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Mathematical Equations for Homomorphic Filtering in Frequency Domain: A Literature Survey

Homomorphic filtering technique is one of the important ways used for digital image enhancement, especially when the input image is suffers from poor illumination conditions. This filtering technique has been used in many different imaging applications, including biometric, medical, and robotic vision. Homomorphic filtering works in frequency domain, by applying a high-pass type filter to reduce the significance of low frequency components. However, in literatures, there are several versions of mathematical equation used to present this filter. Therefore, this paper will review some of these equations.