The Fourier series is an effective tool for representing periodic functions like a train of square waves. Consider a pulse-train waveform consisting of a sequence of rectangular pulses. If the period of these pulses is finite, the waveforms can be represented by a Fourier series. Now, if the period of the pulse-train increases, the frequency of the obtained line spectra decreases. But what if the period goes to infinity, resulting in a single pulse? In this case, the summation in the Fourier series evolves into a continuous integral, known as the Fourier transform. According to Dirichlet conditions, a periodic function can be expanded in terms of sinusoids if it has a finite number of discontinuities, maxima, and minima and is integrable. If a function fails these conditions, it cannot be represented by a Fourier series. Fourier transform is commonly used in image processing, where it helps enhance images and filter out noise, making the details clearer and sharper.