Converted the jpeg files used in image and pixel group tests to png.

The system jpeg library on the Mac is now different from that on
Linux, and tests that rely on the exact RGB values of voxels will
fail on one platform or the other (unless vtk on the Mac is compiled
so that it uses its own jpeg library, instead of the system library).
This is an attempt to avoid the problem entirely by using png files
instead of jpeg.

Author: snarkhunter

TEST3D/image_test.py

@@ -290,16 +290,19 @@ def Load(self):
                                depth_in_pixels=100)
         OOF.File.Load.Image(
             filenames=ThreeDImageDirectory(
-                directory=reference_file("ms_data","jpeg"),
+                # directory=reference_file("ms_data","jpeg"),
+                directory=reference_file("ms_data","megavoxel"),
                 sort=NumericalOrder()),
             microstructure="load_test",
             height=automatic, width=automatic, depth=automatic)
         ms = getMicrostructure("load_test")
         ms_images = ms.imageNames()
         self.assertEqual(len(ms_images),1)
-        self.assert_("jpeg" in ms_images)
+        # self.assert_("jpeg" in ms_images)
+        self.assert_("megavoxel" in ms_images)
         # Check a few pixel values
-        im = imagecontext.imageContexts['load_test:jpeg'].getObject()
+        #im = imagecontext.imageContexts['load_test:jpeg'].getObject()
+        im = imagecontext.imageContexts['load_test:megavoxel'].getObject()
         self.assertEqual(im[primitives.iPoint(0,0,0)],
                          color.RGBColor(0.054901960784313725,
                                         0.996078431372549,
@@ -312,19 +315,25 @@ def Load(self):
         # pixel_test.py on Mac but not Linux.  Apparently Mac and
         # Linux use different jpeg libraries which decompress images
         # differently. WTF?
-        ## TODO: Check that problem is avoided if vtk on Mac is
-        ## compiled with USE_SYSTEM_JPEG=OFF
+        # The problem is avoided if vtk on Mac is
+        # compiled with USE_SYSTEM_JPEG=OFF
         self.assertEqual(im[primitives.iPoint(16, 9, 99)],
                          # Linux value
-                         color.RGBColor(
-                             0.3058823529411765,
-                             0.9921568627450981,
-                             0.7215686274509804)
+                         # color.RGBColor(
+                         #     0.3058823529411765,
+                         #     0.9921568627450981,
+                         #     0.7215686274509804)
                          # Mac value
                          # color.RGBColor(
                          #     0.2901960784313726,
                          #     1.0,
                          #     0.7372549019607844)
+
+                         # After converting to PNG
+                         color.RGBColor(
+                             0.2901960784313726,
+                             1.0,
+                             0.7372549019607844)
         )
 
     ## Check that an Image saved in a Microstructure data file is