Support Pillow mode "RGBa"

For Pixmap image output via Pillow, also support mode RGBa with the new keyword parameter "unmultiply". The Pillow image will then be created with unmultiplied pixels.

fitz/fitz.i

@@ -8136,7 +8136,7 @@ Args:
     alphavalues: (bytes) with length (width * height) or 'None'.
     premultiply: (bool, True) premultiply colors with alpha values.
     opaque: (tuple, length colorspace.n) this color receives opacity 0.
-    matte: (tuple, length colorspace.n)) preblending background color.
+    matte: (tuple, length colorspace.n) preblending background color.
 """)
         PyObject *set_alpha(PyObject *alphavalues=NULL, int premultiply=1, PyObject *opaque=NULL, PyObject *matte=NULL)
         {
@@ -8447,17 +8447,20 @@ def save(self, filename, output=None, jpg_quality=95):
         self.set_dpi(self.xres, self.yres)
     return self._writeIMG(filename, idx, jpg_quality)
 
-def pil_save(self, *args, **kwargs):
+def pil_save(self, *args, unmultiply=False, **kwargs):
     """Write to image file using Pillow.
 
     Args are passed to Pillow's Image.save method, see their documentation.
     Use instead of save when other output formats are desired.
+
+    :arg bool unmultiply: generates Pillow mode "RGBa" instead of "RGBA".
+        Relevant for colorspace RGB with alpha only.
     """
     EnsureOwnership(self)
     try:
         from PIL import Image
     except ImportError:
-        print("PIL/Pillow not installed")
+        print("Pillow not installed")
         raise
 
     cspace = self.colorspace
@@ -8467,6 +8470,8 @@ def pil_save(self, *args, **kwargs):
         mode = "L" if self.alpha == 0 else "LA"
     elif cspace.n == 3:
         mode = "RGB" if self.alpha == 0 else "RGBA"
+        if mode == "RGBA" and unmultiply:
+            mode = "RGBa"
     else:
         mode = "CMYK"
 
@@ -8477,7 +8482,7 @@ def pil_save(self, *args, **kwargs):
 
     img.save(*args, **kwargs)
 
-def pil_tobytes(self, *args, **kwargs):
+def pil_tobytes(self, *args, unmultiply=False, **kwargs):
     """Convert to binary image stream using pillow.
 
     Args are passed to Pillow's Image.save method, see their documentation.
@@ -8486,7 +8491,7 @@ def pil_tobytes(self, *args, **kwargs):
     EnsureOwnership(self)
     from io import BytesIO
     bytes_out = BytesIO()
-    self.pil_save(bytes_out, *args, **kwargs)
+    self.pil_save(bytes_out, *args, unmultiply=unmultiply, **kwargs)
     return bytes_out.getvalue()
 
         %}