Mašinska vizija. Dr Nenad Jovičić tnt.etf.rs/~mv

Transcription

1 Mašinska vizija Dr Nenad Jovičić tnt.etf.rs/~mv

2 Sadržaj Svetlosni izvori Pregled tehnika osvetljavanja Primeri aplikacija Korišćenje Near IR i Near UV svetlosti Korišćenje optičkih filtara

3 Pristupi u projektovanju osvetljenja Pomeraj i gledaj (najčešći metod) Testiranje sa priručnim osvetljenjem pod različitim uglovima dok se slika prati uživo... Naučni pristup (najefektivniji) iskustvo + znanje + čeklista upućuju na rešenje Korišćenje testnih komponenti (najbrže ali i najskuplje) Isprobati različite profesionalne komponente za osvetljenje u laboratoriji

4 Sve je u kontrastu Uspešno projektovano osvetljenje: Ističe objekte od interesa, tj. povećava kontrast tih objekata u odnosu na okolinu, ili povećava kontrast unutar samih objekata Potiskuje obejkte koji nisu od interesa, tj. umanjuje njihov kontrast (pozadina, šum...) Obezbeđuje minimalnu osetljivost na varijacije usled: Minimalnih razlika od uzorka do uzorka Pristustvo ambijentalnog osvetljenja Pozicije uzorka u ondosu na sistem za snimanje

5 Sve je u kontrastu Uspešno projektovano osvetljenje: Ističe objekte od interesa, tj. povećava kontrast tih objekata u odnosu na okolinu, ili povećava kontrast unutar samih objekata Potiskuje obejkte koji nisu od interesa, tj. umanjuje njihov kontrast (pozadina, šum...) Obezbeđuje minimalnu osetljivost na varijacije usled: Minimalnih razlika od uzorka do uzorka Pristustvo ambijentalnog osvetljenja Pozicije uzorka u ondosu na sistem za snimanje

6 Šta je potrebno znati Znanje o: Prednosti i mane različitih tehnika osvetljenja Spektralne karakteristike senzora (kamere) Primenljivost različitih tehnika osvetljavanja u zavisnosti od karakteristika materijala Zahtevi i ograničenja različitih tehnika osvetljavanja Razumevanje četiri kamena temeljca osvetljenja u viziji: Geometrija Struktura svetlosti Spektar tj. boja svetlosti filtriranje Detaljna analiza: Fizički uslovi u kojima je potrebno primeniti osvetljenje Način na koji intereaguju svetlost i uzorak u konkretnoj aplikaciji

7 Svetlosni izvori Širokopojasni LED - Light Emitting Diode Quartz Halogen Fluorescent Xenon (Strobing) Diskretni (Microscopy) Metal Halide High Pressure Sodium Mercury

8 Relative Intensity (%) Izvori spektar 100 Daytime Sunlight Mercury (Purple) Quartz Halogen / Tungsten 80 Fluorescent Xenon White LED 20 Red LED Wavelength (nm)

9 LED

10 LED - snaga i trajnost

11 Koja je dioda sjajnija?

12 Metal-halide lampe

13 Živine lampe

14 High pressure sodium lampe

15 Poređenje standardnih izvora Type Spectrum Intensity Life (hrs) Comments LED Various Bright to Very Bright Up to 100,000 Long life Stable Output Small Area ** Fluorescent White w/bluegreen, yellow Bright 5000 to 7000 Inexpensive Need High Freq Low Heat Halogen White w/yellow Very Bright 200 to 3000 Inexpensive Xenon White w/blue Very Bright 3000 to 7000 High Heat Expensive Stable

16 Uporedne karakteristike

17 Absolute QE (%) Osetljivost senzora na spektar svetlosti 80 IR Enhanced Analog Digital Interline Transfer Standard Analog CMOS UV Enhanced Analog Human Scotopic (Night-time) Human Photopic IR Block (Short Pass) Wavelength (nm)

18 Interakcija svetlosti i uzorka Total Light In = Reflected + Absorbed + Transmitted + Emitted Light Illumination Absorb Light reflects at the angle of incidence F1 = F2 Reflect Emit Transmit

19 Osnovne tehnike osvetljavanja Partial Bright Field Dark Field Back Lighting Diffuse Dome Axial Diffuse Flat Diffuse Full Bright Field

