Cockatoo coming through

One of my favourite René Magritte paintings is Carte Blanche. (There seem to be problems linking to an image of that – I guess copyright related – but just put that title into an image search).  I’ve two earlier posts that play on the same effects – an image for Halloween and a classical scene.   I’ve always wondered if the effect would be even stronger and stranger in an animation.  So here it is.

Usually an area of the visual field within an outline, or more or less bounded by an outline, is either an object or an aperture.  (One of my earliest posts on the site is also about that).  We are so good at not getting those mixed up in everyday vision that when they get mixed up in a picture, like the Magritte painting or my examples, the effect is strangely disconcerting.

Thanks to Edweard Muybridge for the loan of the Cockatoo.

Dark Kanizsa Triangle

Here’s a dark-on-light, bubble version of The Kanizsa triangle.  The triangle is usually shown in white against black circles and lines, and can even look slightly brighter than background, though its edges are only indicated by the gaps in the lines and by the segments missing from the circles.   The brain adds the edges and fills in the triangle, as the most probable explanation for what’s missing.  The effect was created by Gaetano Kanizsa, as a demonstration of subjective contours, which in turn were first explored a bit over a century ago, as examples of Gestalt theory.  Bit of a link for enthusiasts that – ditto the following links – but if technical stuff is for you, there’s a great historical survey of the theory.  The theory as then developed is not now accepted, and just how the brain reconstructs the triangle is still debated.

Like many geometric illusions, and like the watercolour illusion (see recent post), the Kanizsa triangle also appears when reversed out as a black shape against bright lines and segments.  So here I’ve recruited some soap bubbles as a background to the effect.

As with other pictures on the site, unless an image is externally sourced, and we indicate that copyright may be asserted, you are welcome to download this images and use it for any private, non-commercial purposes.  But if you might like to buy a professionally produced print, check out our Cafepress site.

Stern, Smiling and Radiant Buddha

In this wonderful image of the Buddha from Bagan, Myanmar, facial expression changes from stern through smiling to radiant as the figure is viewed from increasing distance.  According to my friend Eddy Keon, the highest status members of the temple audience, along with temple officials, would have stood closest to the Buddha and therefore have experienced him at his sternest, whilst his radiance increased with the poverty of the viewer, banished to the back of the crowd.

The figure is the Kassapa Buddha, one of four Buddhas in the Ananda Temple, Bagan, Myanmar.  The city was the capital of the ancient Pagan kingdom, built, along with the temple and this figure of the Buddha, eight hundred years ago.

 The left hand and centre photos are from the brilliant travel blog of Forrestwalker.  The right hand image was taken by Eddy Keon.  His photo is so beautiful, here’s the whole thing.  Eddy hopes to use his pictures to support a hill village school in Myanmar.


Poggendorff Switch

If the way I see this animation is how most people do, the strength of the Poggendorff illusion can depend on our patterns of fixation when looking at it.  Adding distracting dots to the figure can attract the eye either obliquely along the parallels or at right angles across them.  To my eye, when the oblique track between the acute angles in the figure is labelled with flashing blobs, the strength of the illusion is reduced.  When the track at right angles across the parallels is labelled, effect is maximised.  The effect doesn’t change instantly for me, but settles down after each track has flashed two or three times.  I get the same effect if I switch fixations every second or so between equivalent blobs in still Poggendorff figures. The effect is strongest, as below, when the blobs are in the acute angles when the parallels are vertical, and across parallels when the parallels are horizontal.  So in the figure below, the illusion is not far off equal strength for me in the bottom pair of figures, but looks maybe a bit stronger at top left, and has almost vanished at top right.

If you’d like more on this, plus some additional demos, check out my site devoted to the Poggendorff illusion.

The Watercolour Illusion in Reverse

Here’s something I’ve not seen tried yet elsewhere:  a look at how the watercolour illusion (see three posts back) appears when reversed out, black to white.

Update 16/12/12:  My mistake! Here’s a report of an earlier study that does include reversal of the illusion.  It’s by Aula Dostoevsky and Ken Knolbauch.

In the original effect, as seen to left, islands with two-tone outlines seem tinted with the colour of the inner tone, if lighter than the outer, and otherwise appear (as in the lower figure) whiter than the background.

Sure enough, as seen centre, the effect is still there, but a bit weaker, when exactly the same two-tone outlines are placed on black.  The upper interiors, which seemed tinted on white, appear (to my eye) blacker than the black background.  The lower interior, which looked whiter than background on white, now appears tinted.  In other words, on white the haze spreads from the paler outline, when the darker outline encloses it, whereas on black, the haze spreads from the darker outline, and when enclosed by a paler outline.

Consistent with that, to my eye, on the right when the colours of the two-tone outlines are reversed on black, the interior that appeared tinted in the centre lower figure appears blacker than background.  The upper figures, with interiors blacker than background in the centre, look tinted to the right.

The effect is strongest for me in the three lower figures, looking across the whole image.  (Ignoring the Santa figure, added for seasonal effect).  For me the effect also works best slightly larger, so click on the figure to see a larger version.

Barrier-Grid (or Picket-Fence) Animation

In recent versions of these animations, as in the movie above, a grid of thin transparent lines in a mask is passed over a composite graphic image, to give an illusion of movement.  In earlier versions, made in France in the the 1920’s and called Ombro cinema or cinema enfantin, the grid of transparent lines was static in a viewing frame, and a strip of the composites was spooled behind it.  (There’s a nice demo from the North West Puppet Center in Seattle).

