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Published bySheryl Oliver Modified over 9 years ago
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Vision Basics Lighting II
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Vision Basics Lighting II ■ Contrast review ■ IR light ■ UV light ■ Dome light ■ Structured light
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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
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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
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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!
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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
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Optical Properties What optical properties can be used to create contrast? ■ Color ■ Shape ■ Surface Texture ■ Translucency
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Vision Basics IR
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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
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Filters on IR Backlight Visible Light G B R P IR Transparent to IR
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Circuit Board on IR Backlight Red backlightIR backlight ■ Same exposure time and Gain ■ Only light position change
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Vision Basics UV
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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
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UV Light UV Block Filter UV Light Source UV Band Block Filter Luminance light
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Fluorescence UV light strikes certain molecules Calcite crystal (CaCO 3 ) Fluorite crystals (CaF 2 ) Longer wavelength light re-emitted UV Light White Light
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Many Fluorescing Colors Possible
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Fluorescence in Machine Vision Fluorescing minerals can be added to dyes, glues, …...
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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
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Vision Basics Polarization
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■ 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
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Polarization States ■ Light can have Linear or Circular Polarization Electric fields oscillating in the plane perpendicular to photon travel
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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
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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
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Clear Bead on Metal Background Low Exposure TimeHigher Exposure Time ■ Polarized light ■ No Polarizing filter on lens
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Clear Bead on Metal Background ■ Polarized light ■ Out-of-phase polarizing filter on lens
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Polarization by reflection ■ No change in exposure time or gain ■ Only adjustment between pictures is filter orientation
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Polarization by reflection ■ No change in exposure time or gain ■ Only adjustment between pictures is filter orientation
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Polarization by reflection ■ Polarization by reflection does not occur in metals ■ A polarizing filter does not reduce glare from metallic surfaces
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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
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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
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Vision Basics Dome Lighting
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Dome Light
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■ Light from the Dome Light is scattered toward the part ■ The camera looks down at the part through a hole in the Dome light
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Dome Light vs Ambient Light Dome LightDirectional Light
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vs On-Axis and Low Angle On-Axis Dome Light Low Angle
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Dome Light in the Real World Red LED Ring LightDome Light ■ Metal container
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Dome Light in the Real World Red LED Ring LightDome Light ■ Soft drink can
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Vision Basics Structured Lighting
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Laser Line Generator
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Light Plane Laser Light Stripe on Work piece Camera Sees This View
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Laser Line with Band Pass Filter No filterWith filter ■ Band pass filter blocks ambient light
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Structured Light in the Real World Hex wrenchedCurved surface
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Structured Light in the Real World ■ Verify that the proper number of cigars are present
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Structured Light in the Real World
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■ Monitoring tire rubber thickness
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Vision Basics Summary
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Optical Properties ■ Shape ■ Surface Texture ■ Color ■ Translucency
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Summary What lighting technique can be used to highlight differences in shape ■ Backlight ■ Directional Light (Area Light) ■ Low Angle ight ■ On-Axis light
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Summary What lighting technique can be used to highlight differences in surface texture ■ Directional Light (Area Light) ■ Low Angle light ■ On-Axis light
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Summary What lighting techniques can be used to highlight differences in color? ■ Color filters and color lights
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