DxOMark has many unique features, two of which are that (1) we
perform sensor measurements on RAW images and (2) we test each
lens on every camera on which it can be mounted. Why do we do
this? A RAW image is the picture that is directly delivered by
the sensor. It is mostly unprocessed, and cannot be visualized
on directly on a screen. It has to be transformed by a fairly
complex signal processing known as RAW conversion. To answer
this question, consider the image as viewed by the end-user of a
camera. A color image is an array of pixels, each characterized
by its spatial position and three integer values that convey
intensities in three color channels—red, green, and blue. The
image "seen" by the sensor is completely different. Each
photosite, corresponding to a pixel in the final image, can see
only one type of color (either red, green, or blue). This means
that the signal perceived by the sensor has a single channel at
each pixel. The spatial distribution of the different color
channels is up to the sens