in my lecture notes about image sensors (CCD, precisely) I have read the following statement:
The transfer function $F(\omega)$ of the image sensor is related to its spatial resolution function $F(\omega)$: for the pixel scanning time $t_p =1/f_v$ (the pixel spaced by W and $f_v$ = video frequency) the scanning speed $v = \omega/t_p$ and the angular frequency $\omega$ (rad/s) are related to the spatial pulse $k$ (rad/ mm) of the pixel by the equation $v = ω/k$. So, the frame scanning frequency $f_q$ for N pixel frame is: $f_q = f_v/N$, where $N$ is the number of pixels. Then $F(ω) = F(kv) = MTF$ (Modulation transfer function).
Well, it seems quite obscure to me, and I have not found so much on the web about how to read it. Precisely, I have these doubts:
what does k represents? It is related to $1/W$, so I'd say it is the number of pixels per mm of length. But on the web I see it is sometimes expressed in line pairs per mm or cycles per pixel (but I do not understand these definitions in this situation).
what is the video frequency $f_v$? Why do we say "video" about an image?