The Fundamentals Of Camera And Image Sensor Technology
The Fundamentals ofCamera and ImageSensor TechnologyJon ChouinardSales Manager, Eastern RegionBaumer Ltd.
Digital Cameras: Basic Course Light Basics CCD/CMOS Imager FundamentalsDigital Camera PrincipalsInterfacesCamera Types and When to Use
Digital Cameras: Basic Course Light and CCD/CMOS Sensor Fundamentals Light Basics CCD and CMOS Sensors Digital Camera Principals Camera Interface Standards Camera Types and When to Use
Light BasicsElectromagnetic SpectrumLight is a very narrow band in the electromagnetic spectrum
Light BasicsLight SpectrumWe are primarily interested in wavelengths from 200–1100 nm– Visible Light:– NUV:– NIR:400 – 750 nm200 – 400 nm750 – 1100 nm
Light BasicsLight is represented as botha particle and an electromagnetic wave A light particle is called a photon.Photons have some energy. (UV - IR)The amount of energy determines the wavelength.The wavelength corresponds to a color.Intensity of light number of photons.E Energy of Photonh Planck's constantc Speed of light Wavelength of Light
Light BasicsPhotoelectric Effect: Photons to Electrons Light photons hitting a Siliconsurface will dislodge electrons Number of electrons releaseddepends on intensity andwavelengthSilicon ( )
Light BasicsQuantum Efficiency (QE):The ratio of light that the sensor converts into charge. 60% QE For every 10photons hitting a pixel, 6electrons are released. QE response is sensorspecific. Camera designdoes not affect the QEcurve. QE is given in eitherabsolute or relativeterms. Relative QE is notgood for comparison.
Light BasicsThe Full Well Capacity is the maximum number ofelectrons that register a signal in a pixel. Largerpixels have higher well capacity which also leads tohigher sensitivity, better Signal to Noise Ratio(SNR), and increased dynamic range.Full Well Capacity:4,000 electrons – Small pixels10,000 electrons – Medium pixels50,000 electrons – Large pixels
Digital Cameras: Basic Course Light and CCD/CMOS Sensor Fundamentals Light Basics CCD and CMOS Sensors Digital Camera Principals Interfaces Camera Types and When to Use
CCD and CMOS SensorsThe main difference between CCD and CMOS is howthey transfer the charge out of the pixel and into thecamera’s electronics “Read Out”.CCDCMOSVoltageSampleCurrentPixel:Read Out Circuitry:
CCD and CMOS SensorsCCD SensorThink “Bucket Brigade!”
CCD and CMOS SensorsCCD Sensor “Charge-Coupled Device” CCD imagers are CurrentDriven Devices Charge is collected in pixels The charge is then physicallyshifted on the imager surfaceto the output for sampling The CCD output is an analogpulse where the charge isproportional to the lightintensity
CCD SensorMicrolens Microlenses increase the photoncollection area of the pixel and focus thephotons into the photosensitive area(Good “Fill Factor” ) Almost all modern CCD designs usemicrolenses (Color & Monochrome ) PRO - Effectively increases the quantumefficiency of the pixelCCD Pixel with microlens CON – Creates and angular sensitivity tothe incident light ray
CCD and CMOS SensorsMicrolenses decrease sensitivity to angular raysCCD focalplaneLensCenter raysPeripheralraysPixelsAngle tooptical axisOptical axisAngular QE data for Kodak KAI 0340 CCDVaries due to the photosensitive areanot being square!
CCD and CMOS SensorsCCD Imager Horizontal lines are shifted down thesensor. Pixels are read out from ahorizontal shift register through acommon circuit Main Advantage: Sensitivity, CMOS is surpassing Fidelity Main Disadvantage SpeedPixel OutHorizontal Shift-Register*CCD: Charge-Coupled Device
CCD and CMOS SensorsCCD Issues: Blooming Blooming is known as the spread of charges toadjacent pixels due to over saturation of pixels. This makes some very bright spots in the image.
CCD and CMOS SensorsCCD Issues: Smearing Smear is similar to blooming. It’s caused by pixelsbecoming saturated, and light spilling over into thevertical shift register while clocking out
CCD and CMOS SensorsCMOS Sensor “Complimentary Metal-Oxide Semiconductor” CMOS imagers are Voltage Driven Devices Light striking the pixel creates a voltageproportional to intensity The voltage is sampled directly at the pixel,digitized on the imager and cleared for thenext frame (picture) The CMOS imager has a completely digitaloutput
CCD and CMOS SensorsCMOS Issues: Pattern Noise Sensitivity CMOS layer stack up prevents using microlens and has lower charge conversionthan CCD, usually resulting in lower sensitivity. Higher Image non uniformities (aka “Fixed Pattern Noise“) due to unevennessbetween the individual Pixel cells and multiple A/D circuits in column readout. CMOS is more resistant to Smearing or Blooming than a CCD!
