Magenta star halos are normal, alas
It takes some effort to get rid of them.
To apply the screen stretch to the image is pretty easy but complicated to explain... First make sure you have STF set up to track the currently selected image: the tick box at bottom right should be enabled. Now click on your screen stretched image (STF will now reflect the screen stretch parameters.) Bring up the HistogramTransformation process, click and hold the new instance triangle on STF and drag and drop it on the bottom bar of the HT process (the bar with the new instance triangle, apply square, etc.) You should see a stretch appear in the bottom panel of HT. Now apply this stretch to your image by clicking and holding the new instance triangle on HT and drag and drop it on your image. The image will turn completely white because it now has an image stretch and a screen stretch applied to it. Turn off the screen stretch by right clicking on the image and selecting Screen Transfer Functions->Reset STF. Voila!
Cheers,
Rick.