Contrast enhancement for mailpiece images

The authors present techniques for improving the contrast in spectrally variant images of mailpieces. These techniques were investigated for a system that captures mailpiece images and performs address interpretation in real-time. Hence it was necessary to satisfy both time constraint and an enhancement criterion. The methods developed are fast and are suitable for real-time applications. The large spectral variation of mailpiece images results in images of low-contrast. Examples are images of dark-colored envelopes with dark ink, such as greeting card envelopes, specially-designed envelopes and so on. This necessitates contrast enhancement methods to be highly adaptive. In the algorithms described most of the parameters are estimated dynamically from image characteristics. Conventional contrast enhancement methods are designed for a static environment and not amenable for use within this problem domain. Their method improves on previous work described by DuVall (1979) in compensating for the limited spectral response of the imaging system