[davidmanze]

I do not know how it can be that you see the effect less on the image itself, Dave. I just did a small screen grab with my Mac and posted the resulting PNG.

 

  I haven't a clue either, but I did spend some minutes comparing..........maybe compression reared it's ugly head.

 

  I try to bring a little lightheartedness to the site..........hence this thread.........and some of my other jokey nonsense!

 

 

 Sometimes it's prudent to stand back and wait 15 minutes before clicking on the post button, it would have served well here!

 

 

 Edit:  I have since restudied the official Sigma image and cannot see any tangible purple artifacts!