Both Uses of

contrast
in
Murder On The Orient Express

By contrast the noises on the train seemed unusually loud.
Chpt 1.5 *

by contrast = in a comparison that shows differences

Poirot's methods with Hildegarde Schmidt were a complete contrast to his handling of Mary Debenham.
Chpt 2.12 *

contrast = something notably different compared (to something)

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