added new_from_image() to python

and tests

ChangeLog

@@ -2,6 +2,7 @@
 - supports fits images with leading non-image HDUs, thanks benepo
 - add vips_image_new_from_image() and vips_image_new_from_image1() ... make a
   constant image
+- add new_from_image() to Python as well
 
 23/4/17 started 8.5.5
 - doc polishing

TODO

@@ -1,13 +1,14 @@
-- can we change VImage::new_from_image() to not inherit bands? too awkward to
+- Add new_from_image() to C++
-  make a one-band image
 
-  needs some docs
+  needs docs
 
-  add to python, C, ruby, php etc etc
+  also check php, ruby
 
 - does cpp image.bandjoin(12) work? how about 
   bandjoin(std::vector<double>({1, 2}))
 
+  check bandjoin_const use in Python too
+
 - not sure about utf8 error messages on win
 
 - strange: 

doc/using-python.xml

@@ -162,8 +162,8 @@ im = Vips.Image.new_from_file(sys.argv[1], access = Vips.Access.SEQUENTIAL)
       for each file format. The C equivalent to this function,
       vips_image_new_from_file(), has more extensive documentation. Try
       <code>help(Vips.Image)</code> to see a list of all the image 
-      constructors --- you can load from memory, or create from an array, 
+      constructors --- you can load from memory, create from an array, 
-      for example. 
+      or create from a constant, for example. 
     </para>
 
     <para>

python/packages/gi/overrides/Vips.py

@@ -91,13 +91,7 @@ def imageize(match_image, value):
 
     # assume this is a pixel constant ... expand into an image using
     # match as a template
-    pixel = (Vips.Image.black(1, 1) + value).cast(match_image.format)
+    return match_image.new_from_image(value)
-    image = pixel.embed(0, 0, match_image.width, match_image.height,
-                        extend = Vips.Extend.COPY)
-    image = image.copy(interpretation = match_image.interpretation,
-                       xres = match_image.xres,
-                       yres = match_image.yres)
-    return image
 
 # we'd like to use memoryview to avoid copying things like ICC profiles, but
 # unfortunately pygobject does not support this ... so for blobs we just use
@@ -621,6 +615,29 @@ def add_doc(value):
 class Image(Vips.Image):
     # for constructors, see class methods above
 
+    def new_from_image(self, value):
+        """Create a new image based on an existing one.
+
+        A new image is created with the same width, height, format,
+        interpretation, resolution and offset as self, but with every pixel
+        having the value of value.
+
+        You can pass an array to create a many-band image.
+        """
+
+        # we'd like to call the vips function vips_image_new_from_image() but we
+        # can't call __getattr__ methods from a subclass 
+        pixel = (Vips.Image.black(1, 1) + value).cast(self.format)
+        image = pixel.embed(0, 0, self.width, self.height,
+                            extend = Vips.Extend.COPY)
+        image = image.copy(interpretation = self.interpretation,
+                           xres = self.xres,
+                           yres = self.yres,
+                           xoffset = self.xoffset,
+                           yoffset = self.yoffset)
+
+        return image
+
     # output
 
     def write_to_file(self, vips_filename, **kwargs):

test/test_iofuncs.py

@@ -62,5 +62,27 @@ class TestIofuncs(unittest.TestCase):
         for case in cases:
             self.assertEqualObjects(split(case[0]), case[1])
 
+    def test_new_from_image(self):
+        im = Vips.Image.mask_ideal(100, 100, 0.5, reject = True, optical = True)
+
+        im2 = im.new_from_image(12)
+
+        self.assertEqual(im2.width, im.width)
+        self.assertEqual(im2.height, im.height)
+        self.assertEqual(im2.interpretation, im.interpretation)
+        self.assertEqual(im2.format, im.format)
+        self.assertEqual(im2.xres, im.xres)
+        self.assertEqual(im2.yres, im.yres)
+        self.assertEqual(im2.xoffset, im.xoffset)
+        self.assertEqual(im2.yoffset, im.yoffset)
+        self.assertEqual(im2.bands, 1)
+        self.assertEqual(im2.avg(), 12)
+
+        im2 = im.new_from_image([1,2,3])
+
+        self.assertEqual(im2.bands, 3)
+        self.assertEqual(im2.avg(), 2)
+
+
 if __name__ == '__main__':
     unittest.main()