Enhance Your Vision Applications with Optical Filtering

Enhance Your Vision Applications with Optical Filtering

Jason Dougherty Managing Director Midwest Optical Systems

Agenda Why should you use optical filters? Optimize your lighting with optical filters Additional benefits and features of optical filters Things to consider when choosing filters Application examples Q & A 3 2013 Cognex Corporation

How to think about filters Oftentimes optical filters are viewed as an afterthought Optical filters are a necessity not an accessory Filter Lens Camera Light Filter Lens Light Camera 4 2013 Cognex Corporation

Optical filtering in action 5 2013 Cognex Corporation

Why should you use optical filters?

Why optical filters? Control quality and quantity of light Block all unwanted ambient lighting Pass only the output of lighting used for inspection Increase contrast and resolution 7 2013 Cognex Corporation

Increase contrast and resolution A lens with Chromatic Aberration doesn't focus all wavelengths of light to a single point resulting in less than optimal images. White Light Lens No Bandpass Filter Multiple Focal Points White Light Bandpass Filter Single Focal Point Before Bandpass Filter After Bandpass Filter 8 2013 Cognex Corporation

How filters control light Digital Camera Spectral Response Interfering Light Reaching the Application Bandpass Filters Block Interfering LIght 9 2013 Cognex Corporation

How filters can increase contrast Pass Light = Highlight Color Selectively pass or block light wavelengths which can highlight or darken areas of an image Block Light = Darken Color Pass Light With Green Bandpass Filter And Highlight Green Colored Marker Blocked Wavelengths With Green Bandpass Filter Darken Blocked Colors 10 2013 Cognex Corporation

Does filter quality matter? Filters designed for photographic film are not suitable for digital imaging systems! Color Image, No Filter Green Photographic Filter Red Photographic Filter 11 2013 Cognex Corporation

And here s why Relative Spectral Response CCD/CMOS Photographic Film Relative Spectral Response: Film vs Digital Camera Photographic Filters Limit Transmission When Used with a Digital Camera Sharpcut / Longpass Filters Are Suitable for Photography But Not Machine Vision Machine Vision Filters Isolate the Desired Wavelengths 12 2013 Cognex Corporation

MV filters optimize image quality Camera, No Filter Photographic Filter Machine Vision Green Bandpass Filter 13 2013 Cognex Corporation

Optimize your lighting with optical filters

Monochromatic LED lighting Monochromatic (single color) LED lighting is most commonly used for illumination in applications to isolate the desired wavelength 15 2013 Cognex Corporation

Designed for modern day illumination Designed for High Transmission All machine vision bandpass filters should have an antireflective coating to increase transmission More light = faster speeds and added efficiency Allows LED to operate with less intensity Maximize output and increase lifespan of the LED which results in less light intensity on the factory floor Mimic the output of the LED 100% - - - 75% - - - 50% - - - 25% - - - 0% 16 2013 Cognex Corporation

Designed for modern day illumination Typical monochromatic LEDs have a total light output of 60-70+/-10nm filters are designed purposefully broad to accommodate the entire output of the LED Solid Blue 470 LED Spans 60-70 nm Acutely Narrow Filter Spans 20 nm Bandpass Filter Spans 80-90 nm Narrow Bandpass Filter Spans 40-50 nm 17 2013 Cognex Corporation

White light Made up of the entire visible spectrum = = White LED Visible Light Spectral curve of a white LED shown spanning the entire spectrum 18 2013 Cognex Corporation

Test white light and bandpass filters = White LED no filter, no contrast = Blue LED highlights push pin = Blue Bandpass Filter highlights blue push pin 19 2013 Cognex Corporation

Additional benefits and features of optical filters

Protect your lens investment Filters protect the surface of the lens and internal threads from dust, scratching, cleaning and inhospitable environments Safe Lens Broken Filter 21 2013 Cognex Corporation

Save money and space Optical filters can eliminate light shields 22 2013 Cognex Corporation

Camera resolution flexibility A filter improves contrast significantly making it possible to get acceptable detection results using a lower resolution camera High Resolution Camera Orange Fluorescent Spot Detected In The Application Low Resolution Camera With Orange Bandpass Filter 23 2013 Cognex Corporation

Extreme durability 24 2013 Cognex Corporation

Insures repeatability and stability Filters create a low-cost Insurance Policy for the lifetime of the application Image Lab Consistent Lighting Environment Achieve consistent results with Optical Filters Factory Floor Inconsistent Lighting Environment 25 2013 Cognex Corporation

Things to consider when choosing a filter Define Imaging Objective Light & Wavelength Monochrome or Color Camera Filter Mount Size

