DxOMark Score for lens with camera

Camera Article
Motivation behind DxOMark Score | DxOMark Score design

DxOMark Score design

We considered the following requirements when designing DxOMark Score:

  • should be a single number,
  • averaged over the whole range of focal length
  • taking into account the best aperture
  • using only RAW measurements and is therefore independent of any RAW converter,
  • growing linearly with resolution, for a perfect optic and a noise-free signal,
  • growing linearly with the sensor dynamic range, measured in f-stops, for a perfect optic.

DxOMark Score can be interpreted as the maximum print size of the average quality. Obviously, any photo can be printed at any size, but beyond a certain point, a larger print does not reveal any additional details to an observer at close distance.

A DxOMark Score of 10 is high enough for an excellent 30x20cm print. When doubling each dimension (hence multiplying the print surface by four), the DxOMark Score should ideally be multiplied by four also. Typical correspondences are indicated in the table below.

Another element of DxOMark Score — part of its uniqueness as an image quality evaluation ranking system — is that we built it with the consideration that some camera flaws can be partially or completely corrected by digital processing (embedded in the camera, or performed on PC/MAC afterwards).

While the Sensor Overall Score describes the results of measurements only on sensors and is essentially related to image noise (for example, a difference of one f-stop offsets the Overall Sensor Score by approximately 15 points), the DxOMark Score is both proportional to resolution (taking optical aberrations into account) and to sensor dynamic range.

Summary

The purpose of a camera is to capture light reflected (or emitted) by the scene. More precisely, a camera capture the spatial organization of the scene, the amount of light at each point, as well as the colorimetric properties of this light. The greater a digital camera’s information capacity, the better its RAW output. DxOMark Score provides photographers with a powerful tool to evaluate this fundamentally important aspect of digital camera image quality performance.