Taking bubble pictures

Here’s a picture to introduce a post about how I take photos of soap bubbles. OK, I admit I didn’t snap this one out of an aeroplane window. I also admit that Photoshop had something to do with it, and I’ll get to that in later Photoshop posts. But the bubbles start out as real bubble photos, and if you wonder how, read on below.  (If you’d just like some bubble pictures for your own site, there are two you can link to on our page of link thumbnails, and I’ll be adding many more later.  There’s an earlier post too, with another bubble picture. Or if you need easy presents for someone, why not browse some fun bubble image and illusion stuff to buy.)

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Competing illusions


Here’s a rather subtle effect. It’s a competition underway, when the Zollner illusion is seen embedded in a staircase. In the staircase lower left, where two of the long lines are either side of the outside edge of a step (in other words like lines a and b here, on the sides of a convex step), the lines seem to get further apart with distance, as they would in a normal presentation of the Zollner illusion. But wherever on that lower left stair the lines are like b and c here, either side of the inner edge of a step, (so on a concave step), they tend to look much more parallel. In a normal version of the illusion, as below, the equivalent long lines appear to get closer together to the right.

Want to know more?

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Making illusion images with Photoshop CS3

Here’s a paradoxical image to introduce the subject of drawing illusions in Photoshop CS3.  The two arrows are objectively aligned, and if you try to ignore the folding screen shape in between, they look to me not so far off that.  But now look at the short segments of the folding screen that they line up with. Those segments are also aligned, but concentrate on them and they look so far out of alignment to me, I have to keep checking I haven’t got the figure wrong!  It’s a turbo variant of the Poggendorff illusion.

I like to draw my figures in Photoshop CS3, because I’ve already got it, and it’s on many people’s machines if I’m on the move. But it’s not designed primarily for that sort of drawing, especially of geometric shapes, like the ones in the illusion above, so it’s not always ideal. However, I can always find a way of doing what I want, so here is the first of a series of posts, with hints about things I found tricky at first. However, as you’ve surely discovered, there are often lots of ways of doing the same thing in CS3. I’m no Photoshop expert, and if you know a better way, please leave a comment.

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The Poggendorff Illusion and depth processing

One of the most obstinately puzzling illusions is Poggendorff’s, in which a slanting line interrupted by a gap no longer looks aligned. For over a century specialists have been unable even to agree whether it arises from 2D properties of the image, or as a result of attempts by the brain to interpret the configuration as 3D. Papers written a hundred years ago treat the problem in very much the same terms as we do today. I’m betting on 2D (I argue for that on another, website devoted to the Poggendorff illusion). It’s not likely my speculations are spot on, and they may well not even be in the right direction. But read on here if you’d like to see demonstrations that show why I don’t think depth processing can be the answer.

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Paradoxical Size Constancy

Size constancy is the term for our tendency to see distant objects as larger than they are. So the far end of a shape with parallel sides looks wider than the near end. (See the earlier post on The Wonky Window). It seems to be such a basic feature of vision that it can give rise to amazing effects.  In the photo, first note note that the “sculpture” is impossible! All four blocks are receding from us, so they could only connect up in real space as a bendy snake. Instead they join up in an impossible, ever-receding, endless loop.  (See the earlier post on M.C.Escher’s Waterfall for how that kind of impossible figure works). Here the endless loop leads to a paradox, thanks to size constancy. The distant end of each block seems wider than the near end, and yet at the same time seems to be exactly the same size as the apparently smaller, near end of the next block. Measure the sides of the blocks and you’ll find them parallel. It’s one of many demonstrations that perceptual space is not always geometrically consistent, (or it can be non-Euclidean, as the specialists put it).


I located my impossible sculpture in a deeply receding space because that makes the effect just a bit stronger.

Update January 2010: How could I have overlooked this?  The stripes I’ve added to these blocks will be enhancing the effect of divergence by adding the chevron illusion to the size-constancy effect.  The chevron illusion was first reported 500 years ago, by French writer Montaigne, as related in Jaques Ninio’s book on illusions, page 15.  The chevron effect is a special case of the illusion later re-discovered a bit over a century ago as the Zollner illusion.  Some specialists would say both effects depend on the brain’s attempts to make sense of figures as shapes in space.  I suspect that’s true of the size-constancy effect, but that the chevron effect is 2D, pattern driven.  That seems supported by the observation that whilst in the picture above the chevron and size-constancy effects are acting in consort, they can also oppose one another, reducing the effect of divergence.

Read on for more on size-constancy.

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An Ambiguous Skull-Mask Illusion

Is this a picture of a mask looking at a skull it’s holding up for inspection, or vice versa?

I got the idea from a print by Picasso, Young man with mask of a bull, faun and profile of a woman. There’s a copy in the Art Gallery of New South Wales in Sydney, and you can see it by calling up,


search for Picasso, scroll down the results and you’ll find it!

Classic illusion books


Here’s another rotating head illusion, just to introduce a list of my favourite illusion books. It’s not one you’ll find in the books, because I only just drew it.  Still, that leaves plenty of old illusions, and there are stacks of fun books on the subject, many of them excellent. Here are some I think are real classics:

Richard GREGORY, Eye and Brain: the psychology of seeing (5th Ed.) OUP 1998

The standard introduction to vision and illusions, say, sixth form to first year college level, authoritative but great fun.


J.O.ROBINSON, The Psychology of Visual Illusion, New Ed., Dover Pubs, 1998

A bit more technical, but with a comprehensive selection of geometric illusions.


Jacques NINIO, The Science of Illusions, Cornell Uni Press 2001

Another fascinating general introductory text, by an eminent researcher


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Tessellations with figures

A tessellation is a pattern made up of elements that repeat with no gaps and no overlaps.  The elements may be abstract shapes, or may be recognisable objects or creatures, like the ones in the tessellations of M.C.Escher.  When I begun playing around with tessellations, I thought understanding the procedures needed to make patterns that tessellate would be the hard part.  I thought it would be fairly easy to find creatures in whatever shapes I ended up with.  Not so.  The procedures aren’t so hard.  But fitting creatures into them I found really difficult.  Here’s one of my first attempts.  I started with one of the most complicated recipes for a tessellation.  


For the details of the procedures, which give shapes that tessellate, see my tessellation tutorial. Essentially, the boundary of every shape that will tessellate is made up of pairs of lines. Within each pair, an identical line repeats, either by rotation, reflection, or just by shifting over. In the example above, there are four pairs of lines, two of them with rotations and two with reflections.

But what creature could I discover in this shape? Here’s what I came up with, a cross between an elephant and a rhino, with a little man on its back.

And it does tessellate!  It gives a pattern in which the elenoceros repeats four times, right way up facing both ways, and then upside down facing both ways.

Illusions and visual special effects – explanations and tutorials