CCD and CMOS SensorsCMOS SensorVoltage sampling is faster than rolling charge in CCD. This makes readout faster than CCD Less flow of charge Less powerMain Advantages:Speed Power ConsumptionSensitivity in newer sensorsMain Disadvantages:Pattern NoiseSensitivity (older sensors)
CCD and CMOS SensorsCMOS Issues: Rolling Shutter An electronic shutter (CCD) or global shutter (CMOS) allow exposure of the whole frame atthe same time. A rolling shutter will expose the frame line after line. The number of exposures equals thenumber of lines in the frame.Image taken with global shutterImage taken with rolling shutter
CCD and CMOS SensorsCMOS Issues: Rolling Shuttereffective integration timeend of integration1st row of AOIH2nd row of AOIH3.8µs@ 40MHzFlash-Windowstart of integrationlast row of AOIHtime of flashtotal running timeA strobe can be used to help freeze the motion and minimizerolling shutter effects
CCD and CMOS SensorsCMOS Issues: Rolling ShutterMoveMoveImage example with a moving object taken with globalshutter.Image example showing distortion caused by a rollingshutterDistorting caused by a rolling shutterPicture taken from a moving car. The railing in front has verticalbars. Note that the vertical bars are shown distorted caused bythe rolling shutter. The actual shutter setting is short enoughto freeze the movement.
CCD and CMOS SensorsProgressive and Interlaced Scanning Image from camera is formed by sequence of pixel lines scannedand displayed in one of two different ways. Progressive scanning : Scanning of first line, second line, third line, etc until the entire frameis scanned. Interlaced scanning : Scanning of odd-numbered lines, then scanning of even-numberedlines. Both fields are then combined to form the entire frame. Found in analog cameras
CCD and CMOS SensorsInterlaced Scan (NTSC,RS-170,PAL,CCIR)1 Frame 2 Fields24681012Field 215Interlaced scan is used in normal TVsystems. Odd lines (1-3-5.) are scanned infirst field. In second field, even lines (2-46.) are scanned. One full frame consist of2 interlaced fields (2:1 interlacing).7The benefit is smoother motion whendisplayed on a monitor.3911Field 1The drawback is that each field has aseparate exposure. The 2 exposures in oneframe cause fast moving objects to blur;interlace blurring.
CCD and CMOS SensorsInterlace Blurring
CCD and CMOS SensorsProgressive Scan (Non-interlaced)1 Frame 1 Field1234567891011Non-interlaced scan or progressivescan is used in machine vision. Thelines are scanned progressive fromtop to bottom in one full frame.The scanning system is a nonstandard. The video can not beshown on a standard CCTV monitor.The benefit is that a full frame isavailable as the result of a singleshutter event.
CCD and CMOS SensorsProgressive and Interlaced scanning
CCD and CMOS SensorsProgressive and Interlaced scanning Interlaced scanning: Spatial resolution is reduced but temporal resolution is improved. Twice as many‘full’ images are presented per second. Progressive scanning: Sharper images are formed No interlaced blurring!Note: With interlaced, you’ll see smoother motion with same framerate, but will also notice the interlaced lines in the image.
CCD and CMOS SensorsImage Format1”TubeDeflectionyokeDiagonal:The image size in inches relates back to the tubecamera. The image format of a tube which could beplaced in a 1” deflection coil was called 1” format. Theactive image size is 16 mm in diagonal. It is the sameas for a 16 mm film format.Below is the most common image formats shown.1” format2/3” format1/2” format1/3” formatType 1Type 2/3Type 1/2Type 1/316 mm11 mm8 mmImagesize12.8 mm8.8 mm6.4 mm6 mm4.4 mm
CCD and CMOS SensorsImage FormatLens specs must match image format. 1/3” Sensor Format ideally should be paired with 1/3” format lens Larger format lens can be used on smaller sensor Smaller format lens can NOT be used on larger sensorBadGoodOK
CCD and CMOS SensorsLens Mount - C-mount and CS-mountLens threadFocalplaneLens flangeFlange back distanceC-mount 17.526 mmCS-mount 12.526 mmTIP - With a 5 mm adapter ring, a Cmount lens can be used on a CSmount camera.The most common lens for CCTV cameras are ofthe C-mount or CS-mount type.The lens thread and the distance from the lensreference flange to the image plane is standard.The lens thread is 1-32 UN-2A.Diameter is 1 inch.The flange back distance in air is 17.526 mm forC-mount. For CS-mount it is 12.526 mm.Glass filters or prism between lens and focalplane will increase the distance.
Summary / Tips CCD: High image fidelity, lower speed. CMOS: High speed, lower image quality. Don’t use Rolling shutter for motion.
