Index: trunk/ppImage/src/ppImageRebinReadout.c
===================================================================
--- trunk/ppImage/src/ppImageRebinReadout.c	(revision 37406)
+++ trunk/ppImage/src/ppImageRebinReadout.c	(revision 42382)
@@ -35,4 +35,8 @@
 
             // run the rebin code
+	    // XXX EAM 2022.04.21 : this function rebins the signal image and makes an attempt to
+	    // generate a mask only with bits raised in masked pixels that have > 50% of input pixels masked.
+	    // this step is very expensive because it must count the input mask bits for each pixel.
+	    // What is particularly silly is that the mask is not even used in the jpeg image.
             if (!pmReadoutRebin(outReadout, inReadout, options->maskValue, outFile->xBin, outFile->yBin)) {
                 psError(PS_ERR_UNKNOWN, false, "Unable to rebin readout.");