You are correct. The fault was in the test image I was providing -- in this case a webcam view of my office.
Apologies. I completely failed to RTFM. Thanks again for an excellent tool.
Highlight Saturated Pixels
I was just browsing this thread and saw your request for an LG image. Here's one I took a while back. It's likely a combination of LG00 and LG05. I obtained it by deliberately misaligning the pump beam into an Nd:YAG NPRO laser. Sorry about the poor quality. Not much good for anything other than "looks cool" I'm afraid.