  Compared with raw images, the more common JPEG images are less useful for
machine vision algorithms and professional photographers because JPEG-sRGB does
not preserve a linear relation between pixel values and the light measured from
the scene. A camera is said to be radiometrically calibrated if there is a
computational model which can predict how the raw linear sensor image is mapped
to the corresponding rendered image (e.g. JPEGs) and vice versa. This paper
begins with the observation that the rank order of pixel values are mostly
preserved post colour correction. We show that this observation is the key to
solving for the whole camera pipeline (colour correction, tone and gamut
mapping). Our rank-based calibration method is simpler than the prior art and
so is parametrised by fewer variables which, concomitantly, can be solved for
using less calibration data. Another advantage is that we can derive the camera
pipeline from a single pair of raw-JPEG images. Experiments demonstrate that
our method delivers state-of-the-art results (especially for the most
interesting case of JPEG to raw).
