My camera has an engineering Dynamic Range of 14 stops, how many bits do I need to encode that DR? Well, to encode the whole Dynamic Range 1 bit could suffice, depending on the content and the application. The reason is simple, dynamic range is only concerned with the extremes, not with tones in between:
![\[ DR = \frac{Maximum Signal}{Minimum Signal} \]](https://i0.wp.com/www.strollswithmydog.com/wordpress/wp-content/ql-cache/quicklatex.com-f89166dae7cfbfc1a37b1ef0f536dd7e_l3.png?resize=194%2C41&ssl=1 "Rendered by QuickLaTeX.com")
So in theory we only need 1 bit to encode it: zero for minimum signal and one for maximum signal, like so
Imperfections in an imaging system’s capture process manifest themselves in the form of deviations from the expected signal. We call these imperfections ‘noise’ because they introduce grain and artifacts in our images. The fewer the imperfections, the lower the noise, the higher the image quality.
However, because the Human Visual System is adaptive within its working range, it’s not the absolute amount of noise that matters to perceived Image Quality (IQ) as much as the amount of noise relative to the signal – represented for instance by the Signal to Noise Ratio (SNR). That’s why to characterize the performance of a sensor in addition to signal and noise we also need to determine its sensitivity and the maximum signal it can detect.
In this series of articles I will describe how to use the Photon Transfer method and a spreadsheet to determine basic IQ performance metrics of a digital camera sensor. It is pretty easy if we keep in mind the simple model of how light information is converted into raw data by digital cameras:
Is MTF50 a good proxy for perceived sharpness? In this article and those that follow MTF50 indicates the spatial frequency at which the Modulation Transfer Function of an imaging system is half (50%) of what it would be if the system did not degrade detail in the image painted by incoming light.
It makes intuitive sense that the spatial frequencies that are most closely related to our perception of sharpness vary with the size and viewing distance of the displayed image.
For instance if an image captured by a Full Frame camera is viewed at ‘standard’ distance (that is a distance equal to its diagonal), it turns out that the portion of the MTF curve most representative of perceived sharpness appears to be around MTF90. On the other hand, when pixel peeping, the spatial frequencies around MTF50 look to be a decent, simple to calculate indicator of it with a current imaging system in good working conditions. Continue reading MTF50 and Perceived Sharpness