For different reference image?

Thank you very much for this nice repo.
I am also working on normalization. My problem is the reference image.
If the content of the reference image is different with the source image, how can I normalize brightness/illumination using histogram matching?

The issue names no files, tests, or entry points. Start by reviewing the repository's histogram-matching behavior and usage documentation, then clarify whether the missing outcome is guidance or a code change. Done requires a defined reference-image scenario and an agreed expected normalization result.

Written by the indexing model from the issue text.