Thanks for the helpful information. Fair enough, but why doe PI use "mirror" when everyone else uses "flip"- and why, if I have a "horizontal mirror" - does the image actually flip left to right? Try a horizontal mirror on a desk and in the real world the image is actually flipped top to bottom. Also, yes, good to have this in "IMAGE", a processing menu, but this has the potential for altering (if I am not careful to cancel save) my original images when all I want to do is view (e.g. "BLINK" which I use all the time) them in the orientation of my choice. We really need the facility in the entirely volatile "VIEW" menu. I find this way of handling "flip" surprising given the PI philosophy on other "VIEW" options, particularly "STF" (but also e.g. "Zoom") should NOT alter the original image unless expressly commanded.
I try to like PixInsight, but it's hard given the insistence of doing things in a non-intuitive way, using non-standard terminology and with (STILL) very incomplete documentation.