Define imaging objective Define Imaging Objective Low Contrast Interfering Ambient Light Reduce Light Intensity Color Sorting Edge Detection Reduce Glare Remove Barcode Interference Camera Bloom Overpowering Light Source 27 2013 Cognex Corporation

What s your optimal LED wavelength? Light & Wavelength Utilize white light with bandpass filters to test & determine the optimal LED wavelength for your application Original Color Image Blue Bandpass / UV Block Light Green Bandpass Orange Bandpass Light Red Bandpass IR Bandpass 28 2013 Cognex Corporation

How do you find the right filter? Light & Wavelength Filter Test Kits Find the most suitable wavelength to optimize image quality Test before investing In hardware Find the most suitable match for the light source Find the best filter to maximize contrast Find the best filter to control interfering light 29 2013 Cognex Corporation

Monochrome or color? Monochrome or Color Camera A Bayer filter array runs over a monochrome sensor Analyzes each pixel s color information and, combined with that of adjacent pixels, recreates the full color image Resolution loss is most pronounced when detection of a single or a few colors is all that is required 25% Red Pixel RGB sensor 50% Green Pixel 25% Blue Pixel 30 2013 Cognex Corporation

Monochromatic imaging Monochrome or Color Camera Significantly increase camera efficiency Color Monochrome Monochrome with Filter Blue Bandpass Filter 25% Efficient 90% Efficient Entire sensor is used to detect intensity. Original Color Image, UV 395nm LED No Filter Blue Bandpass Filter Combined with a blue bandpass filter that transmits 90+%, a monochrome sensor vs a color sensor is at least 3 times more efficient 31 2013 Cognex Corporation

Mount to any system Filter Mount Size 32 2013 Cognex Corporation

Application examples

Date/lot code reading Challenge: Low contrast between yellow background and white letters White Text Yellow Background Solution: Blue bandpass filter Why does it work?: Blue bandpass filter blocks yellow reflection, darkening background White LED, Blue Bandpass 34 2013 Cognex Corporation

2-D code reading Challenge: Reading 2-D codes with ambient light changes on a curved metal surface Red LED, No Filter Solution: Red bandpass filter Why does it work?: Only pass illumination from system, block overhead lighting Red LED, Red Bandpass Filter 35 2013 Cognex Corporation

Color sorting/counting Challenge: Low contrast between two colors Solution: Blue or red bandpass filter Original Color Image Why does it work?: Red bandpass filter highlights red, blue highlights blue Monochrome, No Filter 36 2013 Cognex Corporation

Color sorting results No Filter No Filter Blue Bandpass Filter Red Bandpass Filter 37 2013 Cognex Corporation

Reading exterior barcodes Challenge: Overcome interference from barcode s background No Filter Solution: Infrared (IR) bandpass filter Why does it work? The ink on the beverage label reflects IR IR Bandpass Filter IR PASS 38 2013 Cognex Corporation

Finding the fabric edge Challenge: Very low contrast between two colors Solution: IR bandpass filter creates the effect of using an IR camera No Filter IR Bandpass Filter Why does it work? Material on left reflects IR, material on right absorbs IR IR PASS 39 2013 Cognex Corporation

Reducing saturation Challenge: Reduce excess IR emitted through heat in the production process No Filter Solution: Shortpass filter Why does it work? Shortpass filters block IR light generated from heat IR/Red Block Visible Pass Filter IR Block 40 2013 Cognex Corporation

Counting LEDs Challenge: Over saturation of light on the part being inspected Solution: Neutral density filter Iris Set To Smallest Aperture To F/16, No Filter Why does it work? Filter evenly decreases overall light transmission Iris Set To Smallest Aperture To F/16, With 1% Transmission) Neutral Density Filter IR Block 41 2013 Cognex Corporation

Verifying presence of sockets Challenge: Overcome specular glare on exterior packaging Solution: Polarizer on filter and lens No Filter Specular Glare Why does it work? Reduces specular reflections by cross aligning polarizers for maximum extinction Linear Polarizer For Lens & Linear Polarizer Film For Light Source 42 2013 Cognex Corporation

Fluorescence and optical filters Excitation light source (395nm LED) Emission from object (Light blue fluorescence) 43 2013 Cognex Corporation

Fluorescence in action No Filter, 395nm UV Light 395nm UV Light With Blue Bandpass Filter Excitation light source (395nmLED) Emission from object (Light blue fluorescence) Excitation light source (395nmLED) Emission from object (Light blue fluorescence) Blue Bandpass Filter 44 2013 Cognex Corporation

The bottom line Of all the available tools to control what a camera sees, optical filters are: The simplest The quickest The most cost effective way To improve repeatability and stability in any machine vision system! 45 2013 Cognex Corporation

Thank you!