Xử lý ảnh trong cơ điện tử: Machine Vision. Chapter 1. Introduction to machine vision93

Illumination ❖Lighting Types >> Ring Light SICK IVP, “Machine Vision Introduction,” 2006... Illumination ❖Lighting Types >> Spot Light SICK IVP, “Machine Vision Introduction,” 2006... Il

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XỬ LÝ ẢNH TRONG CƠ ĐIỆN

Machine Vision

TRƯỜNG ĐẠI HỌC BÁCH KHOA

Giảng viên: TS Nguyễn Thành Hùn

Đơn vị: Bộ môn Cơ điện tử, Viện Cơ

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Chapter 1 Introduction to machin

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1 Introduction

❖Deﬁnition

➢Machine vision (MV) is the technology and methods used to based automatic inspection and analysis for such applications asinspection, process control, and robot guidance, usually in indus

➢Machine vision is a term encompassing a large number of tecsoftware and hardware products, integrated systems, actions, meexpertise

➢ Machine vision as a systems engineering discipline can be consfrom computer vision, a form of computer science

➢ It attempts to integrate existing technologies in new ways and asolve real world problems

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1 Introduction

❖Deﬁnition

➢ The overall machine vision process includes planning the detailrequirements and project, and then creating a solution During rprocess starts with imaging, followed by automated analysis of extraction of the required information

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1 Introduction

❖Deﬁnition

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1 Introduction

❖Application: Locate

➢ To find the object and report its position and orientation.

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1 Introduction

❖Application: Measure

➢ To measure physical dimensions of the object

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1 Introduction

❖Application: Inspect

➢ To validate certain features

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1 Introduction

❖Application: Inspect

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1 Introduction

❖Application: Identify

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Chapter 1 Introduction to machin

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2 Basic elements of machine visio

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❑ 2.1 Overview

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How to automatically detect the d

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❖Illumination

➢ Illumination: is the way an object is lit up and lighting is the actgenerates the illumination

❖Imaging (Camera and lens)

➢ The term imaging defines the act of creating an image

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❖Image processing and analysis

➢ This is where the desired features are extracted automatically byconclusions are drawn

➢ A feature is the general term for information in an image, for exdimension or a pattern

➢ Algorithms are also referred to as tools or functions

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❑ 2.2 Illumination

❖The goal of lighting in machine vision is to obtain a robust appl

➢ Enhancing the features to be inspected

➢ Assuring high repeatability in image quality

SICK IVP, “Machine Vision Introduction,” 2006.

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❖Illumination Principles

Light can be described as waves with three properties:

➢ Wavelength or color, measured in nm (nanometers)

➢ Intensity

➢ Polarization

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➢ The optical axis is a thought line through the center of the lenthe camera is looking

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❖Lighting Types >> Ring Light

➢ A ring light is mounted around the optical axis of the lens, eithesomewhere in between the camera and the object

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❖Lighting Types >> Ring Light

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❖Lighting Types >> Spot Light

➢ A spot light has all the light emanating from one direction that optical axis For flat objects, only diffuse reflections reach the c

Mainly dif reach t Object

Spot light

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❖Lighting Types >> Spot Light

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❖Lighting Types >> Backlight

➢ The backlight principle has the object being illuminated fromcontour or silhouette

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❖Lighting Types >> Backlight

Pros

• Very good contrast

• Robust to texture, color, and ambient light

Cons

• Dimension must be larger than object

Ambient light. Backlight: Enhances contourby creating a silhouette

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❖Lighting Types >> Darkfield

➢ Darkfield means that the object is illuminated at a large angle o

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❖Lighting Types >> Darkfield

Pros

• Good enhancement of scratches, protruding

edges, and dirt on surfaces

Cons

• Mainly works on flat

• Requires small distan

• The object needs to be

Ambient light Darkfield: Enhances relief

ntours, i.e., lights up edge

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❖Lighting Types >> On-Axis Light

➢ When an object needs to be illuminated parallel to the optical a

transparent mirror is used to create an on- axial light source

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❖Lighting Types >> On-Axis Light

Pros

• Very even illumination, not hot spots

• High contrast on materials with different

reflectivity

Cons

• Low intensity req

• Cleaning off semi splitter) often nee

Inside of a can

as seen with ambient light

Ins

as (on

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❖Lighting Types >> Dome Light

➢ The dome light produces the needed uniform light intensity inswalls

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Pros

• Works well on highly reflective

materials

• Uniform illumination, except for the

darker middle of the image No hot

spots

Cons

• Low intensit long exposu

• Dimensions larger than o

• Dark area in the image

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Ambient light On top of the key numbers is a c transparent material causing direct reflections.

The direct reflections are eliminated by the dome light’s even illumination.

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❖Lighting Types >> Laser Light

➢ A 2D camera with a laser line can provide a cost efficient solutand 3D inspections

Pros

• Robust against ambient light

• Allows height measurements (z parallel

to the optical axis).

• Low-cost 3D for simpler applications

Cons

• Laser safety issu

• Data along y is l

• Lower accuracy

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❖Lighting Types >> Laser Light

Ambient light Contract lens containers, the left

is facing up (5mm high at cross) and the right is

facing down (1mm high at minus sign.

