Error when chop after trim

[kivist]

Code (test.png is shown above) run in cmd
(I'm not pro so I don't know how to paste good looking codes- -):
line1: convert test.png -trim test.png
line2: convert test.png -gravity East -chop 3x0 test.png

Line2 returns error :
"convert.exe: geometry does not contain image `test.png' @ warning/transform.c/ChopImage/225."

Environment:
Surface pro 3 i5 16G mem
Windows 10 x64 build 10240
ImageMagick-6.9.1-9-Q16-x64-dll.exe

[urban-warrior]

Try this:

convert test.png -trim +repage -gravity East -chop 3x0 test.png

[kivist]

Issue solved.

Now I know the meaning of
"Here we trim the image, but only to list the result on what part of the image was trimmed, not the actual trimmed image. "

However, is it possible to add a warning like "Cannot chop an image with canvas info" when this kind of stupid mistake was made by amateurs like me?

Thanks very much.

[urban-warrior]

You actually can chop an image with a virtual canvas, it may give unexpected results unless you take into account the virtual canvas geometry.