[Paper] Color Reproduction of Glass Dry Plate Scanned by a Linear Sensor Camera Using Filter Coefficient

Abstract

Cultural heritage objects are threatened with the destruction caused by decay or damage due to aging, unpredictable natural and man-made disaster such as fire, earthquake, and war. Deterioration or disappearance of any cultural or natural heritage constitutes a great loss to all nations of the world. Due to the precious nature of cultural heritage, it is necessary to choose a proper solution for their preservation and conservation. There are various methods nowadays that can record different information of cultural heritage, such as color, shape, spectral reflectance, etc. Such recording methods also refer to digital archiving which has been gathering increasing interests of researchers in the past few years1, 2). The motivation is to ensure that future generations could inherit and admire these amazing works. A variety of technologies have been applied to the preservation of cultural heritage. Photography is one of the leading techniques which provides a new frontier to the field of archiving. However, due to the limitation of the technique development in the old days, some of the archiving results cannot satisfy all the demands, especially in some exceptional scenarios. For an instance, Horyuji Kondo wall painting, which belongs to UNESCO World Heritage Site under the name Buddhist Monuments in the Horyuji Area, was photographed onto a one-to-one scale glass dry plate with multiband filters (Appearance color: Yellow, Red, Green, Blue) 85 years ago (1935) 3). These glass-based dry plates are the only documentation material that recorded the original appearance of the wall painting during that time, but the coating layer is now fragile and sensitive to storage conditions4). A calamitous fire that broke out later in 1949 which resulted in the severe damage to the wall paintings5). Fortunately, the color image of the wall painting can be reproduced using the glass dry plates by a traditional technique with the negative-positive process. However, this reproducing process that is known as collotype printing6), reproduces the color by a trained craftsman using the glass dry plates manually. The only evaluation criteria for the reproduction is the experience of the craftsman. This is very subjective. Area sensor-based imaging system is widely used in the digital archiving nowadays. This technique can accomplish the image acquisition work easily and efficiently. Such imaging system offers fairly uniform light distribution, relatively high resolution and relatively accurate color rendering7). However, if an area sensor-based imaging system and a linear sensor-based imaging system are compared under an identical imaging setup condition including the same theoretical imaging resolution, the light source, etc., it has some Abstract A method for color reproduction of old glass dry plates digitized by a linear sensor camera is proposed. A high-resolution scanner based on linear sensor camera was developed for digitizing glass plates, which is beneficial for high-quality color reproduction. The color reproduction uses filter coefficient calculated from color information of multiband filters. An approach for the calculation of filter coefficient used for color reproduction is addressed in detail. The method was applied to the digitization and color reproduction of a wall painting belonging to World Cultural Heritage Horyuji Kondo, Japan. A verification experiment is conducted to evaluate the accuracy of color reproduction results. Experimental results show that the proposed method is capable of high-quality color reproduction of image details, and there is merit to using this high-resolution digitization techniques for cultural heritage.