fix hist_entropy

there was a copy-paste error in the call to vips_log(), thanks Lovell

see https://github.com/lovell/sharp/issues/295

ChangeLog

@@ -1,6 +1,7 @@
 27/1/16 started 8.2.3
 - fix a crash with SPARC byte-order labq vips images
 - fix parsing of filenames containing brackets, thanks shilpi230
+- fix hist_entropy (lovell)
 
 12/1/16 started 8.2.2
 - changes to ease compiling C++ binding with MSVC [Lovell Fuller]

libvips/histogram/hist_entropy.c

@@ -3,6 +3,8 @@
  * Author: John Cupitt
  * 11/8/15	
  * 	- from hist_ismonotonic.c
+ * 6/3/16
+ * 	- vips_log() call was mangled, thanks Lovell
  */
 
 /*
@@ -80,7 +82,7 @@ vips_hist_entropy_build( VipsObject *object )
 		return( -1 );
 	sum = avg * VIPS_IMAGE_N_PELS( entropy->in ) * entropy->in->Bands;
 	if( vips_linear1( entropy->in, &t[0], 1.0 / sum, 0, NULL ) ||
-		vips_log( t[0], &t[1], 1.0 / sum, 0, NULL ) ||
+		vips_log( t[0], &t[1], NULL ) ||
 		vips_linear1( t[1], &t[2], 1.0 / log( 2.0 ), 0, NULL ) ||
 		vips_multiply( t[0], t[2], &t[3], NULL ) ||
 		vips_avg( t[3], &avg, NULL ) )

test/test_histogram.py

@@ -101,7 +101,7 @@ class TestHistogram(unittest.TestCase):
 
         self.assertEqual((im - im2).abs().max(), 0.0)
 
-    def test_hist_map(self):
+    def test_percent(self):
         im = Vips.Image.new_from_file("images/IMG_4618.jpg").extract_band(1)
 
         pc = im.percent(90)
@@ -112,6 +112,13 @@ class TestHistogram(unittest.TestCase):
 
         self.assertAlmostEqual(pc_set, 90, places = 0)
 
+    def test_hist_entropy(self):
+        im = Vips.Image.new_from_file("images/IMG_4618.jpg").extract_band(1)
+
+        ent = im.hist_find().hist_entropy()
+
+        self.assertAlmostEqual(ent, 4.367, places = 3)
+
     def test_stdif(self):
         im = Vips.Image.new_from_file("images/IMG_4618.jpg")