Average of N integer images was overflowing data type

Fix #86

Author: PierreRaybaut

CHANGELOG.md

@@ -13,6 +13,7 @@ See DataLab [roadmap page](https://datalab-platform.com/en/contributing/roadmap.
   * This issue is related to [Issue #84](https://github.com/DataLab-Platform/DataLab/issues/84)
   * Adding the test data paths multiple times to `cdl.utils.tests.TST_PATH` was causing the test data to be loaded multiple times, which lead to some tests failing (a simple workaround was added to V0.16.2: this issue is now fixed)
   * Thanks again to [@rolandmas](https://github.com/rolandmas) for reporting the issue in the context of the Debian packaging
+* Fixed [Issue #86](https://github.com/DataLab-Platform/DataLab/issues/86) - Average of N integer images overflows data type
 
 ## DataLab Version 0.16.2 ##
 

cdl/core/gui/processor/base.py

@@ -584,10 +584,10 @@ def compute_n1(
             dst_gid = None
 
         for src_gid, dst_obj in dst_objs.items():
-            if is_integer_dtype(src_dtypes[src_gid]):
-                dst_obj.set_data_type(dtype=src_dtypes[src_gid])
             if func_objs is not None:
                 func_objs(dst_obj, src_objs[src_gid])
+            if is_integer_dtype(src_dtypes[src_gid]):
+                dst_obj.set_data_type(dtype=src_dtypes[src_gid])
             short_ids = [obj.short_id for obj in src_objs[src_gid]]
             dst_obj.title = f'{name}({", ".join(short_ids)})'
             group_id = dst_gid if dst_gid is not None else src_gid

cdl/tests/features/images/average_app_test.py

@@ -0,0 +1,46 @@
+# Copyright (c) DataLab Platform Developers, BSD 3-Clause license, see LICENSE file.
+
+"""
+Average application test
+========================
+
+The purpose of this test is to check that we can average a set of images without
+overflowing the data type.
+
+This test was written following a regression where the average of 10 images of
+size 256x256 with a Gaussian distribution of values was overflowing the data type
+uint8.
+"""
+
+# pylint: disable=invalid-name  # Allows short reference names like x, y, ...
+# pylint: disable=duplicate-code
+# guitest: show
+
+import numpy as np
+
+import cdl.obj
+import cdl.tests.data as ctd
+from cdl.tests import cdltest_app_context
+from cdl.utils.tests import check_array_result
+
+
+def test_image_average():
+    """Average application test."""
+    with cdltest_app_context() as win:
+        panel = win.imagepanel
+        N, size = 10, 256
+        dtype = cdl.obj.ImageDatatypes.UINT8
+        p = cdl.obj.NewImageParam.create(height=size, width=size, dtype=dtype)
+        data = ctd.create_2d_gaussian(size, np.dtype(dtype.value))
+        for _idx in range(N):
+            obj = cdl.obj.create_image_from_param(p)
+            obj.data = data
+            panel.add_object(obj)
+        panel.objview.select_groups([0])
+        panel.processor.compute_average()
+        res_data = panel.objview.get_sel_objects(include_groups=True)[0].data
+    check_array_result("Average", res_data, data)
+
+
+if __name__ == "__main__":
+    test_image_average()