An example of such a testchart is illustrated in Figure 1.įigure 1 : Output image of the camera-under-test observing the Siemens star. The basic idea is to use a single testchart with a co-called Siemens-star. The method described here is based on the work of Anke Neumann, written down in her MSc thesis “Verfahren zur Aufloesungsmessung digitaler Kameras”, June 2003. And the values obtained for the CTF will be larger than the ones obtained for the MTF. In the case a square-wave pattern is used, not the MTF but the CTF (= Contrast Transfer Function) will be measured. It should be noted that in this case dedicated testcharts are used to measure the MTF, but the pattern on the chart should sinusoidally change between dark parts and light parts. In this first MTF-blog the measurement of the modulation transfer function based on imaging with a sine-wave pattern will be discussed. Even the effect of the processing of the sensor’s signal can have an influence on the MTF, and will be include in the measurement. It should be noted that all method listed, except the “laser-speckle technique, measure the MTF of the complete imaging system : all parts of the imaging system are included, such as lens, filters (if any present), cover glass and image sensor. Various methods can be used to characterize the MTF, such as the “slit image”, the “knife edge”, the “laser-speckle technique” and “imaging of sine-wave patterns”. The MTF is not really the most easiest measurement that can be done on an imaging system. In technical terms, the MTF is the magnitude of the optical transfer function, being the Fourier transform of the response to a point illumination. The latter can be an image sensor, a lens, a mirror or the complete camera. In a simple wording, the modulation transfer function or MTF is a measure of the spatial resolution of an imaging component.
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