Low-Complexity Chroma Subsampling Using Optimal Lines of Subproblems of Pixel Distortion.

Video compression is an important procedure for digital applications. A commonly used format for inputs to video coders is YUV420, which is a subsampled result from YUV444, that is transformed and demosaicked from a color filter array (CFA) format. The process of chroma subsampling is a crucial step for the reconstructed image quality. A state-of-the-art method utilizes the solution of a prior method to compute the starting point, and devises a search method to improve the results. However, the search method does not consider the optimality condition of the problem, and the overall computational complexity is high because of the execution of the prior method for the starting point. In the proposed work, the cost function of the optimization problem is analyzed and decomposed into 4 subchannels based on the CFA format. The optimal line of each subterm is studied in 3-dimensional space. The problem is then mathematically reduced to a 3-subchannel problem. Based on the combinations of the optimal lines, a triangle search area is formed and proved to contain the optimal solution. And because the derived triangle search area is small on average, the search for the optimal value can be considerably fast. Experimental results demonstrate that the proposed approach can produce reconstructed images with qualities that are exactly the same as those generated using the state-of-the-art method. Relative to the state-of-the-art method, the proposed approach can reduce the time complexity by 84.08%–84.91%, and reduce the number of search points by 40.24%–85.25%, for the image datasets Kodak and IMAX with different demosaicking methods. [ABSTRACT FROM AUTHOR]