How to crop an image in Graphics Magick?

Question

JPEG

The input formats are:
- jpeg (which, in general, do not need to be cut);
- png, some of which have a transparent background and need to be clipped, here's an example .
After processing, the images are saved in jpeg format with a black background and a fixed size (if the source was a transparent png).
The use of "-trim" does not give the desired result: png with transparency are cropped as it should, but images with a uniform background fall under the distribution, and often cut off huge pieces from the image.
I tried the "-border 1x1 -bordercolor transparent -trim" combo, partially solved the problem, but images containing an overwhelming amount of black (on the edges and in the center) are trimmed to 0x0, resulting in just a black image of the set size on the output. I understand that "-bordercolor transparent" does not give the desired effect and the border turns out to be black in reality, then trimming occurs in black - that's why we have a black image. Preset "-background transparent" didn't help.
How can I cut off only the transparent area of ​​a png?
GraphicsMagick 1.3.12, NodeJS, I use this module, I set commands via gm.in().

Answer 1

Through trial and error, a solution was found. In order for "-bordercolor transparent" to be truly transparent, you must first add a matte channel with the "-matte" command