Unit of dynamic range
Ξ January 11th, 2008 | → 0 Comments | ∇ Tutorials |
The dynamic range is the ratio between the maximum and minimum values of a physical measurement. Its definition depends on what the dynamic range refers to.
For a scene: ratio between the brightest and darkest parts of the scene.
For a camera: ratio of saturation to noise. More specifically, ratio of the intensity that just saturates the camera to the intensity that just lifts the camera response one standard deviation above camera noise.
For a display: ratio between the maximum and minimum intensities emitted from the screen.
Dynamic range is a ratio and as such a dimensionless quantity. In photography and imaging, the dynamic range represents the ratio of two luminance values, with the luminance expressed in candelas per square meter.
The range of luminance human vision can handle is quite large. While the luminance of starlight is around 0.001 cd/m2, that of a sunlit scene is around 100,000 cd/m2, which is hundred millions times higher. The luminance of the sun itself is approximately 1,000,000,000 cd/m2. The human eye can accommodate a dynamic range of approximately 10,000:1 in a single view.
To more easily represent such different values, it is common to use a logarithmic scale to plot the luminance. The scanline below represents the log base 10 of the luminance, so going from 0.1 to 1 is the same distance as going from 100 to 1000, for instance.
A scene showing the interior of a room with a sunlit view outside the window, for instance, will have a dynamic range of approximately 100,000:1.