Here is the gm identify on the original PNG:
foo.png PNG 640x480+0+0 DirectClass 8-bit 23.2K 0.000u 0:01
The resulting footrim.png from ImageMagick:
* successfully trimmed to 613x400 (from 640x480)
The following command fails to trim a PNG that can be trimmed using ImageMagick's "convert.exe -trim" command:
gm convert -trim foo.png footrim.png
The resulting footrim.png from GraphicsMagick:
1. has same dimension 640x480 as original
2. interestingly, it has smaller file size (16,535 bytes vs original 23,724 bytes)
NOTE: using -fuzz didn't make any difference (I tried up to 50%).
I'm using GraphicsMagick 1.3.14 2012-02-25 Q16 (pre-built binary download) on Windows 7 x64 with AMD Phenom processor.
I'm unable to share the PNG because I don't have permission to distribute it. It has a black rectangle frame 613x400 inside a 640x480 white background The black rectangle frame is at least 5 pixels thick. All four corners and the margin surrounding the rectangle are white.
I hope this bug is fixed, trim is the most important feature to us and I prefer GraphicsMagick's emphasis on performance and security...