Thanks for the updated and uncompressed image.
I measured the 20 micron line to be 216 pixels long.
So a micron is about 10.8 pixels in length.
So the wavelengths of visible light (0.38 - 0.74 microns) would be 4 to 8 pixels.
The highest theoretical resolution for an optical microscope is about 1/2 wavelength, or 0.2 microns, which is around 2 pixels. Of course, most microscopes don't have such a high resolution in practice, but some get close.
P.S. For the .jpg that Clay posted above, the 20 micron bar is about 97 pixels wide. So the pixel measurements are approximately one half the numbers above.
Last Edit: 8 months, 4 weeks ago by AnthonyYan. Reason: Added P.S.