The optical term “contrast” of an image is pretty much what we would expect from our daily use of the word.
The global contrast in the two images above is about the same, however the local contrast (the change from pixel to pixel) is less high in the lower image, because of the slight blurring.
The local contrast is described by the MTF-curve.
Yellow Writing on a white paper is nearly invisible on the image of a monochrome camera. Illumination with blue light increases the contrast nicely.
- Weber contrast
(Feature -background) / background
- Michelson contrast
Difference of intensities divided by sum of intensities. Often used in image processing.
- RMS contrast (Root Mean Square Contrast)
Standard deviation of the pixel intensities.