MSRCR

Retinex is an image restoration approach used to restore the original appearance of an image. Among various methods, a center/surround retinex algorithm is favorable for parallelization because it uses the convolution operations with large-scale sizes to achieve dynamic range compression and color/lightness rendition. This paper presents a GPURetinex algorithm, which is a data parallel algorithm accelerating a modified center/surround retinex with GPGPU/CUDA. The GPURetinex algorithm exploits the massively parallel threading and heterogeneous memory hierarchy of a GPGPU to improve efficiency. Two challenging problems, irregular memory access and block size for data partition, are analyzed mathematically. The proposed mathematical models help optimally choose memory spaces and block sizes for maximal parallelization performance. The mathematical analyses are applied to three parallelization issues existing in the retinex problem: block-wise, pixel-wise, and serial operations. The experimental results conducted on GT200 GPU and CUDA 3.2 showed that the GPURetinex can gain 74 times acceleration, compared with an SSE-optimized single-threaded implementation on Core2 Duo for the images with 4,096 × 4,096 resolution. The proposed method also outperforms the parallel retinex implemented with the nVidia Performance Primitives library. Our experimental results indicate that careful design of memory access and multithreading patterns for CUDA devices should acquire great performance acceleration for real-time processing of image restoration.