How to manually adjust tones in Photoshop for chromagenic-stained samples through a microscope (e.g., H&E). This is the White Eyedropper Method.
How to Adjust Manually using White Eyedropper Method in GIMP
Differs from Photoshop insofar as the Levels function differs:
• Set the White Output Value under Input Value to 94 (version 2.9). Click with white eyedropper tool on whitest background position on image.
• Click + symbol to save setting and apply that to other images.
How to Adjust Color Manually in Image J
No such tool exists in Image J. Use GIMP or Photoshop or Camera Raw.