Various optical illusions in image processing compiled from various resources on web

1. OPTICAL
ILLUSIONS

2. Can you see dark blotches on the white
'junctions' in between the corners of these black
squares?

3. Which semicircle is brighter - the left or the right half?

4. One of the most famous optical illusions, reproduced in colour!

5. What line is longer;
from a to b, or from b to c?
Amazingly, they're both the same length. This is perhaps the most
extreme example of I have found that distorts perception of length.

6. Also created by Akiyoshi, the lines in this picture below are completely
parallel would you believe?

7. This amazing illusion to the right was created by Akiyoshi Kitaoka. It
already looks quite 'wavy', but try slowly moving the mouse cursor up
and down the center of the image - and focus on the cursor. You
should see the picture 'waving' in an incredible way.

8. At first, there doesn't seem anything unusual about this picture. I mean,
it's just a bunch of diagonal lines and a slightly distorted square in the
middle - right? Wrong.
Believe it or not, the 4 lines that make up the square are actually perfectly
straight. In fact it /is/ a perfect square. For proof of this, the animation will
swap between the two frames so you can see the square remains the
same. Also check by loading the pic into your favourite art package.

9. Rotating dot whirlpool
Wow! Try staring at this for more than 5 seconds
without going crazy. Then try following it round! =)
Curves constantly die out and then re-evolve as
part of another curve.

10. Is the following object physically possible?

11. Which line connects to line C? A or B?

12. Look at the grouping of stairs below. How can they keep climbing?

13. Is this knot pairing of triangles physically possible?

14. Despite their appearance, the top lines on each of
these trapezoids is the exact same size!

15. Can you figure out what this is a picture of?

16. Answer:Cow’s Head

17. ?????

18. The gear wheels should appear to SLOWLY rotate. The one on the left
side of the screen
should turn clockwise and the one on the right side of the screen
should turn counter-clockwise.

19. The green is identical throughout this illusion.

20. Drawing appears oblique but all the small squares have same size

21. Robots Appear to Dance

22. Impossible Construction

23. ???????

24. Cubes Appear to be Deformed

25. The image appears to move backward and forward

26. Look at the two circles below. Would you believe they are the same
color?

27. Does this scene look real to you?
It is painting….

28. In this classic optical illusion picture, palm trees appear to turn into
camels.

29. These three identical cars appear to be three different sizes.
Would you believe that they are all the same size? Try measuring
them to make sure.

30. This image makes it appear that the VW Beetles are being pulled
inward

31. Does this lucky clover appear to be in motion?

32. How is this Lego creation possible? These types of illusions can be
created in real life - it's all about the angle.

33. In this optical illusion, if you follow the movement of the rotating pink
dot with your eyes, the dots will remain only one color, pink. However, if
you stare at the black + in the center, the moving dot will turn green.
Keep concentrating on the black + in the center of the picture. After a
short period, all the pink dots will slowly disappear and you will only see
a single green dot moving in a circle.

34. The following are common tests used to detect color blindness.
Can you read the numbers hidden in each square?
You should see 58 (upper left), 18 (upper right), E (lower left) and 17
(lower right).
If you cannot see any of the above numbers/letters, you may suffer
from color blindness.

35. Mach Band Effect
• The what? The Machband describes an effect where the human mind subconsciously
increases the contrast between two surfaces with different luminance. It can be seen on
the index page of this website.
•
• The luminance of the squares above increases in a stepwise fashion. However although
the luminance within each block is constant the apparent lightness of each strip seems
to vary across its length. Close to the left edge of the strip it appears lighter than at the
centre, and close to the right edge of the strip it appears darker than at the centre. The
visual system is exaggerating the difference in luminance (contrast) at each edge in
order top detect it. Try holding a pencil over an edge in this image and see how the
apparent difference in lightness of two adjacent strips changes. They become much
harder to tell apart. The edge detection is working to enhance object separation.
• Mach banding is caused by lateral inhibition of the receptors in the eye. As receptors
receive light they draw light-sensitive chemical compounds from adjacent regions, thus
inhibiting the response of receptors in those regions. Receptors directly on the lighter
side of the boundary can pull in unused chemicals from the darker side, and thus
produce a stronger response. Receptors on the on the darker side of the boundary,
however, produce a weaker effect because of that same migration.

36. Mach Bands
• Mach bands are an optical illusion named after Ernst Mach consisting of an image of two wide
bands, one light and one dark, separated by a narrow strip with a light-to-dark gradient. Humans
perceive two narrow bands of different brightness on either side of the gradient that are not
present in the original image. The effect is like that of a spatial high-boost filter
The illusion is usually supposed to be caused by lateral inhibition of the receptors in the eye.
According to lateral inhibition, given that the gradient is horizontally oriented, the brain
interprets the image as a collection of vertical lines. Every stripe has a value but the brain
calculates the contrast of a stripe in relation to neighbor stripes. Stripes at the edges of the
gradient have less lateral inhibition than the stripes in the uniform area so they appear as if
they are brighter or darker than their real value.

37. Match Bands
Illusory Mach Bands result when gradients
from darker to lighter shades are created.
The thin light and dark bands are illusory.
Below the effect is doubled

38. Match Bands
Mach Bands also occur with a related
circular effect.
Notice the the slight glow that extends.
Addition a second gradient enhances the
effect and almost seems to produce an
entire glowing area..
Addition of a third gradient produces an even stronger effect.
Now the glow is striking and the center
yellow seems much brighter that the yellow
in each corner. Also, there is a difuse but
strong subjective contour effect

39. Match Bands
Move closer to and further from the screen
while looking at the center of the figure.
There is a change in apparent brightness.
This effect is covered in more detail in the
section on Dynamic Luminance.

40. Optic"Spirals of fluorescent color"
Red appears to be fluorescent color and scintillate.
Moreover, red appears to be pink or orange in the center.

41. "Dongirarin"*
*"Donguri" means acorns and "girarin" means scintillation
Rings appear to rotate as well as the figure scintillates.

42. "Donguriko"*
*"Donguri" means acorns, "ko" means a container, and "domburakokko" means the
sound of floats on a flow of water.
Rows appear to move leftward or rightward.

43. "Throwing cast nets"
Circles appear to expand.

44. "Rotating snakes 3"
Rings of snakes appear to rotate

45. "Chrysanthemums"
Flowers appear to expand.

46. "Rotating snakes"
Circular snakes appear to rotate 'spontaneously'.

47. "Packed cans"
The upper and lower rows appear to move leftward while the middle row
appears to slide rightward.

48. "Rotating spiral snakes"
Snakes appear to rotate (peripheral drift illusion*1). Gray concentric circles
appear to be a spiral (spiral illusion*2).

49. "Into the space"
The surround appears to rotate clockwise.