On each object is measured :
- g = gravity centre
- s = surface area (by counting the number of pixels composing object)
- L and l = long and short axes of the best fitting ellipse
- a = angle between the long axis and horizontality
- p = perimeter (by counting the number of pixels at the object boundary)
For details, see the manual of NIH Image available at http://rsb.info.nih.gov/nih-image/
Measurements are then exported to a spreadsheet for further processing.
Do = equivalent disk diameter =
The following simplifications need to be considered:
- grains are not spherical
- random two-dimensional section of grains leads to an underestimation of grain diameter.
P% provides the amount of "coarse" grains compared to a clay matrix.
By plotting P% calculated on each pixels row as a function of the depth of its centre of gravity, it is possible to detect any graded-bedding.
each object receives a weighed coefficient pi = (L/l) (Do)
Inclination diagrams are build as traditional rose diagrams. In this example, the inclination class at 35° receives the strongest value. In the original BSE image, this orientation of the grain is perceptible. There is 18 inclination classes.
Q measures the objects majority orientation
S indicates the strength of the parallelism between objects
For the example, Q = 12° and S = 0.8
Rm = mean Ri
Ri = 4 area/p L2
Sediments composed with numerous elongated objects (as micas) have weak Rm
For the example, Rm = 0.58
Using indices, it is possible to quantify most of the aspects the sedimentary facies.