1. How to create 3D using 2D? Artists use the following depth cues to convey 3D impression Size Geometrical perspective Shadow Color Sharpness Patterns Overlay (interposition) However, they are intrinsically ambiguous, can be interpreted in many ways. We interpret in the most likely possibility.

2. A counter example: impossible triangle developed by Roger Penrose and his father

3. Escher One of Escher's marvelous impossible buildings. The basis of the illusion is the inclusion of the impossible triangle or tri-bar.

4. Escher also used this principal in Ascending/Descending, The Impossible Staircase. The triangle is placed into the picture three times. As you look at each part of the construction in the print you cannot find any mistakes, but when the print is viewed as a whole you see the problem of water traveling up a flat plane, yet the water is falling and spinning a miller's wheel. How do the two towers appear relatively the same height yet the left side rises three stories and the right two? Why did Escher chose to use underwater plant life, greatly magnified, as his choice for an above watergarden? The illusion in this print, when viewed by most people, is not seen on the first look.

5. Size Smaller objects are more distant, and closer objects are larger. However Movie producers use this to fool us: take a close picture of miniature models to get an illusion of the distance objects or vice versa. “Honey, I shrunk the kids” Architects: using smaller window at higher floors.

7. Geometrical perspective Parallel receding lines appear as if they are coming together. (rail road tracks, light rays from the sun) In architecture Narrower towards the top or the other end. In art Da Vinci’s “last supper”

10. Shadow Shadows are extremely important in providing us the 3D impression. Light color appears closer to us and hence bigger.

13. Variations in Color Distant landscapes tend to lose their color contrasts. Colors get duller, less pure. A color print seems to have more depth than the identical picture printed in black and white, and shadows can be conveyed without variation in brightness. Distant mountains appear blue due to the blueness of the intervening air.

15. Variations in Sharpness Distance objects appear fuzzier, less sharply focused. Images are smaller in the retina. (oil painting) Artists convey the feeling of depth by a loss of detail in distant objects.

16. Patterns An abstract pattern may create the feeling of depth. Use by Vasarely and Mattise in paintings.

19. Overlaying We perceive one object to be farther than another if the second object blocks our view of the first. However, the apparently more distant object may in fact be closer but cut in such a shape that it fully reveals the apparently closer (but actually farther) object.

21. Previous knowledge You interpret an image according to the previous knowledge stored in your brain. An interpretation against common experience is suppressed. Inside-out face (Disneyland) Cube Stairs