Wagon-wheel ef­fectWagon-wheel效果

From从Michael’s迈克尔的 “Vi­su­alPhe­nom­ena & Op­ti­cal Il­lu­sionsVi­su­alPhe­nom­ena和视觉上的错觉”

What to什么ob­serve观察

When this page has loaded, the neigh­bor­ing demo is in “auto run” mode: the wheel ro­ta­tion smoothly varies be­tween stand­ing still and a max­i­mum speed of 120 ro­ta­tions per minute (120 rpm, in­di­cated at top right). 当本页面载入,邻近的演示,是在“自动运行”方式:车轮转动平稳而异呆呆地站在那里,一个最大速度为每分钟120旋转的转速,表明在120右上)。The wheel ro­ta­tion, how­ever, looks quite dif­fer­ent: it seems to slow down to stand­still when the max­i­mum speed of 120 rpm is in­di­cated! 车轮转动的,然而,看起来完全不同了。它似乎减速以静止不动时的最大速度每分钟转速显示120 !It helps to know that the wheel is ren­dered with stan­dard movie speed: 24 frames per sec­ond.这会让你知道,轮子被渲染速度与标准的电影:每秒24帧。

What to do要做什么

With the “thumbs” of the two ver­ti­cal slid­ers you can set the speed, the right slider is for coarse ad­just­ment. 以“拇指”的两个垂直的滑球,您可以设定速度,正确的滑球是为粗糙的调整。When you begin to ad­just the speed your­self, “auto run” switches off. 当你开始调整速度你自己,“自动运行”关上了。Now you can ob­serve that in­creas­ing the ro­ta­tion speed, start­ing from zero, in­deed ini­tially speeds up the wheel, but then it be­gins to slow down! 现在你可以观察到的旋转速度增加,从零开始,确实开始加速轮子,但是,然后它开始慢一点!Find the speed (≈120 rpm) where the spokes stand still (the left slider helps with fine ad­just­ment) – but ob­serve that the cen­tre, and cer­tain cute ir­reg­u­lar­i­ties around the wheel still move. 找到速度(rpm)在120≈辐条(左站立的滑球帮助与微调)——但当前研究已观察到,该中心,和一定的可爱的不规则周围旋转还是手动的。This tells you that the wheel still ro­tates, but be­cause of the sim­u­lated slow movie speed of 24 frames per sec­ond the spokes seem­ingly stand still, and can even go back­wards if you speed up! 这就告诉你,这个轮子仍然旋转,但由于在模拟的速度缓慢的电影每秒24帧辐条看似站着别动,甚至可以倒车如果你快点!There are ad­di­tional stand­stills at higher speeds, here you can check this around 240 rpm.还有其他的stand­stills在更高的速度,在这里你可以检查这个大概240每分钟转速。

This is what you may have ob­served in movies (es­pe­cially in West­erns with promi­nent spoked wagon wheels). 这是你可以观察到在电影中(尤其是在美国西部片具有突出的spoked马车车轮)。It should not occur in di­rect ob­ser­va­tion under steady day­light – though there is a lit­tle dis­cus­sion in that re­spect, some peo­ple re­port this ef­fect in day­light. 它不会出现在日光下稳定直接观察——尽管有一个小的讨论在这方面,一些人报告这个效果在日光下。Be­fore dis­cus­sion in­ter­ac­tion with “brain rhythms”, I have two ex­plana­tory sug­ges­tions:讨论互动以“大脑前节奏”,我有两个解释性的建议:

1. The light­ing is not re­ally steady, but some­what rhyth­mic, e.g. mod­u­lated by a fence with reg­u­lar gaps.灯光照明是不太稳定,但有些有节奏,例如调制由篱笆与常规的差距。
2. Roads, es­pe­cially when coated with con­crete, usu­ally have “tin­ing” (grooves cut into the con­crete sur­face a mm or so apart for trac­tion and in­creased grip when wet). 道路,特别是当上涂上一层混凝土,通常有“tin­ing”(沟槽切割混凝土表面一毫米左右分别为牵引和增加抓地力时,湿)。This tine tex­ture can lead to vi­bra­tion, which in com­bi­na­tion with cer­tain spoke shapes can cause the wagon whel ef­fect.该齿纹理可以导致振动,结合一定的形状会导致马车说话whel效果。

Com­ment评论

For this ef­fect to occur, the dis­play needs to be pre­sented dis­con­tin­u­ously – it may not be vis­i­ble, but the wheel (or any­thing in a movie or on TV for that mat­ter) moves in jerks. 因为这个效应发生,显示需要提出了间断——它根本不可能是可见的,但轮(或任何在电影或电视上为那件事)举措,在急速。If these jerks occur fast enough (e.g. around 20 times per sec­ond) our vi­sual sys­tem, namely its mo­tion de­part­ment, in­ter­po­lates the in­ter­ven­ing miss­ing po­si­tions.如果这些坏蛋发生足够快(例如大约20次/秒)我们的视觉系统,即它的运动部、in­ter­po­lates其间的失踪的位置。

This in­ter­po­la­tion re­lies on a “near­est neigh­bour”prin­ci­ple – thus, if the dis­place­ment of the wheel spoke from frame to frame is so large, that it is closer to the (for­mer) next spoke than to its (for­mer) orig­i­nal, our vi­sual sys­tem as­sumes that the op­po­site mo­tion di­rec­tion. 该插值依赖于一种“近邻”的原则,因此,如果位移量的车轮从外域框架,框架是如此之大,以致它是接近的(原)下说话比它的(前)原件,我们的视觉系统的假设相反的运动方向。This im­plies, of course, that the spokes are fully iden­ti­cal.这意味着,当然,辐条是完全相同的。

Sim­i­lar ef­fects occur with stro­bo­scopic light­ing (see next page), and in­deed this is used to mea­sure the speed of rapidly ro­tat­ing ma­chin­ery, for in­stance an air­plane pro­peller blade. 类似的作用发生于频闪照明(见下一页),事实上,这是用来测量快速旋转机械的速度,比如飞机螺旋桨桨叶。Tech­ni­cally, the en­tire ef­fect is a case of “alias­ing”.从技术上讲,整个效果是一例“别名”。

Sources来源

Wikipedia: Wagon-wheel ef­fect维基百科Wagon-wheel效果:

Cre­ated: 2007-July-132007-July-13造。