Signals and systems are not limited to one-dimensional functions of the independent variable time. This lesson introduces you to signals that are a function of a two discrete-valued space variables. We often call such signals "images". You will learn about the point-spread function, which is the two-dimensional analog of the impulse response for a one-dimensional system. You will also learn how to perform convolution of a two-dimensional signal with a point-spread function. These concepts provide a glimpse into the field of image processing and prepare you to extend the concepts you are learning to three and higher dimensional signals.