Download Title of the presentation

Machine Vision Basics: Optics Part One
Webinar
Gregory Hollows
Director,
Machine Vision Solutions
Edmund Optics, Inc.
Celia Hoyer
Product Marketing
Vision Systems
Cognex Corporation
Agenda
• Introduction
• Optics Tutorial: Part One
•
•
•
•
Vision System Parameters
Resolution
Contrast
Modulation Transfer Function (MTF)
• Choosing a Lens: Part One
• Q&A
2
Introduction
Celia Hoyer, Product Marketing Manager
Cognex Corporation
“Three” Requirements for Machine Vision Solution
1. Vision System
2. Part
3. Illumination
4
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
Optics Tutorial: Part One
Gregory Hollows, Director, Machine Vision Solutions
Edmund Optics
Fundamental Parameters of Imaging/Vision Systems
7
Glossary of Terms
• Field Of View (FOV): The viewable area of the object
8
Glossary of Terms
• Working Distance (WD): The distance from the front of the
lens to the object
9
Glossary of Terms
• Resolution: The minimum feature size of the object
10
Glossary of Terms
• Depth Of Field (DOF): The maximum object depth that can
be maintained entirely in focus
11
Glossary of Terms
• Sensor Size: The size of a camera sensor’s active area,
typically specified in the horizontal dimension
12
Glossary of Terms
• Primary Magnification (PMAG): The ratio between the
sensor size and the FOV
13
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
Image Quality
Resolution
Depth of Field
Contrast
Image Quality
Perspective
15
Distortion
What is Resolution?
• Resolution is a measurement of the vision system's
ability to reproduce object detail
not resolved
16
resolved
Example: Field of View and Resolution
640 x 480 pixel
(0,5 megapixels)
17
1600 x 1200 pixel
(2,5 megapixels)
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
Resolution Comparison
High-resolution color
analog camera
19
High-resolution color
digital camera
Examples
20
Examples
21
Image Quality
Resolution
Depth of Field
Contrast
Image Quality
Perspective
22
Distortion
Image Quality
Depth of Field
Resolution
23
Contrast
Contrast
Color Filtering with a Monochrome Camera
No Filter
24
Red Filter
Green Filter
What Is Contrast?
• Contrast is the separation
in intensity between
blacks and whites
• The greater the difference
in intensity between a
black and white line, the
better the contrast
25
Imax - Imin
% Contrast =
Imax + Imin
How Does Contrast Depend On Frequency?
• When the spots are close enough that the contrast
becomes limiting, the spacing is our resolution
26
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
Frequency and Modulation Transfer Function (MTF)
28
Lens Comparison Testing Ronchi Ruling
29
Lens Comparison Testing Ronchi Ruling
30
Lens #1 Test
16mm Ronchi Test, 1.5 inch FOV 4 lp/mm object space resolution, 0.157 pmag, f1.4
Center 59%
Bottom Middle 56%
Corner 62%
F1.4 1.5 Inch FOV
250
200
150
Center
Bottom
Corner
100
50
0
390
31
400
410
420
430
440
450
460
Lens #2 Test
16mm Ronchi Test, 1.5 inch FOV 4 lp/mm object space resolution, 0.157 pmag, f1.4
Center 47%
Bottom Middle 42%
Corner 37%
F1.4 1.5 Inch FOV
250
200
150
Value
Value
Value
100
50
0
390
32
400
410
420
430
440
450
460
Lens #3 Test
16mm Ronchi Test, 1.5 inch FOV 4 lp/mm object space resolution, 0.157 pmag, f1.4
Center 52%
Bottom Middle 22%
Corner 36%
F1.4 1.5inch FOV
250
200
150
Center
Bottom
Corner
100
50
0
390
33
400
410
420
430
440
450
460
Image Comparison F1.4
Center
Lens #1
Lens #2
Lens #3
34
Bottom Middle
Corner
Examples
35
Examples
75mm lens
12mm lens
36
Examples
75mm lens
12mm lens
37
Quiz!
Celia Hoyer, Product Marketing Manager
Cognex Corporation
Quiz Question
• Which of these terms is defined as “The distance from
the front of the lens to the object”?
•
•
•
•
39
Field Of View (FOV)
Working Distance (WD)
Depth Of Field (DOF)
Primary Magnification (PMAG)
Quiz Answer
• Which of these terms is defined as “The distance from
the front of the lens to the object”?
•
•
•
•
40
Field Of View (FOV)
Working Distance (WD)
Depth Of Field (DOF)
Primary Magnification (PMAG)
Choosing a Lens: Part One
Celia Hoyer, Product Marketing Manager
Cognex Corporation
1. Define the Goals for Your Inspection
•
Type of inspection
•
•
•
•
•
•
Features to
highlight/minimize
•
42
Optical Character Recognition (OCR)
Code-reading
Assembly verification
Defect inspection
Dimensional gauging
Which two or more features need
contrast created?
2. Identify Constraints
•
Physical
•
•
•
•
•
Budgetary constraints
Speed
•
•
•
Exposure time
Motion
Environmental limitations
•
•
43
Space
Angle
Positioning
Washdown requirements
Temperature
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
Machine Vision Basics
• Optics Part Two
• Distortion, perspective and depth of field
• Optics Part Three
• CCD sizes
• Lens types and usage
45
Q&A