problem has already been solved by the comments above,
but I tried changing png to 24bit bmp in Windows Painter
and using the bmp to polyline routine I wrote before.
(Input 255, 255, 255, 30% in exclusion color, keep true color)
left : true color, right : aci color for ctb
In this case, there is already a gradient hatch on the CAD
so there is no need to perform this additional process.
but this routine can be applied to any image and it doesn't matter what shape it is
Drawing2.dwg