关键词: 图像放大, 各向异性四阶偏微分方程, 总变差, 冲激滤波器

Abstract:

To enhance the weak edges and textures and to avoid the staircase effect, an image enlargement method was proposed which coupled anisotropic forth-order partial differential equation to second-order partial differential equation. In the method, the weak edges and textures were enhanced and staircase was reduced by improved anisotropic forth-order partial differential equation with adaptive diffusion coefficient to threshold value constrained by pixel's local variance, improved total variance and adaptive amplitude shock filters controlled by gradient were coupled with the forth-order differential equation to enhance the edges, and the bi-orthogonal projection was used to realize the constraint of the degradation model. Simulation experiment results validate the proposed method on enhancing the edges, details and textures and reducing staircases. Compared with other existing second-order PDE-based zoom methods, the zoomed images using the proposed method have better visual effect and higher Peak Signal-to-Noise Ratio (PSNR) and Mean Structural Similarity Measure (MSSIM), for example, PSNR of zoomed image with larger smooth part by the proposed method is about 0.1 dB higher than that by improved Total Variance (TV) enlargement method and PSNR of zoomed image with larger weak edges and textures by the proposed method is above 0.5 dB higher than that by improved TV enlargement method. Therefore, the zoomed image of the method looks more natural, and the resolution of the weak edges and textures of the image are enhanced better.

Key words: image enlargement, anisotropic forth-order partial differential equation, Total Variance (TV), shock filter