add MTF | Strolls with my Dog

In this and the previous article I discuss how Modulation Transfer Functions (MTF) obtained from every raw color plane of a Bayer CFA in isolation can be combined to provide an objective and meaningful composite MTF curve for the imaging system as a whole. There are two main ways to accomplish this goal:

an input-referred linear Hardware System MTF ( $MTF_L$ ) that reflects the mix of spectral information captured in the raw data, divorced from downstream color science; and
an output-referred linear Luminance System MTF ( $MTF_Y$ ) that reflects the luminance channel of the image as neutrally displayed.

Both are valid on their own, though the weights of the former are fixed for any Bayer sensor while the latter are scene, camera/lens and illuminant dependent. For this reason I usually prefer input-referred weights as a first pass when comparing cameras and lens hardware in similar conditions. Continue reading System MTF from Bayer Sensors →

For the purposes of ‘sharpness’ spatial resolution measurement in photography cameras can be considered shift-invariant, linear systems when capturing scene detail of random size and direction such as one often finds in landscapes.

Shift invariant means that the imaging system should respond exactly the same way no matter where light from the scene falls on the sensing medium . We know that in a strict sense this is not true because for instance pixels tend to have squarish active areas so their response cannot be isotropic by definition. However when using the slanted edge method of linear spatial resolution measurement we can effectively make it shift invariant by careful preparation of the testing setup. For example the edges should be slanted no more than this and no less than that. Continue reading Linearity in the Frequency Domain →

Musings about Photography