20 Bright field vs Dark field Typical Co-axial Ring Light Sample Geometry Bright Field Dark Field

21 Dark field vs Bright field Partial Bright Field Lights in White Area Dark Field Lights in Grey Areas Mirrored Surface Scratch

22 Dark field vs Bright field Bright Field Lighting Dark Field Lighting

23 Difuzno DOME osvetljenje Similar to the light on an overcast day. Creates minimal glare.

24 Aksialno difuzno osvetljenje Light directed at beam splitter Used on reflective objects Surface Texture Is Emphasized Angled Elevation Changes Are Darkened

25 Ravno difuzno (flat diffuse) osvetljenje Diffuse sheet directed downward Long WD and larger FOV Hybrid diffuse (dome and coaxial) Coaxial Diffuse Diffuse Flat Diffuse BF Coaxial DF Dome Ring

26 Primer tekst na limenci Purple Ink Concave, reflective surface Axial Bright Dark Diffuse Field Diffuse Illuminator Ring Dome Light

27 Primer tekst na metalu Recessed metal part Reflective, textured, flat or curved surface Bright Bright Dark Field field field Line ring spot light light

28 Primer nalepnica sa celofanom Reading under Cellophane Axial Broad Bright Dark Diffuse Area Field Linear Illuminator Ring Light Array

29 Tehnika u zavisnosti oblika i teksture Surface Reflectivity Flat Matte Mixed Mirror Specular Axial Diffuse Surface Texture / Shape Geometry Independent Area Uneven Topography Bright Field Dark Field Flat Diffuse Diffuse Dome / Cylinder Curved

30 O čemu treba voditi računa Physical Constraints - Access for camera, lens & lighting in 3-D (working volume) - The size and shape of the working volume - Min and max camera, lighting working distance and FOV Part Characteristics - Sample stationary, moving, or indexed? - If moving or indexed, speeds, feeds & expected cycle time? - Strobing? Expected pulse rate, on-time & duty cycle? - Is the part presented consistently in orientation & position? - Any potential for ambient light contamination? Ergonomics and Safety - Man-in-the-loop for operator interaction? - Safety related to strobing or intense lighting applications?

31 Kada šta koristiti Partial Bright Field Dark Field Diffuse Axial Full Bright Field Diffuse Dome Full Bright Field Lighting Type Ring, Spot Angled Ring, Bar Diffuse Box Dome When To -Non specular -Specular / Non -Specular / Non -Specular / Non Use -Area lighting -Surface / Topo -Flat / Textured -Curved surfaces -May be used as -Edges -Angled surfaces -If ambient light a dark field light -Look thru trans- issues parent parts Require ments -No WD limit -Light must be very close to part -Light close to part -Light close to part -Large footprint (limited only to -Large footprint -Large footprint -Camera close to intensity need -Limited spot size -Ambient light minor light on part) -Ambient light may -Beam splitter lowers -Spot size is ½ light interfere light to camera inner diameter

32 Pozadinsko osvetljenje Locates edges Gauging Internal defects in translucent parts Hole-finding Presence / Absence Vision-Guided Robotics: Incl. Pick & Place Useful for translucent materials

33 Pozadinsko osvetljenje Light Diffraction: Bending around obstacles Q D Red D Q Blue Q = l / D, where Q is the diffraction angle and D is opening width High-accuracy gauging: Use monochrome light Shorter wavelengths best Use collimation parallel rays Longer l light penetrates samples better

34 Pozadinsko osvetljenje - primer Small Bottle blue-green Consider colors and materials properties also. Longer wavelength isn t always best for penetration! 660 nm Red Backlight 880 nm IR Backlight 470 nm Blue Backlight

35 Usmereno pozadinsko osvetljenje No Collimation Collimation Film Collimation

36 Pozadinsko osvetljenje u službi preciznih merenja Back lighting Monochrome light better Shorter wavelength a little better Collimation even better Optical collimation better than film Minimal distortion lens Telecentric lens best Measurement calibration CRITICAL* Focus - CRITICAL*

37 Korišćenje boje Use Colored Light to Create Contrast Warm Cool Use Like Colors or Families to Lighten (green light makes green features brighter) R V Use Opposite Colors or Families to Darken (red light makes green features darker) O Y G B

38 Povećavanje kontrasta Warm Cool Red Green O R V B Y G Blue White Consider how color affects both your object and its background! White light will contrast all colors, but may be a contrast compromise.