The laser line cl height differenc

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❖Lighting Variants and Accessories >> Strobe or Constant

➢ A strobe light is a flashing light

➢ Strobing allows the LED to emit higher light intensity than whaconstant light by turbo charging

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❖Lighting Variants and Accessories >> Diffusor Plate

➢ The diffusor plate converts direct light into diffuse

➢ The purpose of a diffusor plate is to avoid bright spots in the imthe direct light's reflections in glossy surfaces

Two identical white bar lights, with diffuso plate (top) and without (bottom).

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❖Lighting Variants and Accessories >> LED Color

➢ LED lightings come in several colors Most common are red analso LEDs in blue, white, UV, and IR

➢ Different objects reflect different colors A blue object appears reflects the color blue

➢ Therefore, if blue light is used to illuminate a blue object, it wilgray scale image

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❖Lighting Variants and Accessories >> LED Color

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❖Lighting Variants and Accessories >> Optical Filters

➢ An optical filter is a layer in front of the sensor or lens that absowavelengths (colors) or polarizations

➢ Two main optical filter types are used for machine vision:

1

2 Polarization filter: Only transmits light with a certain polarizatipolarization when it is reflected, which allows us to filter out uBand-pass filter: Only transmits light of a certain color, i.e witwavelength interval example, a red filter only lets red through

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❖Lighting Variants and Accessories >> Optical Filters

Original image Image seen by gray

scale camera with ambient light and without filter

Red light and a red band-pass filter

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❑ 2.3 Imaging

➢ The term imaging defines the act of creating an image.

➢ Imaging has several technical names: Acquiring, capturing

➢ To grab a high-quality image → the number one goal for a sucapplication

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❑ 2.3 Imaging

❖Basic Camera Concepts

➢ A simplified camera setup consists of camera, lens, lighting

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❑ 2.3 Imaging

❖Basic Camera Concepts: Digital Imaging

➢ A sensor chip is used to grab a digital image

➢ On the sensor there is an array of lightsensitive pixels

Sensor chip with an array

of light-sensitive pixels.

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❑ 2.3 Imaging

There are two technologies used for digital image sensors:

➢ CCD (Charge-Coupled Device)

➢ CMOS (Complementary Metal Oxide Semiconductor).

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❑ 2.3 Imaging

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❑ 2.3 Imaging

❖Basic Camera Concepts: Lenses and Focal Length

➢ The lens (Objective) focuses the light that enters the camera

creates a sharp image

Focused or sharp image.

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❑ 2.3 Imaging

➢ The angle of view determines how much of the visual scene the

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❑ 2.3 Imaging

➢ The focal length is the distance between the lens and the focal p

➢ When the focal point is on the sensor, the image is in focus

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The spectral response of a sensor is the sensitivity curve for difwavelengths Camera

sensors can have a different spectral response than the human e

Lenses and Focal Length

▪ Focal length is related to angle of view in that a long focal length small angle of view, and vice versa.

Basic Camera Concepts

❑ 2.3 Imaging

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Field of View in 2D

▪ The FOV (Field of View) in 2D systems is the full area that a cam

is specified by its width and height.

▪ The object distance is the distance between the lens and the obBasic Camera Concepts

SICK IVP, “Machine Vision Introduction,” 2006

❑ 2.3 Imaging

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Aperture and F-stop

▪ The aperture is the opening in the lens that controls the amount onto the sensor In quality lenses, the aperture is adjustable.

❑ 2.3 Imaging

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Aperture and F-stop

▪ The size of the aperture is measured by its F-stop value A large

a small aperture opening, and vice versa.

▪ For standard CCTV lenses, the F-stop value is adjustable in the ra and F16.

❑ 2.3 Imaging

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Depth of Field

▪ The minimum object distance (sometimes abbreviated MOD

distance in which the camera lens can focus and maximum obj

farthest distance.

❑ 2.3 Imaging

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Depth of Field

▪ The focal plane is found at the distance where the focus is as sh

▪ Objects closer or farther away than the focal plane can also be co focus This distance interval where good-enough focus is obtaine

ﬁeld (DOF).

❑ 2.3 Imaging

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Depth of Field

❑ 2.3 Imaging

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Depth of Field

▪ The depth of field depends on both the focal length and the apertuBasic Camera Concepts

❑ 2.3 Imaging

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Depth of Field

▪ By adding a distance ring between the camera and the lens, the

thus the MOD) can be moved closer to the camera A distance rin

as shim, spacer, or extension ring.

❑ 2.3 Imaging

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Depth of Field

▪ A side-effect of using a distance ring is that a maximum object

introduced and that the depth of field range decreases.

❑ 2.3 Imaging

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Pixels and Resolution

▪ A pixel is the smallest element in a digital image Normally, the

pixel in the image corresponds directly to the physical pixel on the sensor.

▪ To the right is an example of a very small image with dimension 8x8 pixels The dimensions are called x and y, where x

corresponds to the image columns and y to the rows.

Basic Image Concepts

❑ 2.3 Imaging

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