Improved illumination invariant homomorphic filtering using the dual tree complex wavelet transform
Paul Hill, Harish Bhaskar, Mohammed Ebrahim Al-Mualla, David Bull · 2016
A novel adaptation of the two dimensional Homomorphic filter is introduced using the Dual Tree Complex Wavelet Transform for improved illumination invariant processing. The Homomorphic filter is conventionally implemented within the log-Fourier domain using an isotropic high-pass filter based on the assumption that the illumination signal occupies low spatial frequencies. In this case however, low frequency structural reflectance content will be incorrectly attenuated. Our method implements the Homomorphic filter using the DT-CWT and exploits the property of cross scale persistence (for structural content) to generate a filter that retains cross scale content and therefore reduces incorrect attenuation of structural reflectance content.