The rotating grid illusion


	The rotating grid illusion

rj3sp

10-10-2008 11:51 AM

382 views

tags:

optical, stroboscopic, grid, temporal aliasing

rj3sp says:

A surprising optical illusion which is related to temporal aliasing, a visual phenomenon also known as the stroboscopic effect, which accounts for the fact that in video or motion pictures, wheels sometimes appear to be turning backwards.

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<div style="margin: 12px 0px; font-family: arial; color: #333333; background: #ffffff; border: solid 4px #e5e5e5; width: 100%; clear: left;"><div class="CM_CTB_Content_Wrap" style="margin: 0px; padding: 0px;background-color: #ffffff;"><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content.clipmarks.com/blog_embed/4a662dff-1545-4417-92a3-fb3f6c862549/B79FF33B-51FD-410F-8A7B-E4C636A87673/" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://blog.ted.com/2008/09/rotating_grid_i_1.php" href="http://blog.ted.com/2008/09/rotating_grid_i_1.php" style="font-size: 11px;">blog.ted.com</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://blog.ted.com/2008/09/rotating_grid_i_1.php"><div align="center"><img src="http://content6.clipmarks.com/blog_cache/blog.ted.com/img/9EFEB630-BFAA-4717-BA57-053314FCA325" alt="" /></div></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://blog.ted.com/2008/09/rotating_grid_i_1.php"><P>Filmmaker and animator <A href="http://www.davidoreilly.com/">David O'Reilly</A> (who came up with the concept for <A href="http://gizmodo.com/5040631/3d-app-converts-iphone-into-window-to-alternative-world">iHologram</A>) has noticed an interesting property in this animated GIF:</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://blog.ted.com/2008/09/rotating_grid_i_1.php"><div align="center"><img src="http://content7.clipmarks.com/blog_cache/blog.ted.com/img/8E16A222-1F42-49A0-AD68-6048868A1BC9" alt="dor_grid_300x300.gif" /></div></blockquote><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content8.clipmarks.com/images/clip-icon.gif" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://www.davidoreilly.com/2008/07/rotating-grid-illusion" href="http://www.davidoreilly.com/2008/07/rotating-grid-illusion" style="font-size: 11px;">www.davidoreilly.com</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.davidoreilly.com/2008/07/rotating-grid-illusion"><DIV id="masthead">
<DIV id="blogName"> <A href="http://www.davidoreilly.com/">David OReilly</A> </DIV>
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</DIV></DIV></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.davidoreilly.com/2008/07/rotating-grid-illusion"><P>A large grid seen rotating at a certain speed will appear to group itself into smaller grids, spinning independently.</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.davidoreilly.com/2008/07/rotating-grid-illusion"><div align="center"><img src="http://content9.clipmarks.com/blog_cache/www.davidoreilly.com/img/5492A42F-CB3F-4B35-B68A-9F06E3B37AF1" alt="" /></div></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.davidoreilly.com/2008/07/rotating-grid-illusion">explaination</blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.davidoreilly.com/2008/07/rotating-grid-illusion"><P>You are trying to capture a motion that is too fast for the framerate you’re using. In the case of a spinning wheel, what happens is that the wheel might turn, for example, 350 degrees between two frames but your eyes interpret it as -10 degrees. A similar thing happens with your grid. At the periphery, the lines move by more than one grid cell between two frames and the resulting visible motion is “snapped” to the smallest possible motion. The correct way to prevent such artifacts is to make sure that the shutter of the camera is open during the full interval between two frames, so that motion that is too fast gets blurred.</P></blockquote><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content6.clipmarks.com/images/clip-icon.gif" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://en.wikipedia.org/w/index.php?title=Temporal_aliasing&oldid=235345082" href="http://en.wikipedia.org/w/index.php?title=Temporal_aliasing&oldid=235345082" style="font-size: 11px;">en.wikipedia.org</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://en.wikipedia.org/w/index.php?title=Temporal_aliasing&oldid=235345082"><SPAN>Temporal aliasing</SPAN></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://en.wikipedia.org/w/index.php?title=Temporal_aliasing&oldid=235345082"><div align="center"><img src="http://content7.clipmarks.com/blog_cache/en.wikipedia.org/img/B9420FFC-BA2C-4D8C-A357-4008D32BBE30" alt="If the flash is synchronized with the motion the element appears motionless" /></div></blockquote></div><div style="margin: 0px 6px 6px 4px;"><table style="font-size: 11px;border-spacing: 0px;padding: 0px;" cellpadding="0" cellspacing="0" width="100%"><tr><td style="background:transparent;border-width:0px;padding:0px;">&nbsp;</td><td align="right" style="background:transparent;border-width:0px;padding:0px;width:107px" width="107"><a href="http://clipmarks.com/share/B79FF33B-51FD-410F-8A7B-E4C636A87673/blog/" title="blog or email this clip"><img src="http://content8.clipmarks.com/images/c2b-foot.png" border="0" alt="blog it" width="107" height="17" style="border-width:0px;padding:0px;margin:0px;" /></a></td></tr></table></div></div>

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