目的 图像篡改检测主要分为图像区域复制篡改、图像拼接和对象移除3个方向，其中图像复制粘贴篡改是图像篡改检测的重要研究方向之一。针对目前大多数复制粘贴篡改检测方法难以检测平滑和小的篡改区域，且虚警率较高等问题，提出了一种基于匹配对的密度聚类MP-DBSCAN(matched pairs——density based spatial cluster-ing of applications with noise)和点密度过滤策略的图像复制粘贴篡改检测方法。方法 首先，在图像中提取大量关键点，根据关键点的灰度值分组后进行匹配。其次，提出了一种改进的密度聚类算法MP-DBSCAN，聚类对象为匹配对的一侧，并利用匹配对的另一侧约束聚类过程，即使篡改区域在空间上距离较近，或者篡改区域存在多个的情况，也能把不同的篡改区域较好地区分开来。此外，本文还提出了一种点密度过滤策略，通过删除低密度簇，降低了检测结果的虚警率。最后，通过估计仿射矩阵并使用ZNCC(zero-mean normalized cross-correlation)算法定位篡改区域。结果 消融实验表明了MP-DBSCAN算法和点密度过滤策略的有效性。在FAU、MICC-F600、GRIP和CASIAv2。0这4个数据集上与几个经典的和新颖的检测方法进行了对比实验，本文方法的F1在4个数据集上像素层的实验结果分别是0。914 3、0。890 6、0。939 1和0。856 8。结论 本文提出的MP-DBSCAN聚类算法和点密度过滤策略能有效提高检测算法的性能，即使篡改区域经过旋转、缩放、压缩和添加噪声等处理，本文方法依然能够检测出大部分的篡改区域，性能优于当前的检测算法。
Image copy-move forgery detection based on the clustering of matched pairs
Objective In recent years,with the development of the internet and computer technology,manipulating images and changing their content have become trivial tasks.Therefore,robust image tampering detection methods need to be developed.As passive forensic methods,image forgery methods can be categorized into copy-move,splicing,and inpaint-ing methods.Copy-move involves copying part of the original image to another part of the same image.Many excellent copy-move forgery detection(CMFD)methods have been developed in recent years and can be categorized into block-based,keypoint-based,and deep learning methods.However,these methods have the following drawbacks:1)they cannot easily detect small or smooth tampered regions;2)a massive number of features leads to a high computational cost;and 3)false alarm rates are high when the tampered images involve self-similar regions.To solve these issues,a novel CMFD method based on matched pairs,namely,density-based spatial clustering of applications with noise(MP-DBSCAN),is proposed in this paper along with point density filtering.Method First,a large number of scale-invariant feature transform(SIFT)keypoints are extracted from the input image by lowering the contrast threshold and normalizing the image scale,thus allow-ing the detection of a sufficient number of keypoints in small and smooth regions.Second,the generalized two nearest neighbor(G2NN)matching strategy is employed to manage multiple keypoint matching,thus allowing the detection algo-rithm to perform smoothly even when the tampered region has been copied multiple times.A hierarchical matching strategy is then adopted to solve keypoint matching problems involving a massive number of keypoints.To accelerate the matching process,keypoints are initially grouped by their grayscale values,and then the G2NN matching strategy is applied to each group instead of the keypoints detected from the entire image.The efficiency and accuracy of the matching procedure can be improved without deleting the correct matched pairs.Third,an improved clustering algorithm called MP-DBSCAN is proposed.The matched pairs are grouped into different tampered regions,and the direction of the matched pairs are adjusted before the clustering process.The cluster objects only represent one side of the matched pairs and not all the extracted keypoints,and the keypoints from the other side are used as constraints in the clustering process.A satisfying detection result is obtained even when the tampered regions are close to one another.The proposed method obtains better F,measures compared with the state-of-the-art copy-move forgery detection methods.Fourth,the prior regions are con-structed based on the clustering results.These prior regions can be regarded as the approximate tampered regions.A point density filtering policy is also proposed,where each point density of the region is calculated and the region with the lowest point density is deleted to reduce the false alarm rate.Finally,the tampered regions are located accurately using the affine transforms and the zero-mean normalized cross-correlation(ZNCC)algorithm.Result The proposed method is compared with the state-of-the-art CMFD methods on four standard datasets,including FAU,MICC-F600,GRIP,and CASIA v2.0.Provided by Christlein,the FAU dataset has an average resolution of about 3 000 × 2 300 pixels and includes tampered images under post-processing operations(e.g.,additional noise and JPEG compression)and various geometrical attacks(e.g.,scaling and rotation).This dataset involves 48,480,384,432,and 240 plain copy-move,scaling,rotation,JPEG,and noise addition operations,respectively.The MICC-F600 dataset includes images in which a region is dupli-cated at least once.The resolutions of these images range from 800 × 533 to 3 888 × 2 592 pixels.Among the 600 images in this dataset,440 are original images and 160 are forged images.The GRIP dataset includes 80 original images and 80 tampered images with a low resolution of 1 024 × 768 pixels.Some tampered regions on these images are very smooth or small.The size of the tampered regions ranges from about 4 000 to 50 000 pixels.The CASIA v2.0 dataset contains 7 491 authentic and 5 123 forged images,of which 1313 images are forged using copy-move methods.Precision,recall,and F,scores are used as assessment criteria in the experiments.The F,scores of the proposed method on the FAU,MICC-F600,GRIP,and CASIA v2.0 datasets at the pixel level are 0.914 3,0.890 6,0.939 1,and 0.856 8,respectively.Extensive experimental results demonstrate the superior performance of the proposed method compared with the existing state-of-the-art methods.The effectiveness of the MP-DBSCAN algorithm and the point density filtering policy is also demonstrated via ablation studies.Conclusion To detect tampered regions accurately,a novel CMFD method based on the MP-DBSCAN algorithm and the point density filtering policy is proposed in this paper.The matched pairs of an image can be divided into different tampered regions by using the MP-DBSCAN algorithm to detect these regions accurately.The mismatched pairs are then discarded by the point density filtering policy to reduce false alarm rates.Extensive experimental results demon-strate that the proposed method exhibits a satisfactory accuracy and robustness compared with the existing state-of-the-art methods.
multimedia forensicsimage forensicsimage forgery detectioncopy-move forgerydensity based spatial clustering of applications with noise(DBSCAN)
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