Publication: Developement of algorithim to reduce the shadow in digital image
Date
2012-06-01
Authors
Ong, Kok Tong
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Abstract
A shadow is usually appears in arbitrary shape. The shadow shape may or may not be the same as the shape of object casting it. The shadow shape depends on the incident angle of light source and the object casting it. Hence, it is difficult to recognize the shadow shape based on the object geometry. Other than that, the removal of shadow need to consider the original pixel intensity in the region that is previously covered by shadow. The original shadowed region may become too bright if the removal process of shadow is too aggressive or may be still dark if the removal process of shadow is not effective. Therefore, a new method of reducing shadow in digital image has been proposed in this project. Throughout the development of the new algorithm, a total of four shadow reduction algorithms have been implemented. The results from these four algorithms are compared with the same set of input images to make fair comparison. From hypothesis testing of Randomized Complete Block Design conclusion, it is shown that all implemented methods can change the pixel intensity of the image. The
performance of algorithms is further confirmed with the result of confident interval and main factor plot. It is found that the best algorithm is the one that calculates the scaling factor based on the mean and surrounding mean for shadow reduction. The proposed algorithm can detect the shadow implicitly and there is no need for user input to identify the shadow region explicitly. There are limitations that the proposed algorithm cannot detect shadow edge if the shadow penumbra region is narrow and the shadowed region cannot be on the boundary of image. However, the result shows that it can detect shadow with arbitrary shape correctly and reduce the shadow by scaling the pixel intensity back to background pixel intensity.