multispectral imaging: more than just a picture hyperspectral imaging ... •single, dual, and multi...
TRANSCRIPT
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Multispectral Imaging: More Than Just A Picture
Ray LeerentveldDirector of Product Management
Lumenera Corporation
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Presentation Outline
• What is multispectral imaging (MSI)?• How does it differ from hyperspectral imaging?
• MSI acquisition
• Recent advancements in multispectral technology
• Multispectral Imaging Techniques
• Multispectral applications:• Case Study on Normalized Difference Vegetation Index
• Food Inspection
• Textile Inspection And Analysis
• Printed Circuit Boards
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What Is Multispectral Imaging?
• Multispectral imaging involves breaking the light spectrum into multiple bands beyond the basic RED, Green and Blue
• Multispectral can run beyond the visible spectrum into Ultra Violet or out to Infra Red
Content Courtesy of Midwest Optical Systems
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What Is Multispectral Imaging?
• Multispectral imaging is a subset of Hyperspectral imaging typically seen as 2 to 32 segmented bands
• Hyperspectral can have a hundred or more bands
Multispectral Hyperspectral
Content Courtesy of Midwest Optical Systems
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Multispectral Vs. Hyperspectral Imaging
• Multispectral can often be represented with a single false-colored image to provide quick visual representation of the data
• Hyperspectral utilizes a three dimensional dataset known as a hypercube that requires 3D analysis to determine the spectral data of interest
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Multispectral Image Acquisition
• Multispectral image acquisition can be accomplished using:• Wafer-level coated sensors
• Lighting with varying wavelengths
• Multispectral Camera
• Specialized Filters (Multi-Camera) or Filter Wheels
Content Courtesy of Delta Optical Thin Film and Glana
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Multispectral Imaging Acquisition – Sensors
• A variety of coatings can be applied directly on the wafer in arbitrary patterns to suit a specific application’s needs
• Pixel level ----RGB+NIR
• Area ------------Mosaic of squares at different wavelengths
• Pros: Can be used on small sensors, highly customizable, built into the sensor, easy to integrate into cameras
• Cons: Expensive in small volume, strong side bands, and limited spectral complexity
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Multispectral Imaging Acquisition – Lighting
• The subject can be illuminated with varying wavelengths of light and images captured with a monochrome camera
• Pros: Lower cost and higher resolution
• Cons: Static subject, limited to diversity of light wavelengths, requires controlled environment
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Multispectral Imaging Acquisition – Camera
• Cameras with special gratings & sensors can be used for MSI
• Pros: accurate and purpose-built
• Cons: large, low sensitivity: ~25µm entrance slit, and expensive
Content Courtesy of Delta Optical Thin Film and Glana
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Multispectral Imaging Acquisition – Filters
• A number of filter setups exist to achieve multispectral imaging:• Rotating filter wheel
• Pros: Large number of filters available, high resolution, and lower cost
• Cons: Static Subject, large filter wheel assembly
• Single, dual, and multi bandpass filters using multiple cameras• Pros: Application-specific filters, high resolution, and lower cost
• Cons: Quantity of Cameras required proportional to wavelengths
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Recent Advancements In Multispectral Tech
• Delta Optical Thin Film’s continuously-variable sensor-mount hyperspectral filter
• Bandwidths and frequency range are customizable
• Turns a high-resolution 35mm format camera into a hyperspectral system
• Spectral resolution directly proportional to spatial resolution
Content Courtesy of Delta Optical Thin Film and Glana
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Multispectral Imaging Techniques
• Step and Stare • Subject must be static
• Snapshot then cycle filter/lighting/etc
• Push Broom/Panning• Subject/camera must be moving linearly
• Sequence of images are stitched together to form hypercube
Spectral Results
Panning IllustrationContent Courtesy of Delta Optical Thin Film and Glana
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Camera Solution Filter Versus Grating
• Shorter optical path smaller solution
• More light reaches the sensor
• 3D hyperspectral imaging possible due
to linear camera panning
• Image stacking in the cube can be easily
accomplished due to high spatial
resolution
Content Courtesy of Delta Optical Thin Film and Glana
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Why Is Multispectral Imaging Important?
