Which of the following is classified as a high pass filter?

A ramp filter is classified as a high pass filter because it enhances the high-frequency components of a signal while attenuating the low-frequency components. This characteristic is crucial in imaging techniques such as computed tomography (CT), where it is used in the reconstruction process to sharpen edges and improve image resolution. The ramp filter effectively boosts the high-frequency data corresponding to fine details in the image, allowing for clearer visualization of structures.

In contrast, the Hanning, Parzen, and Butterworth filters are primarily used for smoothing or reducing high-frequency noise in data. The Hanning filter, for instance, is a window function that mitigates spectral leakage but does not function as a high pass filter. The Parzen filter, which is used for kernel density estimation, also focuses on smoothing. The Butterworth filter, known for its smooth frequency response, typically serves as a low-pass filter, effectively allowing low frequencies to pass while dampening higher frequencies. These other filters therefore serve different purposes in signal processing compared to the ramp filter's high-pass functionality.