Merge pull request #446 from LSSTDESC/u/jchiang/bleed_trail_neg_pixels

Fix negative pixels that could happen from bleed trails

Author: jchiang87

imsim/bleed_trails.py

@@ -144,7 +144,7 @@ def __call__(self, ypix):
             # Off the bottom end, the charge escapes into the electronics.
             # We can reduce the excess charge by one full-well-worth.
             # These electrons are not added to any pixel though.
-            self.excess_charge -= self.full_well
+            self.excess_charge -= min(self.full_well, self.excess_charge)
         else:
             # Electrons do not escape off the top end, so excess charge is not reduced
             # when trying to bleed past the end of the channel.

imsim/lsst_image.py

@@ -1,4 +1,5 @@
 import numpy as np
+import hashlib
 import logging
 import galsim
 from galsim.config import RegisterImageType, GetAllParams, GetSky, AddNoise
@@ -298,11 +299,15 @@ def addNoise(self, image, config, base, image_num, obj_num, current_var, logger)
             camera = get_camera(self.camera_name)
             det_name = base['det_name']
             serial_number = camera[det_name].getSerial()
+            # Note: the regular Python hash function is non-deterministic, which is not good.
+            # Instead we use hashlib.sha256, which is deterministic and convert that to an integer.
+            # https://stackoverflow.com/questions/27954892/deterministic-hashing-in-python-3
+            seed = int(hashlib.sha256(serial_number.encode('UTF-8')).hexdigest(), 16) & 0xFFFFFFFF
             # Only apply fringing to e2v sensors.
             if serial_number[:3] == 'E2V':
                 ccd_fringing = CCD_Fringing(true_center=image.wcs.toWorld(image.true_center),
                                             boresight=self.boresight,
-                                            seed=hash(serial_number), spatial_vary=True)
+                                            seed=seed, spatial_vary=True)
                 ny, nx = sky.array.shape
                 xarr, yarr = np.meshgrid(range(nx), range(ny))
                 logger.info("Apply fringing")

imsim/stamp.py

@@ -303,7 +303,7 @@ def _getGoodPhotImageSize1(self, obj, keep_sb_level, pixel_scale):
                 else:
                     obj_list.append(item)
             obj = galsim.Add(obj_list)
-        elif isinstance(obj.original, galsim.RandomKnots):
+        elif hasattr(obj, 'original') and isinstance(obj.original, galsim.RandomKnots):
             # Handle RandomKnots object directly
             obj = obj.original._profile
 

tests/data/neg_pixel_bleed.pickle

@@ -2,6 +2,8 @@
 Unit tests for bleed trail implementation.
 """
 import unittest
+from pathlib import Path
+import pickle
 import numpy as np
 import galsim
 import imsim
@@ -64,6 +66,17 @@ def test_bleed_channel(self):
         # Check that bleed trail is centered on original star.
         self.assertLessEqual(np.abs(star_center - (nmin + nmax)/2), 1)
 
+    def test_bleed_channel_no_negative_pixels(self):
+        """This is a reproducer for a case found from running the
+        code for ComCam simulations."""
+        # Read in the channel data and full well used.
+        DATA_DIR = Path(__file__).parent / 'data'
+        neg_pixel_data = str(DATA_DIR / 'neg_pixel_bleed.pickle')
+        with open(neg_pixel_data, "rb") as fobj:
+            channel_data, full_well = pickle.load(fobj)
+        bled_channel = imsim.bleed_channel(channel_data, full_well)
+        self.assertTrue(all(bled_channel > 0))
+
     def test_find_channels_with_saturation(self):
         """
         Test the function to find channels in an image that have pixels

tests/test_bleed_trails.py

@@ -1,4 +1,5 @@
 import numpy as np
+import hashlib
 import pytest
 from imsim import make_batoid_wcs, CCD_Fringing, get_camera
 import galsim
@@ -18,6 +19,7 @@ def test_fringing():
     camera = get_camera()
     det_name = 'R22_S11'
     serial_num = camera[det_name].getSerial()
+    seed = int(hashlib.sha256(serial_num.encode('UTF-8')).hexdigest(), 16) & 0xFFFFFFFF
 
     xarr, yarr = np.meshgrid(range(4096), range(4004))
 
@@ -41,7 +43,7 @@ def test_fringing():
 
     ccd_fringing = CCD_Fringing(true_center=image.wcs.toWorld(image.true_center),
                                 boresight=world_center,
-                                seed=hash(serial_num), spatial_vary=True)
+                                seed=seed, spatial_vary=True)
     # Test zero value error
     with pytest.raises(ValueError):
         ccd_fringing.calculate_fringe_amplitude(xarr, yarr, amplitude=0)
@@ -91,7 +93,7 @@ def test_fringing():
 
     ccd_fringing_1 = CCD_Fringing(true_center=image.wcs.toWorld(image.true_center),
                                 boresight=world_center,
-                                seed=hash(serial_num), spatial_vary=False)
+                                seed=seed, spatial_vary=False)
     fringe_map1 = ccd_fringing_1.calculate_fringe_amplitude(xarr,yarr)
 
     # Try another random location on the focal plane.
@@ -101,7 +103,7 @@ def test_fringing():
 
     ccd_fringing_2 = CCD_Fringing(true_center=image.wcs.toWorld(image.true_center),
                                 boresight=world_center,
-                                seed=hash(serial_num), spatial_vary=False)
+                                seed=seed, spatial_vary=False)
     fringe_map2 = ccd_fringing_2.calculate_fringe_amplitude(xarr,yarr)
     # Check if the two fringing maps are indentical.
     if np.array_equal(fringe_map1,fringe_map2) != True: