A camera might produce a pixel by computing the average light input over a square, and in that sense you could consider the pixel itself a square.
But in signal processing you interpret it as a two step procedure: First, for every mathematical point of the scene, compute the average light input of the surrounding square to produce a band limited signal. Second, for every pixel report the value at the corresponding point in the band limited image.
The first step is filtering (in this case with a box filter), the second is point sampling.
But in signal processing you interpret it as a two step procedure: First, for every mathematical point of the scene, compute the average light input of the surrounding square to produce a band limited signal. Second, for every pixel report the value at the corresponding point in the band limited image.
The first step is filtering (in this case with a box filter), the second is point sampling.