Vision Basics Lighting II

Vision Basics Lighting II ■ Contrast review ■ IR light ■ UV light ■ Dome light ■ Structured light

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

Evaluate the Optical Properties ? Color ? Shape ? Texture ? Translucency ? ■ Determine what separates the good parts from the bad parts ■ Which optical property or properties can be used to generate CONTRAST 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 IR

IR = Infrared ■ Infrared –Infra = Below –Infrared = Light with a Frequency below red –Longer wavelength than red ■ IR light includes light emitted by –TV remote controls –Heat lamps –Hot objects ■ We are only concerned with Near Infrared (NIR) ■ NIR can act like a different color. –Some objects reflect the light –Some objects absorb the light –Some objects that block visible light may not block NIR

Filters on IR Backlight Visible Light G B R P IR Transparent to IR

Circuit Board on IR Backlight Red backlightIR backlight ■ Same exposure time and Gain ■ Only light position change

Vision Basics UV

UV = Ultraviolet ■ Ultraviolets –Ultra = Above –Ultraviolet = Light with a frequency greater than violet –Shorter wavelength than violet ■ We do not use the reflected UV light from the target ■ We use the light fluorescing from the organic compounds that are stimulated from the UV light ■ The frequency of the UV light can have a large effect on how efficient the organic compound fluoresces

UV Light UV Block Filter UV Light Source UV Band Block Filter Luminance light

Fluorescence UV light strikes certain molecules Calcite crystal (CaCO 3 ) Fluorite crystals (CaF 2 ) Longer wavelength light re-emitted UV Light White Light

Many Fluorescing Colors Possible

Fluorescence in Machine Vision Fluorescing minerals can be added to dyes, glues, …...

IR / UV Summary ■ The effects or IR and UV light on various targets can be surprising ■ Sometimes these lighting techniques can help in generating optical contrast where none existed before

Vision Basics Polarization

■ Light is made up of photons: which are oscillating Electric and Magnetic fields ■ Polarization describes how the electric field oscillates in the plane perpendicular to travel ■ y- z plane in this picture

Polarization States ■ Light can have Linear or Circular Polarization Electric fields oscillating in the plane perpendicular to photon travel

Polarization Method 1 ■ Polarizing filters create a polarization orientation ■ A second filter blocks light or allows or lets light pass through Light Passes Through Light is Blocked

Polarization Method 2 ■ Light reflecting off of non-metallic surfaces at right angles will become polarized ■ The resulting polarized light is parallel to the reflecting surface

Clear Bead on Metal Background Low Exposure TimeHigher Exposure Time ■ Polarized light ■ No Polarizing filter on lens

Clear Bead on Metal Background ■ Polarized light ■ Out-of-phase polarizing filter on lens

Polarization by reflection ■ No change in exposure time or gain ■ Only adjustment between pictures is filter orientation

Polarization by reflection ■ No change in exposure time or gain ■ Only adjustment between pictures is filter orientation

Polarization by reflection ■ Polarization by reflection does not occur in metals ■ A polarizing filter does not reduce glare from metallic surfaces

Polarized Backlight ■ Imperfections in clear materials can randomize the polarization of the light ■ Some plastics randomize polarization but this can be helpful too. Backlight and Lens polarization filters out-of-phase Imperfections show up as bright spots

Polarized Light Summary ■ Non-polarized light can become polarized when reflected off of non-metallic surfaces ■ Polarized light retains polarization state when reflected off of metallic surfaces ■ Polarizing filters can be used to reduce glare ■ Polarized light can be filtered to create contrast

Vision Basics Dome Lighting

Dome Light

■ Light from the Dome Light is scattered toward the part ■ The camera looks down at the part through a hole in the Dome light

Dome Light vs Ambient Light Dome LightDirectional Light

vs On-Axis and Low Angle On-Axis Dome Light Low Angle

Dome Light in the Real World Red LED Ring LightDome Light ■ Metal container

Dome Light in the Real World Red LED Ring LightDome Light ■ Soft drink can

Vision Basics Structured Lighting

Laser Line Generator

Light Plane Laser Light Stripe on Work piece Camera Sees This View

Laser Line with Band Pass Filter No filterWith filter ■ Band pass filter blocks ambient light

Structured Light in the Real World Hex wrenchedCurved surface

Structured Light in the Real World ■ Verify that the proper number of cigars are present

Structured Light in the Real World

■ Monitoring tire rubber thickness

Vision Basics 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