Both Uses of

contrast
in
Nineteen Minutes

This relationship-four months old now-was still a mystery to her, as much as the constellation of freckles on Patrick's shoulders, the valley of his spine, the startling contrast of his black hair against a white sheet.
Chpt 2 *

contrast = notable difference

Judge Cormier looked about as inviting as a sheer cliff wall; by contrast, her daughter was shaking like a leaf.
Chpt 2 *

by contrast = in a comparison that shows differences

Definitions:

(1) (contrast as in: contrast their writing styles)
point to differences between; or compare to show differences
(2) (contrast as in: there is a contrast)
a difference -- especially a notable difference; or the side-x-side arrangement of things that draws attention to an unmissable difference
(3) (contrast as in: sharpen the picture contrast)
the difference between tones of an image -- as in a photo or video -- such as the quality of brightness or the intensity of shades or colors