Microtek ArtixScan M1 Pro User Manual page 39

Use the Gradation tool to adjust the
midtones of the lightness channel "L" of
an image.
In the example below, the original is
underexposed, with the middle tones of
the image being too dark. The corrected
image shows the middle tones being
brightened, but the saturation and hues of
the image remain untouched.