What is f(x,y) in Digital Image Processing? I am a novice in Digital Image Processing, and while reading the book of DIP by Gonzalez and Woods, I find that they have represented digital image as $f(x,y)$ but nowhere it is mentioned what is $x$ and $y$ actually that we are passing to the function $f?$ Does $f(x,y)$ represent the intensity of the points located at point $(x,y)$, so does $f$ actually returns the intensity of the pixel at that point or is it something else that I am missing?
Yes, it represent the intensity at that point.

f( x, y ) gives the intensity of a channel at position (x, y) 


Source : https://courses.cs.washington.edu/courses/cse557/00wi/lectures/imageprocessing.pdf