Lens refraction depends on the wavelength. This means that
magnification not only depends on the image field position but
also on the light wavelength. A perfectly sharp edge going from
white to black yields a smooth transition showing the
decomposition of the light spectrum. This has two major effects
on the sensor. Each channel (usually R, G, B) is blurry because
it integrates a certain range of wavelengths that are imaged at
different positions on the sensor. Moreover, the different
channels are shifted with respect to one another. This usually
yields colored fringes along edges with a high level of
contrast. DxOMark measures the maximal shift between the three
color channels. This measure is a distance. LCA is expressed in
µm on 24x36 mm. 10 µm is a typical level of acceptability.
Lateral chromatic aberration is easily computed by considering
the image of a black spot on a white background. Mr is the
center of the spot in the red channel, Mg in the green channel,
Mb in the blue channel. LCA corresponds to