Linearisation

The resolution measurement with sinusoidal Siemens stars is applicable to all digital cameras and done within minutes.

OECF patches
Example: 16 OECF-patches around a Siemens-Star



Linearisation by means of the OECF is obtained as follows

1. Measuring the actual OECF
The density is measured at each gray patch and applied to an Input / Output-graph. A poly-fit connects the points to a curve.
2. Inverting the measured OECF
The measuring points are converted and again connected by a poly-fit. So you get exactly the inverted curve.
3. Linearisation
By multiplying measured and inverted OECF-curve you get a linear curve
measured OECF inverted OECF linearised curve
measured OECF inverted OECF linear OECF


The linearised data can be applied for resolution measurement.

In case of a resolution measurement with a Siemens-Star, the modulation in the low frequencies (those are the white and black patch right to the star) has to be 1. With higher frequencies it decreases and goes down to 0, where no linepairs can be resolved anymore. The modulation is calculated as follows:
modulation

So you can see that it is neccessary to have Imin = 0, otherwise the modulation could not get 1. A modulation of 1 can be reached by shifting the OECF-curve. *

dynamic range
Dynamic Range of a camera

* For detailed information please download our conference paper ยป

cs