Changeset 14824 for trunk/psModules/src/imcombine/pmSubtraction.c

Timestamp:

Sep 12, 2007, 10:21:41 AM (19 years ago)

Author:

Paul Price

Message:

The values in the variance map were about half of what they should
have been. Found that we need to normalise variance kernel so that
its sum is the square of the sum of the normal kernel --- simply
taking the square isn't enough. This corresponds to preserving the
relative scaling between the image and the weight map.

File:

• trunk/psModules/src/imcombine/pmSubtraction.c (modified) (2 diffs)

trunk/psModules/src/imcombine/pmSubtraction.c

@@ -4 +4 @@
  *  @author GLG, MHPCC
  *
- *  @version $Revision: 1.59 $ $Name: not supported by cvs2svn $
- *  @date $Date: 2007-09-10 20:10:05 $
+ *  @version $Revision: 1.60 $ $Name: not supported by cvs2svn $
+ *  @date $Date: 2007-09-12 20:21:41 $
  *
  *  Copyright 2004-2007 Institute for Astronomy, University of Hawaii
@@ -86 +86 @@
 
     // Take the square of the normal kernel
+    double sumNormal = 0.0, sumVariance = 0.0; // Sum of the normal and variance kernels
     for (int v = yMin; v <= yMax; v++) {
         for (int u = xMin; u <= xMax; u++) {
-            kernel->kernel[v][u] = PS_SQR(normalKernel->kernel[v][u]);
-        }
-    }
+            float value = normalKernel->kernel[v][u]; // Value of interest
+            float value2 = PS_SQR(value); // Value squared
+            sumNormal += value;
+            sumVariance += value2;
+            kernel->kernel[v][u] = value2;
+        }
+    }
+
+    // Normalise so that the sum of the variance kernel is the square of the sum of the normal kernel
+    // This is required to keep the relative scaling between the image and the weight map
+    psBinaryOp(kernel->image, kernel->image, "*",
+               psScalarAlloc(PS_SQR(sumNormal) / sumVariance, PS_TYPE_F32));
 
     return kernel;