Savoy R L, McCann J J
J Opt Soc Am. 1975 Mar;65(3):343-50. doi: 10.1364/josa.65.000343.
The number of cycles in a low-frequency sinusoidal display is a crucial variable in determining the visibility of the display. In particular, the threshold contrast is essentially independent of spatial frequency for these displays. We have extended the above experiments, using more cycles and a variety of targets and observer tasks. The results confirm previous findings; they also show that the type of target or task has little influence. For low-frequency sinusoids that contain up to about 3 cycles, the threshold contrast is determined by the number of cycles. For high-number-of-cycles targets with spatial frequencies above 6-10 cycles per degree, visibility is predominantly dependent on the spatial frequency. The results suggest that the low-frequency decrease in reported MTF's is due to the decrease of the number of cycles used in determining them.
低频正弦显示中的周期数是决定显示可见性的一个关键变量。特别是，这些显示的阈值对比度基本上与空间频率无关。我们扩展了上述实验，使用了更多的周期以及各种目标和观察者任务。结果证实了先前的发现；它们还表明目标或任务的类型影响很小。对于包含多达约3个周期的低频正弦波，阈值对比度由周期数决定。对于每度空间频率高于6 - 10个周期的高周期数目标，可见性主要取决于空间频率。结果表明，报告的调制传递函数（MTF）在低频时的下降是由于确定它们时所使用的周期数减少所致。
