColorspace(0),
+                            mupdf.FzColorspace(),
+                            mupdf.FzColorspace(),
                             mupdf.FzDefaultColorspaces(None),
                             mupdf.FzColorParams(),
                             1,
@@ -9429,7 +9431,7 @@ def __init__(self, *args):
                 self.this = mupdf.fz_convert_pixmap(
                         spix,
                         cs,
-                        mupdf.FzColorspace(0),
+                        mupdf.FzColorspace(),
                         mupdf.FzDefaultColorspaces(None),
                         mupdf.FzColorParams(),
                         1

tests/test_pixmap.py

@@ -187,3 +187,23 @@ def product(x, y):
         pix.save(os.path.abspath(f'{__file__}/../../tests/test_3050_out.png'))
         assert digest1 != digest0
         assert digest1 == digest_expected
+
+def test_3058():
+    doc = fitz.Document(os.path.abspath(f'{__file__}/../../tests/resources/test_3058.pdf'))
+    images = doc[0].get_images(full=True)
+    pix = fitz.Pixmap(doc, 17)
+
+    # First bug was that `pix.colorspace` was DeviceRGB.
+    assert str(pix.colorspace) == 'Colorspace(CS_CMYK) - DeviceCMYK'
+
+    pix = fitz.Pixmap(fitz.csRGB, pix)
+    assert str(pix.colorspace) == 'Colorspace(CS_RGB) - DeviceRGB'
+
+    # Second bug was that the image was converted to RGB via greyscale proofing
+    # color space, so image contained only shades of grey. This compressed
+    # easily to a .png file, so we crudely check the bug is fixed by looking at
+    # size of .png file.
+    path = os.path.abspath(f'{__file__}/../../tests/test_3058_out.png')
+    pix.save(path)
+    s = os.path.getsize(path)
+    assert 1800000 < s < 2600000, f'Unexpected size of {path}: {s}'