A beautiful recent booklet of barrier-grid animations is Colin Ord’s Magic Moving Images.  In 2006 a new  version of the technique, in which the act of opening a book automatically draws the grid over the image was patented by Rufus Butler Seder, called Scanimation. He’s also published a number great books for kids using his process.

By the way, there also used to be an entirely separate early computer animation machine, in the 1960’s, called The Scanimate).

In Seder’s and Ord’s books, the illusion happens in the real world, when you pass a real striped acetate mask over the composite base image. My demo is an animation that faithfully follows the real world process, as if a real striped mask was being passed over the base image.  I borrowed the jumping man from this composite photo by nineteenth century movement scientist Etienne Marey.

To make a barrier grid animation, you reduce the subject in each ‘frame’ of the original movie into a black silhouette, and then replace the black infill with a hatching of just a few vertical lines (turning the outline into a subjective contour, if you like a bit of technicality).

The hatched silhouettes are then combined into a composite image, like the one in the animation at the head of the post.  As the striped mask passes over it, only one frame at a time is revealed.  It’s fascinating that whilst the jumper in the final, striped silhouette above is barely recognisable as a figure, we see the jumper much more clearly in the movie. I find it a bit magical the way the jumper quite gradually appears in the movie as the mask begins to move over the composite image from the left. Our brains can discover figures in patterns of amazingly sparse data, if only they move coherently, as when the human body is represented just by dots at the key rotation points (such as knees and elbows).

Want to have a go at making a barrier grid animation yourself?

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The Watercolour Illusion

I’m currently giving a hand with an exhibition on the science and art of illusion, called IllusoriaMente, which will be on in Alghero, Sardinia (italy) in the first week in September, in association with the annual European Conference on Visual Perception.  During the preparations I’ve come across this illusion, which I’d heard of but not checked out.  It’s beautiful and extraordinary.  The areas bounded by three wiggly loops in the picture look different colours, as if just tinted with watercolour, but the effect depends on the brain doing the colouring in.  Each boundary is made up of a dark and a lighter strip.  The infilling always takes its cue from the colour of the lighter strip, and always in the direction from the darker strip towards and beyond the lighter strip.  So in this image, the effect is a bit paradoxical.  The colour appears inside the two islands on the left, in comparison with the white background.  Yet to the right the colouring is outside the island, with the island itself looking a brighter shade of white than the overall background.

Two different processes seem to be co-operating, a colouring effect, and a figure/ground effect, enhancing the separation between the surrounded areas and the background.  If you like a bit more technicality, there’s a Scholarpedia article, with references to academic papers, edited by Baingio Pinna, one of the pioneers researching into the effect (and the organsiser of this year’s ECVP conference in Alghero).

Note added at 10/12/12:  check out our slightly more recent post on the watercolour illusion in reverse.

Gustave Verbeek

Gustave Verbeek cartoon

About a hundred years ago one of the most popular newspaper comic-strip artists in America was Gustave Verbeek.  He contrived whole pages of pictures telling cartoon stories, which showed one sequence of scenes when viewed one way up, and the following set when turned upside down.  His best known adventures were those of Lady Lovekins and Old Man Muffaroo, each of them, as in the scenes above, always the inverse of the other.  His stories are so crazy and his drawings so imaginative that it can take a moment to realise one scene really is the exact inverse of the other.   His imagery is surrealist – long before surrealism emerged with artists like Salvador Dali in the establishment art world.

His cartoons have recently been reprinted (not cheap!)

Verbeek was developing an earlier tradition of rotating heads illusions, in which a head has one identity one way up, and another upside down.  See my first earlier post of that, with an animation, and another example with Santa turning into playwrite Henrick Ibsen

Drunken Dionysius

The butterflies appear to circulate in time to the heartbeat of Dionysius (the ancient Greek God of wine), yet they never change position.  The movement is an illusion.  Only the tones and colours are changing, and movement appears as light butterflies on a dark ground change to darker ones on a lighter ground, and as light edges of the butterflies change to dark, and vice versa.  You may also see similarly evoked movement on the chest and stomach of Dionysius, in time with his breathing.

Compression for Flash has rather trashed animation quality. If possible, view Drunken Dionysius as a
Quicktime Movie

Here’s a related illusion, a new version of the Duck/Rabbit illusion.

The yellow central panel appears to move, but remains objectively quite stationary.  The edges don’t move either, all that changes is that black edges switch to white, and vice versa.

These effects are related to those in the Bouncing Brains Illusion, an entry by Thorsten Hansen and colleagues (University of Giessen, Germany) for the Best Visual Illusion of the Year contest 2007.

They are also related to the peripheral drift illusion.  A beautiful new example of that illusion by Kaia Nao (aka wildlife artist Joe Hautman) was one of the final 10 entries in this year’s Best Visual Illusion of the Year contest (the whole contest is not to be missed!).

All these illusions are thought to arise in peripheral vision because of differences in the speed of brain processing of the light and dark edges of the elements in these patterns.  The ones presenting most contrast are processed quickest.  Because the timing differences and their direction across similarly orientated pattern elements are syncronised, they are picked up by movement detectors in peripheral vision, and interpreted as movement of whole blocks of elements. For another example of apparent movement in a completely static image, see our earlier Ocean Wave Illusion.

If you devour scholarly research articles, here’s one on what may be going on in these illusions in more detail.

Illusions and visual special effects – explanations and tutorials