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New Nonphotorealistic Shading Algorithm to Improve the Perceptual Quality of Two-Dimensional Images

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We propose a nonphotorealistic shading algorithm to improve the perceptual quality of two-dimensional natural images that do not have depth information. Shading plays an important role in the human perception of three-dimensional shapes; however, an appropriate normal is indispensable to the shading approach. Generally, it is pointed out that luminance variation due to shading is useful as an indicator of shape and that the depth values are strongly related to the luminance distribution of the object. Therefore, first, we compute the surface normals from the variation in the luminance at each pixel. Second, we enhance the shade by controlling the azimuth of the normals on the basis of the angle between each normal and a given light source direction. From experimental results of the natural images and subjective test, we demonstrate that the three-dimensional (3D) appearance can be improved by our shading approach. Moreover, we also propose an advanced shading approach, which is the combination of our shading approach and the process of selecting the suitable light direction, and we show the performance of selecting the suitable light direction and also demonstrate that the 3D appearance can be more enhanced by using the suitable light direction. Last, we investigate the possibilities of the advanced shading approach.

Document Type: Research Article


Affiliations: 1: Faculty of Computer and Information Sciences, Sojo University, 4-22-1 Ikeda, Kumamoto City, Kumamoto 860-0082, Japan 2: Digital & Network Technology Development Center, Panasonic Corporation, 1006 Kadoma, Kadoma City, Osaka 571-8501, Japan

Publication date: 2009-09-01

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  • The Journal of Imaging Science and Technology (JIST) is dedicated to the advancement of imaging science knowledge, the practical applications of such knowledge, and how imaging science relates to other fields of study. The pages of this journal are open to reports of new theoretical or experimental results, and to comprehensive reviews. Only original manuscripts that have not been previously published, nor currently submitted for publication elsewhere, should be submitted.

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