Machine Vision Basics: Optics Part One

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1 Machine Vision Basics: Optics Part One Webinar Gregory Hollows Director, Machine Vision Solutions Edmund Optics, Inc. Celia Hoyer Product Marketing Vision Systems Cognex Corporation

2 Agenda Introduction Optics Tutorial: Part One Vision System Parameters Resolution Contrast Modulation Transfer Function (MTF) Choosing a Lens: Part One Q&A 2

3 Introduction Celia Hoyer, Product Marketing Manager Cognex Corporation

4 Three Requirements for Machine Vision Solution 1. Vision System 2. Part 3. Illumination 4

5 Adding a Lens to Enhance Your Image 1. Locate features within the Field of View (FOV) 2. Ensure features are in focus 3. Avoid perspective distortion 4. Maximize contrast 5

6 Optics Tutorial: Part One Gregory Hollows, Director, Machine Vision Solutions Edmund Optics

7 Fundamental Parameters of Imaging/Vision Systems 7

8 Glossary of Terms Field Of View (FOV): The viewable area of the object 8

9 Glossary of Terms Working Distance (WD): The distance from the front of the lens to the object 9

10 Glossary of Terms Resolution: The minimum feature size of the object 10

11 Glossary of Terms Depth Of Field (DOF): The maximum object depth that can be maintained entirely in focus 11

12 Glossary of Terms Sensor Size: The size of a camera sensor s active area, typically specified in the horizontal dimension 12

13 Glossary of Terms Primary Magnification (PMAG): The ratio between the sensor size and the FOV 13

14 Glossary of Terms Field Of View (FOV): The viewable area of the object Working Distance (WD): The distance from the front of the lens to the object Resolution: The minimum feature size of the object Depth Of Field (DOF): The maximum object depth that can be maintained entirely in focus Sensor Size: The size of a camera sensor s active area, typically specified in the horizontal dimension Primary Magnification (PMAG): The ratio between the sensor size and the FOV 14

15 Image Quality Resolution Depth of Field Contrast Image Quality Perspective Distortion 15

16 What is Resolution? Resolution is a measurement of the vision system's ability to reproduce object detail not resolved resolved 16

17 Example: Field of View and Resolution 640 x 480 pixel (0,5 megapixels) 1600 x 1200 pixel (2,5 megapixels) 17

18 Testing Resolution Find a limiting resolution with a test target Targets consist of varying frequencies Bar target Sets of line pairs Orthogonal bars allow tests of astigmatic errors Limited by a finite number of steps in frequency 18

19 Resolution Comparison High-resolution color analog camera High-resolution color digital camera 19

20 Examples 20

21 Examples 21

22 Image Quality Resolution Depth of Field Contrast Image Quality Perspective Distortion 22

23 Image Quality Depth of Field Resolution Contrast Contrast 23

24 Color Filtering with a Monochrome Camera No Filter Red Filter Green Filter 24

25 What Is Contrast? Contrast is the separation in intensity between blacks and whites % Contrast = I max -I min I max + I min The greater the difference in intensity between a black and white line, the better the contrast 25

26 How Does Contrast Depend On Frequency? When the spots are close enough that the contrast becomes limiting, the spacing is our resolution 26

27 Feature Contrast and Modulation Transfer Function (MTF) A measurement of the ability of an optical system to reproduce (transfer) various levels of detail from the object to the image, as shown by the degree of contrast (modulation) in the image Line Pairs per mm (LP/mm) 27

28 Frequency and Modulation Transfer Function (MTF) 28

29 Lens Comparison Testing Ronchi Ruling 29

30 Lens Comparison Testing Ronchi Ruling 30

31 Lens #1 Test 16mm Ronchi Test, 1.5 inch FOV 4 lp/mm object space resolution, pmag, f1.4 Center 59% Bottom Middle 56% Corner 62% F Inch FOV Center Bottom Corner

32 Lens #2 Test 16mm Ronchi Test, 1.5 inch FOV 4 lp/mm object space resolution, pmag, f1.4 Center 47% Bottom Middle 42% Corner 37% F Inch FOV Value Value Value

33 Lens #3 Test 16mm Ronchi Test, 1.5 inch FOV 4 lp/mm object space resolution, pmag, f1.4 Center 52% Bottom Middle 22% Corner 36% F inch FOV Center Bottom Corner

34 Image Comparison F1.4 Center Bottom Middle Corner Lens #1 Lens #2 Lens #3 34

35 Examples 35

36 Examples 75mm lens 12mm lens 36

37 Examples 75mm lens 12mm lens 37

38 Quiz! Celia Hoyer, Product Marketing Manager Cognex Corporation

39 Quiz Question Which of these terms is defined as The distance from the front of the lens to the object? Field Of View (FOV) Working Distance (WD) Depth Of Field (DOF) Primary Magnification (PMAG) 39

40 Quiz Answer Which of these terms is defined as The distance from the front of the lens to the object? Field Of View (FOV) Working Distance (WD) Depth Of Field (DOF) Primary Magnification (PMAG) 40

41 Choosing a Lens: Part One Celia Hoyer, Product Marketing Manager Cognex Corporation

42 1. Define the Goals for Your Inspection Type of inspection Optical Character Recognition (OCR) Code-reading Assembly verification Defect inspection Dimensional gauging Features to highlight/minimize Which two or more features need contrast created? 42

43 2. Identify Constraints Physical Space Angle Positioning Budgetary constraints Speed Exposure time Motion Environmental limitations Washdown requirements Temperature 43

44 Summary Lighting and Optics are important and keys to the overall solution Approach problems with a process Ask questions Test the options Do not settle on the first solution Don t leave lighting and optics testing to the end Find trusted partners 44

45 Machine Vision Basics Optics Part Two Distortion, perspective and depth of field Optics Part Three CCD sizes Lens types and usage 45

46 Q&A

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