In the "Digital Image Processing: Principles and Applications" book, it mentions the following relating to "Spatial frequence":
All images contain details, some fine details and some coarse details. These details are made up of brightness transitions that cycle from dark to light and back to dark. The rate at which brightness cycle is the spatial frequency . The higher the cycle rate, the higher the spatial frequency.
Can you explain this paragraph especially "Cycle rate"? And, if there is an example, this will be much helpful.