How to match colors and tones of all images easily in Photoshop for color brightfield images (images of chromagenic-stained slides such as those prepared by histologists, e.g., H&E) and grayscale images from EM, etc. Not to be used for fluorescent images.
This function alone is a compelling reason to use Photoshop
How to Match Color in GIMP
No similar method exists to date (January 2019) in GIMP.
How to Match Color in Image J
No similar method exists to date (January 2019) in Image J.