How to match tones manually in Photoshop from images taken through a microscope or from another source.
How to Adjust Tones Manually in GIMP
Works similarly to Photoshop except:
• Sample points are made by holding down Control/Command key and dragging “guideline” from ruler area.
• Levels are found under Color. Click Logarithmic icon (far right at top) and then match black level slider and white level slider to ends of the histogram.
• Settings are saved by clicking the + symbol in the Levels box.
How to Adjust Tones Manually in Image J
Not recommended for color, brightfield images. However, tones in grayscale images can be set BUT change Look Up Table (LUT) to HiLo to view saturated pixels (red color = too bright, blue color = too dark): Image > Look Up Tables > HiLo. Use Windows/Levels under Image > Adjust.
ABSOLUTELY set Appearance in Image J or image will not appear visually correct: Under Edit > Options > Appearance choose correct bit depth to match image (bit depth can be found under Image > Show Info).