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In A,The shaded portion of the picture represents an image,the blue dotted box indicates the area I want to crop.
I want a picture like B,the white space is transparent,But I can only get a picture of what C looks like,image pixels are always filled from the top.
The command I'm using looks something like this:
convert 32.jpg -crop 356x768+436+263 -background transparent -extent 356x768 output.png