1) The human eye is a nearly spherical structure about 20mm in diameter that contains specialized cells and optical elements like the cornea, iris, and lens that work together to form images on the retina. 2) The retina contains light-sensitive rod and cone cells that detect images and transmit electrical signals through the optic nerve to the brain for visual perception. Rods function in low light and cones provide color vision and sharp central vision. 3) The human visual system can adapt to a wide range of light intensities through changes in brightness adaptation, but perceived brightness follows a logarithmic scale rather than the actual light levels. Optical illusions demonstrate how visual perception can differ from objective reality.

1. ELEMENTS OF VISUAL
PERCEPTION
Rafi Ullah (Ph.D Scholar)
Department of CS & IT University of Malakand

2. Contents of Presentation
• Visual perception
• Human Eye
• Structure of the Human Eye
• Image formation in the Eye
• Brightness adaptation and discrimination
• Optical Illusion

3. Visual perception

4. Visual perception
• Visual perception refers to the brain's
ability to make sense of what the eyes see

5. Visual Perception

6. The Human Visual System

7. Structure of the Human Eye

8. Human Eye
• Nearly spherical
• Diameter: Approx 20 mm
• 3 membranes enclose the eye
– Cornea (Cover anterior or front surface
of the eye), sclera
– Choroid
– Retina

9. Human Eye
• The complex physical process of
visualizing something involves the nearly
simultaneous interaction of the eyes and
the brain through a network of neurons,
receptors, and other specialized cells
• Human eye is equipped with a variety of
optical elements including the cornea, iris,
pupil, a variable-focus lens, and the retina

10. Human Eye
• Together, these elements work to form
images of the objects in a person's field of
view

11. Human Vision
• When an object is observed,
- it is first focused through the cornea and
lens onto the retina
• Retina is a multilayered membrane
- that contains millions of light sensitive cells
that detect the image and translate it into a
series of electrical signals

12. Human Vision
• These image capturing receptors of the
retina are termed
- rods and cones
• Cones and Rods are connected with the
fibers of the optic nerve bundle through a
series of specialized cells that coordinate the
transmission of the electrical signals to the
brain

13. Human Vision
• In the brain, the optic nerves from both eyes
join at the optic chiasma where information
from their retinas is correlated
• The visual information is then processed
through several steps, eventually arriving at
the visual cortex, which is located on the
lower rear section of each half of the
cerebrum (part of brain perform neural
function)

14. Human Vision
• Rods and cones are used to process
color in the light and dark (two
Sensors)

15. Human Vision
• Rods are responsible for processing
images in a dark atmosphere
• The cones (Color understanding) are
prominent in daylight
• The optic nerve primarily routes
information to the cerebral cortex,
where visual perception occurs

16. Human Vision
• A particularly specialized component of
the eye is the fovea centralis, which is
located on the optical axis of the eye in
an area near the center of the retina
• This area exclusively contains high-
density tightly packed cone cells and is
the area of sharpest vision

17. Human Vision

18. Human Vision

19. Human Vision

20. Human Vision
Cones and Rods
•In the human eye, there are two distinct
visual systems (based on two types of retinal
cells)
- Scotopic vision: Not color sensitive, more
sensitive to light and mainly peripheral (rods)

21. Human Vision
Cones and Rods
- Photopic vision : color sensitive, less
sensitive to light and mainly central (cones)

22. Human Vision
• Distribution of Rods and Cones in retina

23. Image formation in the Eye

24. Image formation in the Eye

25. Image formation in the Eye
• Example
Calculation of retinal image of an object
Distance between the center of the lens and retina( focal length) varies
from 17 mm to 14mm. C is the optical center of the lens.

26. Brightness Adaptation &
Discrimination
•The brightness adaptation is a phenomena
which describes the ability of the human eye
in simultaneously discriminating distinct
intensity level
•Brightness adaptation level is the current
sensitivity level of the visual system for any
given set of condition

27. Brightness Adaptation &
Discrimination
•The ability of the eye to discriminate between
different brightness levels is an important
consideration in creating and presenting
images
•The range of light intensity levels to which
the human visual system can adapt is on
the order of 1010
from the scotopic threshold
(minimum low light condition) to the glare
limit (maximum light level condition)

28. Brightness Adaptation &
Discrimination
Subjective brightness
•Subjective brightness is brightness as
perceived by the human visual system(HVS)
•Subjective brightness is a logarithmic
function
of the light intensity incident on the eye
•This characteristic is illustrated in the figure
below, which is a plot of light intensity versus
subjective brightness

29. Brightness Adaptation &
Discrimination

30. Brightness Adaptation &
Discrimination

31. Brightness Adaptation &
Discrimination

32. Brightness Adaptation &
Discrimination

33. Brightness Adaptation &
Discrimination
• The HVS cannot operate over such a
range simultaneously
• For any given set of conditions, the current
sensitivity level of HVS is called the
brightness adaptation level

34. Brightness Adaptation &
Discrimination

35. Brightness Adaptation &
Discrimination
At low level of light intensity

36. Brightness Adaptation &
Discrimination

37. Brightness Adaptation &
Discrimination
• The visual system cannot operate over such
a range simultaneously
• It accomplishes this large variation by
changes in its overall sensitivity. This
phenomenon is known as brightness
adaptation
• For any given set of conditions, the current
sensitivity level of the visual system is called
the brightness adaptation level

38. Brightness Adaptation
• Two phenomena clearly demonstrate that
perceived brightness is not a simple
function of intensity:
• Mach Bands
• simultaneous contrast

39. Brightness Adaptation

40. Brightness Adaptation

41. Brightness Adaptation
• The simultaneous contrast phenomenon:
each small square is actually the same
intensity but, because of the different
intensities of the surrounds, the small
squares do not appear equally bright

42. Brightness Adaptation

43. Optical illusion
• An optical illusion (also called a visual
illusion is an illusion caused by the visual
system and characterized by a visual
percept that appears to differ from reality
• The eye fills in non-existing information
or wrongly perceives geometrical
properties of objects

44. Optical illusion

45. Optical illusion

46. Optical illusion

47. THANK YOU