基于离散切比雪夫变换的图像接缝裁剪篡改检测

Image Seam Carving Tampering Detection by Discrete Tchebichef Transform

接缝裁剪(Seam Carving)作为近些年来热门的图像缩放技术之一,常被用于图像恶意篡改。当前对Seam Carving篡改的检测方法并不多,并均是针对JPEG格式图像,且在篡改比例较小时,检测准确率不高。文中方法利用离散切比雪夫变换后系数矩阵中的分布特点来提取特征以达到对图像接缝裁剪篡改的检测,并且该方法适用于多种图像格式,在小比例篡改的情况下依然保持较高的分类准确。利用离散切比雪夫变换(Discrete Tchebichef Transform,DTT)得到变换后的系数矩阵,提取Seam Carving篡改的痕迹,实现了对Seam Carving的篡改检测。所提方法首先将待检测图像分成8×8不重叠块,对每一个8×8块进行DTT变换,得到变换后的DTT系数矩阵;然后在每一块中分别计算DTT系数间的差异,再通过系数差异直方图得到统计矩阵,从统计矩阵中提取特征;最后使用支持向量机(Support Vector Machine,SVM)进行训练得到预测模型,实现对图像Seam Carving篡改的检测。实验结果表明,所提方法不仅适用于JPEG格式和TIFF格式的篡改图像,对小比例篡改也能达到较高的检测准确率。

As one of the most popular image scaling technologies in recent years,seam carving is often used for malicious tampering.We find that there are two shortcomings in the current research work of seam carving tamper detection.First,the detection methods are basically aimed at tampered JPEG image.For tampered TIFF image,the current detection methods have low accuracy.Second,when the ratio of seam carving tampering is small,the classification accuracy is relatively low.In order to solve these problems,this paper proposes a seam car-ving tamper detection method based on discrete Tchebichef transform.The tamper detection method is no longer limited to the image format,can effectively detect the tampered images of various formats,and maintain a high classification accuracy.In addition,when the tampering ratio is small,this method will not fail,and has a high classification accuracy.The method in this paper users the distribution characteristics of the coefficients in the coefficient matrix after the discrete Tchebichef transform to extract features to detect seam carved images.Moreover,this method is suitable for all kinds of image formats,and maintains a high classification accuracy under the condition of small tampering ratio.The proposed method makes use of the distribution characteristics of the coefficients in the coefficient matrix after discrete Tchebichef transform.After image segmentation and discrete Tchebichef transform,the value of the coefficient in the upper left corner of each block is very large,and the value in other positions is very small.The trace of seam carving is extracted and the tamper detection of seam carving is realized.Based on the characteristics of coefficient distribution in discrete Tchebichef transform coefficient matrix,the classification accuracy will not be affected by compression quality factor and will not change with the change of compression quality factor.The steps of this detection method are as follows.Firstly,the images are divided into 8×8 non-overlapping blocks,and then each block of the image is transformed by discrete Tchebichef transform to get the transformed coefficient matrix.Due to the characteristics of discrete Tchebichef transform,the coefficients of the upper left corner of each 8×8 block of the coefficient matrix are very large,and the coefficients of other positions are very small,so the differences between coefficients are calculated in each block of the coefficient matrix,and the histogram of the differences between coefficients is obtained.Finally,the statistical matrix is obtained from the histogram of the differences between the coefficients,and the features are extracted from the statistical matrix.The extracted features are sent to SVM for training,and a classification model is obtained.In this paper,a seam car-ving tamper detection method based on discrete Tchebichef transform is proposed to classify original images and tampered images.The experimental results show that this method can achieve high classification accuracy.The detection method based on discrete Tchebichef transform proposed in this paper can achieve high classification accuracy both in JPEG tampered image and TIFF tampered image,and also can achieve high detection accuracy for small-scale tampering.