1997 年 17 巻 4 号 p. 211-221
It is known that the Wiener spectrum obtained by one dimension scanning method depends on both the slit length of scanning aperture and the modulation transfer function (MTF) of radiographic screen-film system. Although the former has been studied and made clear by many authors, no previous work of the latter has been done. The dependence of the measured Wiener spectrum on MTF was investigated theoretically and experimentally. As the result of present work, it appears that the measured Wiener spectrum at low frequencies is under-estimated and the amount of the under-estimation increases as the resolution of the system becomes lower and its behavior can be explained by the increase of the slit length of scanning aperture necessary for accurate measurement. If physical image qualities of the systems with different MTFs are calculated by using the under-estimated Wiener spectrum, they may lead to wrong results. It is shown that comparisons between the systems must be done by using image qualities estimated by proper physical image quantities.