ディジタルカメラにおけるJPEG非可逆圧縮の定量的特性評価

摘要

一般向けディジタルカメラの画素数の増大は，その 速度が鈍ってきた感はあるが，まだ止まってはいない ようである。2007年11月現在，1，200万画素のコンパク トディジタルカメラが4万円でも入手可能となってお り，さらに，レンズ交換式一眼レフディジタルカメラ では，11月未に2，100万画素を超える機種の発売も予定 されている。%The recent increase in number of pixels of images acquired by a digital camera encourages one to utilize it for image measurement. A large number of pixels of the image bring difficulties in dealing with it. Therefore, lossy image compression is going to be required. Almost all digital cameras have the built-in function of lossy JPEG compression. Since there are few reports on evaluation of image matching accuracy using a pair of lossy compressed images acquired by a digital camera, we decided to investigate effects of lossy JPEG compression executed in a digital camera on the accuracy of image matching. This paper reports the preparatory experiment conducted in order to evaluate lossy JPEG compression quantitatively by using 54 diverse images. Two compression parameter sets of a downsampling ratio, a quantization table, and a Huffman code table utilized in Canon EOS 20D were investigated. The experiment results demonstrate that the compression ratio is correlated to grey level difference vector measures. Furthermore, the experiment results suggest that the degradation of quality of images reconstructed from images compressed in a digital camera is so small that it may have no effect on the accuracy of image matching.