[MACTCL] Alpha/Transparency of PNGs problems Tk 8.6.6

[Andy C. <an...@ac...>]

Alpha/Transparency of PNGs is not working correctly for me under Tk8.6.6.

 

It's fine under Windows; incorrect but not too bad on some Macs; awful on
other Macs.

 

Windows - fine with perfect transparency:
http://www.inivis.com/external/badpngwin.png

MacOS Sierra 10.12.? Newish Mac (wrong transparency levels but not corrupt):
http://www.inivis.com/external/badpngmed.png

MacOS sierra 10.12.1  2011 Mac Mini (very bad - corrupt background where it
should be transparent):  http://www.inivis.com/external/badpngsierra.png

 

The images are made with "image create photo <name> -file <filename>" from
png files.

 

I found some earlier references to transparency problems but that was some
time ago - is here a fix for this?