提出了一种针对经过JPEG (joint photographic experts group, 联合图像专家小组) 压缩但保存为bmp 或tiff格式图像的质量因子检测新方法. 通过统计待测图像灰度直方图, 获取最大值所对应的指定灰度级. 然后将待测图像进行8×8 分块, 统计每个8×8 小块中指定灰度级所对应的位置直方图. 最后将所有块对应的位置直方图累加,作为待测图像中指定灰度级的位置直方图, 根据压缩前后的位置直方图差异估计质量因子. 实验结果表明, 本方法可以有效地检测图像质量因子且正确率较高. 最后, 分析了单次高质量因子压缩图像的相似度曲线在高质量因子处的导数特点, 并提出了改进方案. 实验结果表明, 改进方案较大地提高了高质量因子的检测正确率.
This paper proposes a new method for estimation of JPEG (joint photographic experts group) quality factor for images once compressed but saved in the bmp or tiff format. By calculating a gray histogram of the test image, the gray value was set at the maximum of the gray histogram occurs. The test image is split into 8×8 blocks, and a position histogram of the specified gray value g in each 8×8 block is obtained. The position histograms of all blocks are combined to produce a position histogram of the entire image, from which the quality factor of the test image is estimated. Experiments show that the method has a high correct rate. In addition, derivative characteristics of similarity curves of images having undergone single JPEG compression with high quality are analyzed at some high quality factors, and an improved version of a previous method is proposed, and verified in experiments.
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