attenuate the illunimation (low frequency) and increase the reflectance (high frequency)
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Given the fact that homomorphic filtering can be used to split low-frequency illumination and high frequency reflectance from an image, an obvious use of this is in change detection. In change detection, when we compare two images we look for changes in high frequency reflectance part. If we filter away the low frequency illumination part away, that helps.
After homomorphic filtering, the bright input image on the left yields the one on the right.