39 Povećavanje kontrasta Candy pieces are imaged under (a) white light and a color CCD camera, (b) white light and a black and white camera, (c) red light, lightening both the red and yellow and darkening the blue, (d) red and green light, yielding yellow, lightening the yellow more than the red, (e) green light, lightening the green and blue and darkening the red, (f) blue light, lightening the blue and darkening the others.

40 Imaging Beyond Visible Near IR Infra-red (IR) light interacts with sample material properties, often negating color differences. White light B&W Camera IR light B&W Camera

41 Imaging Beyond Visible Near IR Near IR light can penetrate materials more easily because of the longer wavelength. Red 660 nm Back Light IR 880 nm Back Light

42 Imaging Beyond Visible Near UV Near UV light when used w/ a matched UV excitation dye, illuminates codes and structural fibers. Top Image Set: Diaper Lower Image Set: Motor Oil Bottle

43 Ambient Light: Any light, other than the visionspecific lighting that the camera collects. - Overhead plant lighting Ambient Light Mercury, HP Sodium, Fluorescent Tubes - Other nearby task lighting Incandescent, Fluorescent Tubes - Indicator status lights - Temporary lighting construction, emergency - Sunlight Weather and time-dependent - Interference from other nearby vision-specific lighting!

44 Ambient Light Controlling and Negating Ambient Light Turn off the ambient contribution Most effective... Least Likely! Overwhelm the ambient contribution w/ strobing Effective, but requires more cost and complexity Build a shroud Very effective, but time-consuming, bulky and expensive Control it with pass filters Very effective, but requires a narrow-band source light

45 Pass Filters in Machine Vision Pass filters exclude light based on wavelength. 715 nm Long Pass Reduce sunlight and mercury vapor light 4X 510 nm Short Pass 660 nm Band Pass Reduce fluorescent light 35X

46 Pass Filters Top Image: UV light w/ strong Red 660 nm ambient light. Bottom Image: Same UV and Red 660 nm ambient light, with 510 nm Short Pass filter applied.

47 Avoiding Surface Glare Change Geometry 3D spatial arrangement of Light, Sample, and Camera (preferred) Strobe to overwhelm glare from ambient sources Use polarization filters (least preferred) Courtesy Wikimedia Commons

48 Avoiding Surface Glare 3-D Reflection Geometry: Light - Sample - Camera

49 Polarizing Filters in Machine Vision Coaxial Ring Light w/o Polarizers Coaxial Ring Light w/o Polarizers Coaxial Ring Light w/ Polarizers Off-Axis Ring Light w/o Polarizers Coaxial Ring Light w/ Polarizers

50 Polarizing Filters in Machine Vision Back Light - No Polarizer Back Light - No Polarizer Back Light - Crossed Polarizers

51 Polarizing Filters in Machine Vision 6-pack Plastic Ring Carrier Back Light w/o Polarizers Polarized backlighting is best used to detect internal anisotropy in transparent materials. Back Light w/ Polarizers

52 1. Immediate Inspection Physical Environment Physical Constraints Access for camera, lens, and lighting in a 3D space (working volume) The size and shape of the working volume Min and max camera, lighting working distance and fieldofview Part Characteristics Sample stationary, moving, or indexed? If moving or indexed, speeds, feeds, and expected cycle time? Strobing? Expected pulse rate, ontime, and duty cycle? Are there any continuous or shock vibrations? Is the part presented consistently in orientation and position? Any potential for ambient light contamination? Ergonomics and Safety Manintheloop for operator interaction? Safety related to strobing or intense lighting applications?

53 Standard Lighting Method Determine the Exact Features of Interest Analyze Part Access / Presentation Clear or obstructed, Moving / Stationary Min / Max WD range, Sweet Spot FOV, etc. Analyze Surface Characteristics Texture Reflectivity / Specularity Effective Contrast Object vs. background Surface flat, curved, combination Light Types and Applications Techniques Awareness Rings, Domes, Bars, ADIs, Spots, Controllers Bright Field, Diffuse, Dark Field, Back Lighting Determine Cornerstone Issues 3-D Geometry, Structure, Color & Filters Ambient Light Effects / Environmental Issues

54 Summary and Conclusions Develop the lighting solution early on in the vision system process Determine appropriate light geometry techniques Consider reflection geometry Be aware of and block ambient light Consider camera wavelength sensitivity Use monochrome light for high-accuracy gauging Remember that light MAY interact differently w/ respect to surface texture, color and composition Make the lighting solution robust Need more help? Call your lighting professional!!