2. Vision Basics
Lighting I

3. Vision Basics Lighting I Contrast Backlight Lighting Geometry
Effects of Color

4. Contrast is achieved through proper lighting
Creating Contrast
CONTRAST
It’s all about 
CONTRAST
A Successful vision application creates optical contrast between the feature of interest and the background
Contrast is achieved through proper lighting

5. Evaluate the Optical Properties
Determine what separates the good parts from the bad parts
Which optical property or properties can be used to generate CONTRAST
? Color ? Shape ? Texture ? Translucency ?
This technique reduces the number of light that must be tested, but does not eliminate testing

6. Lighting is Very Important
What are the most important optical components in any vision application?
The PART and the BACKGROUND
The Object or Feature of Interest
The Background
Lighting is used to create this contrast
Lighting and Optics are %80 of any vision application!

7. Lighting is Very Important
Keep in mind…
Proper lighting creates CONSISTENT contrast
Vision tools work better when lighting is repeatable and well controlled
In general, software cannot fix lighting problems

8. Optical Properties
What optical properties can be used to create contrast?
Color
Shape
Surface Texture
Translucency

9. Vision Basics
Backlight

10. Backlight Even, diffused light is emitted behind the part
Opaque areas = dark (silhouette)
Translucent areas = gray
Transparent areas = bright
Unblocked areas = white

11. Backlight - Translucency
Light transmits differently through section of transparent parts creating contrast between features

12. Blurry Edges

13. Method 1 – Block Light Block the light that is causing the problem
No light can hit upper surfaces on party

14. Method 2 – Move Part Move part farther away from Backlight
Light can not hit upper surfaces on part

15. The Solution = Collimation
Collimated Light
Uncollimated Light
Collimated light solves this blurring problem
2 methods to help collimated the light being emitted by a highly diffused backlight
Block light
Target farther away from Backlight

16. Close Backlight

17. Far Backlight

18. Backlight in the real world
Ring Light
Lamp Filament
Backlight

19. Backlight in the real world
Cap presence and position on a vial

20. Backlight in the real world
Metal pins through a plastic connector

21. Vision Basics
Lighting Geometry θ θ

22. Lighting is Very Important
What type of lights are used to create Geometric affects?
Directional
Area
Linear Array
Ring
On-Axis
Low Angle Ring

23. Reflection Geometry Light reflects at the angle of incidence
Angle of incidence = Angle of reflection θ θ
Lighting is a lot like pool; All about angles

24. Microscopic View of Surface
Reflection Geometry
If we illuminate this flat shiny surface will the camera see the light?
No, the light reflects at the angle of incidence
Light reflects away from the camera θ θ
Microscopic View of Surface

25. Microscopic View of Surface
Reflection Geometry
If we illuminate this rough surface will the camera see the light?
Yes, only some light θ θ
Microscopic View of Surface

26. Bright-Field vs Dark-Field
Bright-Field Area
Dark-Field Area
Dark-Field Area
FOV

27. Surface Texture and Geometry
Light/Method
Smooth surfaces appear…
Rough surfaces appear…
Directional
Bright-Field
BRIGHT
DARK
DARK
BRIGHT
Directional
Dark-Field
Low Angle
DARK
BRIGHT
On Axis
BRIGHT
DARK

28. Directional Light in the Real World
Reduce Glare
Same exposure time and gain
Only light position changed

29. Directional Light in the Real World
Different surface textures
Bright Field vs Dark Field

30. Directional Light in the Real World
Highlight presence and Absence
Same exposure time and Gain
Only light position changed
Cast Shadows

31. Low Angle Light

32. Low Angle Light
Dark-Field Illumination

33. Low Angle Light in the Real World
Water drops on silicon

34. Low Angle Light in the Real World
Features of a plastic lid

35. On-Axis Light

36. On-Axis Light
Bright-Field Illumination

37. On-Axis Light in the Real World
Light deflected by presence of solder
Light deflected by presence of solder

38. On-Axis vs Low Angle Lights
Opposite Illumination Effects
On-Axis light
Low Angle light

39. On-Axis Light in the Real World
Laser code on metal shaft

40. On-Axis Light in the Real World
Missing pins in connector

41. Vision Basics
Effects of Color

42. Color
A perception of wavelength

43. Color – Human Eye Response
Three types of cone cells in the eye
Each responds differently light’s wavelength

44. Human Eye Net Response

45. Imager Chip Responses

46. Emitted Spectra - Red LED
Only red wavelengths present = Red Light

47. Incandescent Light Bulb
All visible wavelengths present = White Light

48. Vision Basics Two ways to create CONTRAST using color Additive
Shine the color of light your are interested in on the part
Subtractive
Use a filter to remove the wavelengths of light you do not want

49. Reflected Spectra
Incoming white light
Reflected red light

51. Color Wheel Facts to remember about color Reflection
A BLUE object appears that color because it reflects BLUE light
To make a GREEN object appear bright, shine GREEN light on it
Complementary Colors
To make a GREEN object appear dark, shine RED light on it
(Shine any color other than GREEN)

52. Color Wheel
3 Color target

53. Color Wheel
Gray scale vision sensor with White light

54. Color Wheel
Gray scale vision sensor with Red light

55. Color Wheel
Gray scale vision sensor with Green light

56. Color Wheel
Gray scale vision sensor with Blue light

57. Color Lens Filters
Filters only let certain wavelengths pass through

58. Color in the Real World Blue Light Green Light Red Light White Light
PCB fiducial application

59. Color in the Real World
Original
White
Light
No Filter
Red Filter

60. Vision Basics
Summary

61. Summary

63. Summary
Optical Properties
Shape
Surface Texture
Color
Translucency

64. Summary
What lighting technique can be used to highlight differences in shape
Backlight
Directional Light (Area Light)
Low Angle ight
On-Axis light

65. Summary
What lighting technique can be used to highlight differences in surface texture
Directional Light (Area Light)
Low Angle light
On-Axis light

66. Summary
What lighting techniques can be used to highlight differences in color?
Color filters and color lights