Watanabe Haruyuki, Tsai Du-Yih, Lee Yongbum, Nakamura Tomohiro, Miyazaki Masanori, Kuramochi Yoshio, Kojima Katsuyuki
Department of Radiological Technology, Teikyo University Chiba Medical Center.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2009 Dec 20;65(12):1618-27. doi: 10.6009/jjrt.65.1618.
Joint photographic experts group(JPEG)and JPEG2000 are widely used as image compression algorithms in medical image database systems. Compressed images have been mainly evaluated by visual assessment on acceptable compression levels in clinical studies. However, to the best of our knowledge, little work has been done to clarify image properties based on physical analysis. In this work, investigations were made to clarify image properties based on physical analysis and to discuss the major causes of degradation related to compression ratios. The physical properties of JPEG2000-compressed and JPEG-compressed images in computed radiography(CR)were compared by measuring the characteristic curve, modulation transfer function(MTF), noise power spectrum(NPS), peak signal-to-noise ratio(PSNR), contrast-to-noise ratio(CNR), and noise equivalent quanta(NEQ). In the MTF measurement, the MTFs of JPEG at high compression ratio showed pronounced degradation at all frequencies. The NPS values of JPEG2000 tend to decrease considerably compared to that of the JPEG at all frequencies with the increase of compression ratio. Furthermore, JPEG2000 images showed higher PSNR, CNR, and NEQ values than JPEG images in the same compression ratio. In these signal-to-noise ratio measurements, good reproducibility of JPEG2000 images was achieved. Overall, JPEG2000 compressed images were far superior to JPEG compressed images. In the physical properties measured, these physical analyses are useful to comprehend physical properties for each irreversible compressed image related to compression ratios in CR.
联合图像专家组（JPEG）和JPEG2000作为图像压缩算法在医学图像数据库系统中被广泛使用。在临床研究中，压缩图像主要通过视觉评估来评价其可接受的压缩水平。然而，据我们所知，基于物理分析来阐明图像特性的工作做得很少。在这项工作中，我们进行了研究，以基于物理分析来阐明图像特性，并讨论与压缩比相关的图像质量下降的主要原因。通过测量特性曲线、调制传递函数（MTF）、噪声功率谱（NPS）、峰值信噪比（PSNR）、对比度噪声比（CNR）和噪声等效量子（NEQ），比较了计算机X线摄影（CR）中JPEG2000压缩图像和JPEG压缩图像的物理特性。在MTF测量中，高压缩比下JPEG的MTF在所有频率上均表现出明显下降。随着压缩比的增加，在所有频率上JPEG2000的NPS值与JPEG相比有相当大的下降趋势。此外，在相同压缩比下，JPEG2000图像的PSNR、CNR和NEQ值高于JPEG图像。在这些信噪比测量中，JPEG2000图像具有良好的重现性。总体而言，JPEG2000压缩图像远优于JPEG压缩图像。在所测量的物理特性方面，这些物理分析有助于理解CR中与压缩比相关的每个不可逆压缩图像的物理特性。
