| Abstract: | A large number of manuscripts are found in various institutions, archives and other
museums and it is common for archive libraries to provide public access to
historical and ancient manuscript digital image collections to protect original hard
copies from damage and also to improve access. The Ethiopian National Archives
and Library Agency (ENALA) is in the process of digitizing its historical
manuscript collections and there is a need to ensure the quality of the digital images
of the manuscripts. This study is initiated with the objective of testing various
image noise filtering algorithms for their effect on enhancing digital images of
manuscripts under different conditions. Six historical manuscripts from the early
years of the 20th Century and two from each of manuscripts in good, medium and
poor conditions were purposely selected for this study. Images of each manuscript
were taken using digital cameras with 8 and 16 megapixel resolution. The images
were filtered using mean, median, Gaussian, morphological dilation and
morphological erosion algorithms with convolution kernel size of 3 by 3 and 5 by 5.
The PSNR, MSE and MAE are used as parameters of evaluation of the
effectiveness of the various filtering algorithms. The result has shown that similar
trend of the three parameters for all images and filtering algorithms. In addition
correlation values of higher than 0.87 were found for the parameters between
themselves. For the first set of image PSNR values of 21.64, 19.14, 16.78, 12.89
and 12.60 are obtained for the median, mean, Gaussian, morphological dilation and
Morphological erosion algorithms. Similar trend was observed for most of the other
images. No consistent effect of image resolution was observed but images of 8
megapixel have shown better quality after filtering images of manuscripts in good
and poor conditions, whereas images from manuscripts of medium condition with
16 megapixel has produced better images upon filtering. Kernel size at 3 by 3 was
found to be better than 5 by 5 for enhancing image quality. From the experimented
filtering algorithms, median filtering algorithm with 3 by 3 kernel size is proved
effective to improve the quality of images of historical manuscripts. Digital images
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taken at a minimum resolution of 8 megapixels appear to be adequate for images of
historical manuscripts. Evaluation of advanced image filtering techniques is
recommended for improving the quality of highly degraded manuscript images. |
