# Spatial frequency and video frequency of an image

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?

• That seems very unclear, indeed. Perhaps dig earlier in your notes? In particular, it seems to bounce back and forth between spatial resolution and temporal resolution -- or when they say "scanning time $t_p$" they mean some spatial thing. Could they be talking about a line scanner? Jul 15, 2020 at 19:20
• I think that scanning may mean transmitting charge between two consecutive pixels and storing data sequentially in a line Jul 15, 2020 at 19:40