Question about sample script

Python: 3.8.10
OpenCV: 4.2.0

The sample python script I used:
I have tried both the OpenCV-built-in convertScaleAbs method and numpy.clip method provided in the script, however, they produce two different images.
I also tried “remove” the limit of numpy.clip by assigning them to extrem numbers, but got a third different iamge.

I have read about the source code, but stucked at convert_scale.dispatch.cpp#L99, I can’t find which function it really implement.