Vision Basics Lighting I

Vision Basics Lighting I Contrast Backlight Lighting Geometry Effects of Color

Contrast is achieved through proper lighting Creating Contrast CONTRAST It’s all about  CONTRAST A Successful vision application creates optical contrast between the feature of interest and the background Contrast is achieved through proper lighting

Evaluate the Optical Properties Determine what separates the good parts from the bad parts Which optical property or properties can be used to generate CONTRAST ? Color ? Shape ? Texture ? Translucency ? This technique reduces the number of light that must be tested, but does not eliminate testing

Lighting is Very Important What are the most important optical components in any vision application? The PART and the BACKGROUND The Object or Feature of Interest The Background Lighting is used to create this contrast Lighting and Optics are %80 of any vision application!

Lighting is Very Important Keep in mind… Proper lighting creates CONSISTENT contrast Vision tools work better when lighting is repeatable and well controlled In general, software cannot fix lighting problems

Optical Properties What optical properties can be used to create contrast? Color Shape Surface Texture Translucency

Vision Basics Backlight

Backlight Even, diffused light is emitted behind the part Opaque areas = dark (silhouette) Translucent areas = gray Transparent areas = bright Unblocked areas = white

Backlight - Translucency Light transmits differently through section of transparent parts creating contrast between features

Blurry Edges

Method 1 – Block Light Block the light that is causing the problem No light can hit upper surfaces on party

Method 2 – Move Part Move part farther away from Backlight Light can not hit upper surfaces on part

The Solution = Collimation Collimated Light Uncollimated Light Collimated light solves this blurring problem 2 methods to help collimated the light being emitted by a highly diffused backlight Block light Target farther away from Backlight

Close Backlight

Far Backlight

Backlight in the real world Ring Light Lamp Filament Backlight

Backlight in the real world Cap presence and position on a vial

Backlight in the real world Metal pins through a plastic connector

Vision Basics Lighting Geometry θ θ

Lighting is Very Important What type of lights are used to create Geometric affects? Directional Area Linear Array Ring On-Axis Low Angle Ring

Reflection Geometry Light reflects at the angle of incidence Angle of incidence = Angle of reflection θ θ Lighting is a lot like pool; All about angles

Microscopic View of Surface Reflection Geometry If we illuminate this flat shiny surface will the camera see the light? No, the light reflects at the angle of incidence Light reflects away from the camera θ θ Microscopic View of Surface

Microscopic View of Surface Reflection Geometry If we illuminate this rough surface will the camera see the light? Yes, only some light θ θ Microscopic View of Surface

Bright-Field vs Dark-Field Bright-Field Area Dark-Field Area Dark-Field Area FOV

Surface Texture and Geometry Light/Method Smooth surfaces appear… Rough surfaces appear… Directional Bright-Field BRIGHT DARK DARK BRIGHT Directional Dark-Field Low Angle DARK BRIGHT On Axis BRIGHT DARK

Directional Light in the Real World Reduce Glare Same exposure time and gain Only light position changed

Directional Light in the Real World Different surface textures Bright Field vs Dark Field

Directional Light in the Real World Highlight presence and Absence Same exposure time and Gain Only light position changed Cast Shadows

Low Angle Light

Low Angle Light Dark-Field Illumination

Low Angle Light in the Real World Water drops on silicon

Low Angle Light in the Real World Features of a plastic lid

On-Axis Light

On-Axis Light Bright-Field Illumination

On-Axis Light in the Real World Light deflected by presence of solder Light deflected by presence of solder

On-Axis vs Low Angle Lights Opposite Illumination Effects On-Axis light Low Angle light

On-Axis Light in the Real World Laser code on metal shaft

On-Axis Light in the Real World Missing pins in connector

Vision Basics Effects of Color

Color A perception of wavelength

Color – Human Eye Response Three types of cone cells in the eye Each responds differently light’s wavelength

Human Eye Net Response

Imager Chip Responses

Emitted Spectra - Red LED Only red wavelengths present = Red Light

Incandescent Light Bulb All visible wavelengths present = White Light

Vision Basics Two ways to create CONTRAST using color Additive Shine the color of light your are interested in on the part Subtractive Use a filter to remove the wavelengths of light you do not want

Reflected Spectra Incoming white light Reflected red light

Color Wheel Facts to remember about color Reflection A BLUE object appears that color because it reflects BLUE light To make a GREEN object appear bright, shine GREEN light on it Complementary Colors To make a GREEN object appear dark, shine RED light on it (Shine any color other than GREEN)

Color Wheel 3 Color target

Color Wheel Gray scale vision sensor with White light

Color Wheel Gray scale vision sensor with Red light

Color Wheel Gray scale vision sensor with Green light

Color Wheel Gray scale vision sensor with Blue light

Color Lens Filters Filters only let certain wavelengths pass through

Color in the Real World Blue Light Green Light Red Light White Light PCB fiducial application

Color in the Real World Original White Light No Filter Red Filter

Vision Basics Summary

Summary

Summary Optical Properties Shape Surface Texture Color Translucency

Summary What lighting technique can be used to highlight differences in shape Backlight Directional Light (Area Light) Low Angle ight On-Axis light

Summary What lighting technique can be used to highlight differences in surface texture Directional Light (Area Light) Low Angle light On-Axis light

Summary What lighting techniques can be used to highlight differences in color? Color filters and color lights