[magick-users] composite Dst_In transparency problem

[Günter Bachelier]

Hello,

I have a problem concerning composite: after the composing with
Dst_In the parts that were transparent in the mask were in the
result image black:

convert -size $triangle_widthx$triangle_width -stroke red -fill red
-draw "polyline 1,1 $triangle_width,$triangle_width 1,$triangle_width"
xc:none p4m_mask.png
convert -crop $triangle_widthx$triangle_width+$x4+$y4 image.jp2
image_p4m.png
composite p4m_mask.png image_p4m.png -compose Dst_In p4m_G1.png

A correction of the result with "-transparent black" would change all
parts.
How can the transparency be preserved?

Perhaps "-clip-mask" could be used, but I did not find a dokumentation
that helped me.


Thank you very much,
Günter