added test test_stack_mean which was used to find bug in IJHyperstack.get_image

tests/improc_tests.py

@@ -6,7 +6,7 @@
 
 import unittest  # unittest2 doesn't exist in fiji
 import sys
-from lipase.imageengine import IImageEngine, PixelType, Aabb, NullDebugger, FileBasedDebugger
+from lipase.imageengine import IImageEngine, PixelType, Aabb, NullDebugger, FileBasedDebugger, StackImageFeeder
 from lipase.imagej.ijimageengine import IJImageEngine, IJImage
 from lipase.circsymdetector import create_circle_image
 
@@ -41,7 +41,22 @@ class ImProcTester(unittest.TestCase):
         print("measured_mean_value: %f" % measured_mean_value)
         self.assertAlmostEqual(measured_mean_value, expected_mean_value, delta=0.01)
 
-
+    def test_stack_mean(self):
+        ie = IImageEngine.get_instance()
+        num_channels = 4
+        width = 16
+        height = 16
+        offset_value = 42.0
+        stack = ie.create_hyperstack(width=width, height=height, num_channels=num_channels, num_slices=1, num_frames=1, pixel_type=PixelType.F32)
+        for channel_index in range(num_channels):
+            im = ie.create_image(width=width, height=height, pixel_type=PixelType.F32)
+            im.set_pixel(x=3, y=4, value=channel_index + offset_value)
+            stack.set_image(im, channel_index=channel_index)
+        mean_image = ie.compute_mean(StackImageFeeder(stack))
+        measured_avg = mean_image.get_mean_value()
+        sum_of_numbers = num_channels*(num_channels-1)/2 # sum of numbers from 0 to n = n * (n-1) / 2
+        expected_avg = (offset_value + float(sum_of_numbers)/num_channels)/(width*height)  
+        self.assertAlmostEqual(measured_avg, expected_avg, delta=0.0001)
 
 def run_script():
     print("executing run_script")