Coltuc Dinu, Datcu Mihai, Coltuc Daniela
Faculty of Electrical Engineering, Electronics and Information Technology, Valahia University of Targoviste, Târgoviște 130024, Romania.
Remote Sensing Technology Institute, German Aerospace Center (DLR), Germany and Research Centre for Spatial Information, Politehnica University of Bucharest, București 060042, Romania.
Entropy (Basel). 2018 Jan 31;20(2):99. doi: 10.3390/e20020099.
This paper investigates the usefulness of the normalized compression distance (NCD) for image similarity detection. Instead of the direct NCD between images, the paper considers the correlation between NCD based feature vectors extracted for each image. The vectors are derived by computing the NCD between the original image and sequences of translated (rotated) versions. Feature vectors for simple transforms (circular translations on horizontal, vertical, diagonal directions and rotations around image center) and several standard compressors are generated and tested in a very simple experiment of similarity detection between the original image and two filtered versions (median and moving average). The promising vector configurations (geometric transform, lossless compressor) are further tested for similarity detection on the 24 images of the Kodak set subject to some common image processing. While the direct computation of NCD fails to detect image similarity even in the case of simple median and moving average filtering in 3 × 3 windows, for certain transforms and compressors, the proposed approach appears to provide robustness at similarity detection against smoothing, lossy compression, contrast enhancement, noise addition and some robustness against geometrical transforms (scaling, cropping and rotation).
本文研究了归一化压缩距离（NCD）在图像相似性检测中的实用性。该论文并非考虑图像之间的直接NCD，而是研究为每个图像提取的基于NCD的特征向量之间的相关性。这些向量是通过计算原始图像与平移（旋转）版本序列之间的NCD得出的。针对简单变换（水平、垂直、对角线方向的循环平移以及绕图像中心的旋转）和几种标准压缩器生成特征向量，并在一个非常简单的原始图像与两个滤波版本（中值滤波和移动平均滤波）之间的相似性检测实验中进行测试。对于柯达图像集中经过一些常见图像处理的24幅图像，进一步测试了有前景的向量配置（几何变换、无损压缩器）用于相似性检测。虽然即使在3×3窗口中进行简单的中值滤波和移动平均滤波的情况下，直接计算NCD也无法检测到图像相似性，但对于某些变换和压缩器，所提出的方法在相似性检测中似乎对平滑处理、有损压缩、对比度增强、噪声添加具有鲁棒性，并且对几何变换（缩放、裁剪和旋转）也具有一定的鲁棒性。