• See more than the naked eye: See beyond color
• The evolution of imaging MonoColor3DMultispectral
• A wide range of industries benefit from multispectral imaging
False-color representation of a hypercubeContent Courtesy of Delta Optical Thin Film and Glana
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Case Study
An Example of Multispectral Customization
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Example Of Multispectral Customization
• Normalized Difference Vegetation Index (NDVI)
• Started with multispectral satellite imaging
• Applied the technology to a multi-camera earth-based solution
• Evolved to a single camera solution
• Takes advantage of an existing, well defined technology and applying it to a custom solution
Cost
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Normalized Difference Vegetation Index (NDVI)
• NDVI is a popular index to measure healthy vegetation using satellite imagery
• Normalized between -1 and +1• Healthy vegetation ranges from 0.2 to 0.8
• Plants absorb red light through photosynthesis and reflect NIR light
• NDVI Equation: 𝑁𝐷𝑉𝐼 =𝑁𝐼𝑅 − 𝑅𝑒𝑑
𝑁𝐼𝑅 + 𝑅𝑒𝑑
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Vegetation Spectral Response
• Review Hyperspectralresponse to select targeted Multispectral bands
• Healthy plants absorb blue and red, reflect green and highly reflect NIR
• Single color camera with dual bandpass filter can be used to approximate NDVI
Content Courtesy of: “Low-cost multispectral vegetation
imaging system for detecting leaking CO2 gas”
Applied Optics. 51, A59-A66 (2012)
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Single Camera NDVI
• A pseudo-NDVI camera is created by placing a dual bandpass filter in front of a color camera
Content Courtesy of Midwest Optical Systems
𝑁𝐷𝑉𝐼 =2 × 𝑅𝑒𝑑 − 𝐵𝑙𝑢𝑒
𝐵𝑙𝑢𝑒
*Green channel not used
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Single Camera NDVI
• Can be applied to food inspection to search for inorganic contamination or detecting unhealthy produce
NDVI Approximation Using Lumenera’s Lt965C and MidOpt’s DB475/850
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Food Inspection
• Human inspection is predominant
• Since the early 2000s there has been a significant uptick in research surrounding multispectral food inspection
• Main areas of research include:• Fruit – Damage & disease detection
• Vegetables – Damage & shelf life determination
• Meat – Bacteria detection & marbling quality
• Seafood – Determine expiry & gelatin adulteration
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Food Inspection – Light Penetration In Fruit
• Differing wavelengths will penetrate fruit at various depths for example in an apple
• 4mm between 700 and 900 nm
• 2 to 3 mm between 900 and 1,900 nm
• Multispectral imaging can analyze structures beneath the surface of fruit, helping to detect damage and disease
• Reference libraries can then be created to catalog and reference good vs bad produce or a specific property
• Red color of Cranberries related to the anthocyanin concentration, an antioxidant
directly related to ripeness and value
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Textile Inspection – Matching Of Materials
• Multispectral cameras can image textiles with more color accuracy
• Samples can be accurately reproduced• Various parts of a garment can be accurately color matched
• Leather, vinyl, plastic, thread, metal, polyester spectral match to fabric
• Specific tint reproduction can be conserved and exchanged
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Printed Circuit Board Inspection
• Typically inspected with RGB & IR for thermal functionality
• Large variety of components makes inspection challenging & time consuming
• Component and precious metal detection is essential for recycling
• Multispectral imaging can image buried copper
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PCB Inspection – VIS Vs. NIR
VISNIR
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PCB Inspection – VIS Vs. NIR
VIS NIR
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Summary
• New filter technologies offer many approaches to MSI• Lower Cost
• Highly Customizable
• High Spatial and Spectral Resolution
• There are a number of ways to customize MSI using:• Filters
• Cameras
• Sensors
• Lighting
• Many applications can benefit from MSI:• Food Safety/Inspection
• PCB Inspection
• Textile Inspection
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Acknowledgements
• Supplemental Content Providers
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Contact Information
Ray LeerentveldDirector of Product Management
Lumenera Corporation7 Capella Court
Ottawa, Ontario
Canada
Telephone: +1 613 736-4077
Email: [email protected]
www.lumenera.com
Booth: 2662