针对现有JPEG图像压缩与增强的过程分离,且图像增强后容易产生块状效应的局限性,提出一种新的JPEG图像增强算法,该算法嵌入JPEG图像压缩框架之中,在量化步骤之前增强图像以充分利用图像原始信息。增强过程以Retinex理论为基础,将DCT系数分为照度分量(DC系数)和反射分量(AC系数),对DC系数进行动态范围调整,并利用DC系数的增强因子对AC系数做细节增强。最后,对调整后的DCT系数做平滑处理来抑制块效应。实验结果表明,与传统的其他算法相比,该算法能更好的增强细节信息和保持色彩信息,并能保持与标准JPEG同等的图像压缩比。

A new JPEG image enhancement method based on Retinex theory is proposed to improve the existing enhancement methods. The exiting methods cannot enhance images effectively because after JPEG compression images will lose some information. The proposed algorithm enhances images before quantization in the JPEG compression process to use full primal information of images. The discrete cosine transform (DCT) coefficients are divided into the incident component (DC coefficients) and the reflection component (AC coefficients) based on the Retinex theory; the DC coefficients are adjusted in the image dynamic range, and the AC coefficients are adjusted to enhance the details with the enhancement factors of the DC coefficients. The block artifacts will be suppressed by smoothing the DCT coefficients. Compared to other enhancement algorithms, results show the new approach’s efficiency in details enhancement and color preserving, while keeping the same compression ratio as the normal JPEG compression.