What does frequency filtering actually practically mean?

1. What does it mean to filter a frequency?
2. What is the difference between practical and ideal filter?
3. What is the purpose of high-frequency filter?
4. What is the difference between spatial filtering and frequency filtering?

What does it mean to filter a frequency?

Frequency filters process an image in the frequency domain. The image is Fourier transformed, multiplied with the filter function and then re-transformed into the spatial domain. Attenuating high frequencies results in a smoother image in the spatial domain, attenuating low frequencies enhances the edges.

What is the difference between practical and ideal filter?

An ideal filter is considered to have a specified, nonzero magnitude for one or more bands of frequencies and is considered to have zero magnitude for one or more bands of frequencies. On the other hand, practical implementation constraints require that a filter be causal.

What is the purpose of high-frequency filter?

A high-pass filter is an EQ curve that is used to remove low-frequency sounds from an audio signal. It is called a high-pass filter because it allows high-frequency signals to pass through, while attenuating (reducing the amplitude of) lower-frequency signals.

What is the difference between spatial filtering and frequency filtering?

In spatial domain, we deal with images as it is. The value of the pixels of the image change with respect to scene. Whereas in frequency domain, we deal with the rate at which the pixel values are changing in spatial domain.