1. Version 0.10 (c) 2007 CELEST VISI  N BRIGHTNESS CONTRAST CLASSROOM PRESENTATION PRE-EXPERIMENT How many black dots can you count?

2. Version 0.10 (c) 2007 CELEST WHITE’S ILLUSION How many shades of gray are in the picture?

3. Version 0.10 (c) 2007 CELEST Are squares A and B the same shade of gray? ADELSON’S CHECKERED SHADOW ILLUSION

4. Version 0.10 (c) 2007 CELEST COMMON MISCONCEPTION ABOUT VISION: EXTRA-TRANSMISSION Some people believe that when they look at something energy or waves are emitted from the eyes – extra- transmission “Extra” means out “transmission” means to send or move

5. Version 0.10 (c) 2007 CELEST If vision is dependent on light entering the eye, CAN YOU SEE THINGS IN THE DARK?

6. Version 0.10 (c) 2007 CELEST HOW DO WE SEE? However, vision is a perceptual process involving many parts of the brain that do not work like a camera. Because sight is based on light entering the eyes, it might appear that our eyes work like cameras to produce images of objects.

7. Version 0.10 (c) 2007 CELEST Consider this: When we turn on a light bulb it produces light Not all objects produce light, but all visible objects reflect light into our eyes. This reflected light enables us to see the object Luminance : Amount of reflected light energy that enters the eye. Illuminant: Light source. Illuminance: Amount of light energy emitted from a light source. Illuminance is measured in lux (lx).

8. Version 0.10 (c) 2007 CELEST When light falls on a surface, some of it is absorbed and some of it is reflected. HOW DO WE SEE OBJECTS THAT DO NOT PRODUCE LIGHT? reflected absorbed Our eyes can detect the reflected light. *The wavelengths of light reflected determine the color(s) we see.

9. Version 0.10 (c) 2007 CELEST DARK AND LIGHT SURFACES absorb most of the light that falls on them, and reflect little. reflected absorbed reflected absorbed Dark surfacesLight surfaces absorb little of the light that falls on them, and reflect most.

10. Version 0.10 (c) 2007 CELEST If vision is dependent on light entering the eye, CAN YOU SEE THINGS IN THE DARK? No light… …no sight!

11. Version 0.10 (c) 2007 CELEST EDGE DETECTORS! Visual perception is sensitive to the difference or contrast between two surfaces. In terms of vision, contrast is the comparison between the reflected light of one surface and another.

12. Version 0.10 (c) 2007 CELEST WHAT IS “PERCEPTION”? Some perceptions are illusory. Perception is the process of acquiring, “interpreting,” selecting, and organizing sensory information. Do you always see what is “really” there?

13. Version 0.10 (c) 2007 CELEST How does the human brain and eye accomplish the task of perceiving?

14. Version 0.10 (c) 2007 CELEST THE HUMAN EYE www.dailynexus.com The eye is actually an organ in the shape of a ball. From the outside you can see the pupil and the iris. The pupil is an opening that permits light to enter the eye. The iris is the muscle that controls the size of the pupil. Pupil Iris

15. Version 0.10 (c) 2007 CELEST The light bends when it passed through the cornea, then enters the pupil. The lens bends the light to focus an image on the retina at the back of the eye. The photoreceptors receive the light image and send information to the brain via the optic nerve.

16. Version 0.10 (c) 2007 CELEST VISION AND THE BRAIN Light stimulates photoreceptors sending messages to the visual cortex.

17. Version 0.10 (c) 2007 CELEST THE VISUAL PATHWAY Adapted from Frisby 1979

18. Version 0.10 (c) 2007 CELEST BASIC DEFINITIONS Luminance: Amount of reflected light energy that enters the human eye after being reflected from the surface of objects. Luminace is measured in candela per square meter (cd/m 2 ). http://reu.uwosh.edu/vaughan.php REFLECTED LIGHT Illuminant Illuminance Luminance Photoreceptors on the retina Illuminant: Light source. Illuminance: Amount of light energy emitted from a light source. Illuminance is measured in lux (lx).

19. Version 0.10 (c) 2007 CELEST BASIC DEFINITIONS Reflectance: Physical property of an object’s surface. Calculated by a ratio of luminance divided by illuminance. Reflectance is measured in percentage (%). http://reu.uwosh.edu/vaughan.php REFLECTED LIGHT Reflectance Photoreceptors on the retina Brightness Perception Brightness: A subjective measure of the perception of luminance.

20. Version 0.10 (c) 2007 CELEST MODELS The most abstract models are mathematical representations where variables represent realities. We can develop a better understanding of vision using models. A model is an abstract representation of an everyday experience. Some models look very similar to what they represent, other models are more abstract--like a diagram of the situation.

21. Version 0.10 (c) 2007 CELEST = ILLUMINATION, REFLECTANCE, AND BRIGHTNESS R(a) = E1E1 I1I1 Illuminance: I 1 Luminance: E 1 a R = E I Brightness constancy is due to discounting the illuminant. In general: Reflectance = Luminance Illuminance The reflectance has the same value under different lighting conditions. = E2E2 I2I2 Illuminance: I 2 Luminance: E 2

22. Version 0.10 (c) 2007 CELEST =R(b) R(b) R(a) E(a) a b E(b) R  E I E(a)/I E(b)/I = E(a) E(b) BRIGHTNESS PERCEPTION IS BASED ON COMPARING TWO SURFACES R(a) R(b) === E(a) I E(b) I x E(a) I E(b) I ÷ The contrast between two surfaces is compared as a ratio of their luminances.

23. Version 0.10 (c) 2007 CELEST CALCULATING CONTRAST Inner A appears brighter than inner B because of higher contrast.  2.0 = 200%0.5 (50%) AB Inner Outer E(inner A) E(outer A) E(inner B) E(outer B) Contrast = 50 25 50 100 

24. Version 0.10 (c) 2007 CELEST MODELS OF BRIGHTNESS CONTRAST PHYSICALSIMILARABSTRACT R(a) R(b) R(b) = E(b) I R(a) = E(a) I BRIGHTNESS CONTRAST REFLECTANCE

25. Version 0.10 (c) 2007 CELEST WHITE’S ILLUSION How many shades of gray are in the picture?

26. Version 0.10 (c) 2007 CELEST WHITE’S ILLUSION Only one!

27. Version 0.10 (c) 2007 CELEST Are squares A and B the same shade of gray? ADELSON’S CHECKERED SHADOW ILLUSION

28. Version 0.10 (c) 2007 CELEST Yes! ADELSON’S CHECKERED SHADOW ILLUSION

29. Version 0.10 (c) 2007 CELEST BRIGHTNESS CONTRAST REVISTED AB Inner Outer Can you believe that the reflectance of Inner(A) is EQUAL to the reflectance of Inner(B)? Why did the inner boxes appear to be the same now? Inner