DM-48704: Invert negative footprints for deblending in DIA

python/lsst/ip/diffim/detectAndMeasure.py

@@ -526,13 +526,35 @@ def makeFootprints(sources):
             footprints.setFootprints([src.getFootprint() for src in sources])
             return footprints
 
-        def deblend(footprints):
+        def deblend(footprints, negative=False):
             """Deblend a positive or negative footprint set,
             and return the deblended children.
+
+            Parameters
+            ----------
+            footprints : `lsst.afw.detection.FootprintSet`
+            negative : `bool`
+                Set True if the footprints contain negative fluxes
+
+            Returns
+            -------
+            sources : `lsst.afw.table.SourceCatalog`
             """
             sources = afwTable.SourceCatalog(self.schema)
             footprints.makeSources(sources)
-            self.deblend.run(exposure=difference, sources=sources)
+            if negative:
+                # Invert the image so the deblender can run on positive peaks
+                difference_inverted = difference.clone()
+                difference_inverted.image *= -1
+                self.deblend.run(exposure=difference_inverted, sources=sources)
+                children = sources[sources["parent"] != 0]
+                # Set the heavy footprint pixel values back to reality
+                for child in children:
+                    footprint = child.getFootprint()
+                    array = footprint.getImageArray()
+                    array *= -1
+            else:
+                self.deblend.run(exposure=difference, sources=sources)
             self.setPrimaryFlags.run(sources)
             children = sources["detect_isDeblendedSource"] == 1
             sources = sources[children].copy(deep=True)
@@ -541,7 +563,7 @@ def deblend(footprints):
             return sources.copy(deep=True)
 
         positives = deblend(positiveFootprints)
-        negatives = deblend(negativeFootprints)
+        negatives = deblend(negativeFootprints, negative=True)
 
         sources = afwTable.SourceCatalog(self.schema)
         sources.reserve(len(positives) + len(negatives))

tests/test_detectAndMeasure.py

@@ -305,9 +305,33 @@ def test_detect_transients(self):
         kwargs["nSrc"] = 10
         kwargs["fluxLevel"] = 1000
 
+        blendedKwargs = kwargs
+        blendedKwargs["nSrc"] = 1
+
         # Run detection and check the results
         def _detection_wrapper(positive=True):
             transients, transientSources = makeTestImage(noiseLevel=noiseLevel, noiseSeed=8, **kwargs)
+            # Make a nearby transient source that doesn't fall off the image
+            # so we can test deblending
+            transientsBbox = transients.getBBox()
+            oneSourceX = transientSources[0].getX()
+            oneSourceY = transientSources[0].getY()
+            if oneSourceX < transientsBbox.getCenter()[0]:
+                blendedSourceX = oneSourceX + 10
+            else:
+                blendedSourceX = oneSourceX - 10
+            if oneSourceY < transientsBbox.getCenter()[1]:
+                blendedSourceY = oneSourceY + 10
+            else:
+                blendedSourceY = oneSourceY - 10
+            blendedTransients, blendedTransientSources = makeTestImage(noiseLevel=0,
+                                                                       noiseSeed=8,
+                                                                       xLoc=[blendedSourceX,],
+                                                                       yLoc=[blendedSourceY,],
+                                                                       **blendedKwargs)
+            blendedTransientSources["id"][0] = np.max(transientSources["id"]) + 1
+            transientSources.extend(blendedTransientSources)
+            transients.maskedImage += blendedTransients.maskedImage
             difference = science.clone()
             difference.maskedImage -= matchedTemplate.maskedImage
             if positive:
@@ -322,7 +346,7 @@ def _detection_wrapper(positive=True):
             refIds = []
             scale = 1. if positive else -1.
             for diaSource in output.diaSources:
-                self._check_diaSource(transientSources, diaSource, refIds=refIds, scale=scale)
+                self._check_diaSource(transientSources.copy(deep=True), diaSource, refIds=refIds, scale=scale)
         _detection_wrapper(positive=True)
         _detection_wrapper(positive=False)