Transparent was deprecated years ago in favor of Alpha Channels wasn’t it…
I have code I wrote in 2016, where that was used, but even though the code was never recompiled, once I installed Mojave, that feature didn’t seem to work anymore.
Michel… here is some code that will make a mask for a PNG
Dim f As FolderItem
Dim p As picture
dim m as picture
Dim pg As graphics
Dim p_rgb As RGBSurface
Dim m_rgb As RGBSurface
p=picture.Open(f)
pg=p.Graphics
m=new picture(p.Width,p.Height)
//
p_rgb=p.RGBSurface
m_rgb=m.Rgbsurface
m_rgb.FloodFill(0,0,color.white)
For x=0 To pg.Width
For y=0 To pg.Height
if p_rgb.pixel(x,y)=color.white then continue
m_rgb.pixel(x,y)=&c000000
Next y
Next x
p.ApplyMask(m)
p.Save(f,picture.SaveAsPNG)