Bug in PNG coder?

[el_supremo]

I've been trying to get my MagickWand Examples in C up to date. Most of the examples work fine (in V6.9.7) but a couple related to transparency give oddball results.
Fortunately, I can demonstrate the problem with the command line.
This command should change all the white pixels to be transparent, including those in the Wizard's beard.

Code: Select all

imconvert logo: -alpha set -channel RGBA -fuzz 1% -fill none -transparent white logo_transp.png

It works with 6.4.2 Q8 (on win7 x64) but with 6.9.7 Q16 and 7.0.5 Q16 (both on Win10 x64) it does not change the white pixels. I tried a few other variations of the command to see if I could get the alpha channel to show up but to no avail. The two obvious differences are that 6.4.2 is a much earlier version than the others and also it is Q8. I haven't got an early Q16 version that I can try.
However, if I just change the output filename such that it writes a GIF or TIFF, both formats work with V6.9.7 and V7.0.5 which leads me to suspect that the problem lies in the PNG coder.

Pete

[dlemstra]

I am getting the correct image with the latest beta under Windows. Can you share your output image?

p.s. The link in your signature seems broken.

[el_supremo]

Hmmmm. It just occurred to me to wonder if it is PSP that isn't displaying it properly and lo and behold, MagicViewer displays it with transparency but PSP Pro X9 doesn't.
Weird.
Apparently it's nothing to do with the PNG coder in IM. It's the PNG decoder in PSP!

Thanks for making me look outside the box

Pete
P.S. I've fixed up my sig.