Digital Cameras: Basic Course Light and CCD/CMOS Sensor Fundamentals Concept of the Digital Camera Analog and Digital Concepts in Imaging Digital Camera Benefits Image Quality Basics Camera Controls and Their Effects Interface Comparison Camera Types and When to Use
Analog and Digital Concepts Charges from the pixels must be converted first to a voltage. This is donewith a capacitor circuit Then the voltage levels must be measured and converted to a number.This is done with the analog to digital converter (A/D) Along the way, Gain and Offset can be adjusted before the conversiongain & offsetA/DA/Dgain & offset
Analog and Digital ConceptsThe A/D Converter will represent voltage levels as Binary Numbers and convert to digital!Binary Counting vs. Decimal: A pixel is given a number value based on amount of light itreceivesCameras use binary numbers to represent the amount of lightHumans (and cameras) use decimal numbers which representsa grey scaleThe more bits you use, the higher you can count!
Analog and Digital ConceptsSo with more bits, you have more valuesto represent the light intensity from black to white.This is called “Bit Depth.” ( 2 8 256 )8 bit image256 pixelvaluesavailable4 bit image16 pixelvaluesavailable1 bit image2 pixel valuesavailable
Analog and Digital ConceptsHigh Bit Depth Considerations With more bits, you get a more accuratemeasurement of the light. (8, 10, 12 bits 256, 1024,4096 grey scales) With more bits, you also have more data to transfer,process, store (12 bit 50% more data more than 8bit).
Digital Cameras: Basic Course Light and CCD/CMOS Sensor Fundamentals Concept of the Digital Camera Analog and Digital Concepts in Imaging Digital Camera Benefits Image Quality Basics Camera Controls and Their Effects Interface Comparison Camera Types and When to Use
Digital Camera BenefitsGoal of Digital Cameras: To Replace Analog CamerasDigital cameras use the same sensors asanalog camerasDigital CameraµCconfig.SensorSensorAnalog Ca meraADCI/O So, there is no difference in image quality at thesensor level, BUT.
Digital Camera BenefitsNo Frame Grabber required with Digital!Frame GrabberSensorAnalog Cameraconfig.PCµCADCFlashTriggerPCII/OAnalog problems: Pixel jitter Noise EMI Susceptibility Settings via dipswitchOverall Image Quality is Better with Digital!Digital CameraSensorµC PC AdapterPCIADCI/OPowerFlashTriggerPCDigital Solutions: Exact pixel readout No losses on the cable Settings via software
Digital Camera BenefitsAnalog DigitalCCIR / PAL 624 lines, 25 fpsEIA / NTSC 525 lines, 30 fpsProprietary more linesInterlaced / progessive scan640x480 @ 30 - 250 fps1392x1040 @ 20 - 60 fpsOr Choose your own frame rateOr choose your own resolution,region of interest (ROI) Progressive Scan Why Digital? Much more flexible Natural choice for high resolutions
Digital Camera BenefitsAnalog Composite 1 wire - cross talk S-VHS 2 signal wires RGB 3 or 4 signal wiresDigital RGBYUV 4:2:2Mono8 / Mono16Raw Bayer (Color) ouput Use your own interpolation
Digital Camera BenefitsDigital cameras can provide advanced features Test Image Time Stamp Frame Counter I/O Port Status Error Checking Partial Scan Image Flip
Digital Camera BenefitsDigital cameras can do on-board processingExample: High Dyanmic Range Images (HDR)Other examples: Blemish Compenstion, Flat Field Correction(FFC), Multi-ROI
Digital Cameras: Basic Course Light and CCD/CMOS Sensor Fundamentals Concept of the Digital Camera Analog and Digital Concepts in Imaging Digital Camera Benefits Image Quality Basics Camera Controls and Their Effects Interface Comparison Camera Types and When to Use
Image Quality BasicsTemporal Noise: Anything besides light that causes a pixel’s value tochange over time (temperature, ADC errors, etc.).This is measured by EMVA 1288Spatial Noise: “Fixed Pattern Noise.” Constant non-uniformities inthe image caused by bad sensor design, electricalnoise, etc.
Image Quality BasicsSome Sources of Temporal Noise: Shot Noise / Photon Noise:Due to random fluctuations in the light.[Brighter/Better Light less shot noise] Dark Current Noise:The rate at which electrons are produced due tothermal effects. Every 8 C Dark noise doubles.[cooler camera less dark noise] Quantization Noise:Errors coming from the A/D conversion process[Use a better ADC less quantization noise]
Image Quality BasicsSome Sources of Spatial Noise (Fixed Pattern): Bad sensor design EMI
Image Quality BasicsSignal To Noise Ratio (SNR): The ratio of good signal caused by light to unwantednoise. The most important measurement of imagequality for digital cameras.SNR Tips: High SNR achieved with largewell depth (lots of signal todrown out the noise)Signal electronsfrom light Good camera design requireless light to overcomeNoise electronsfrom heat, spatal,temporal, etc.
Image Quality BasicsSignal to Noise Ratio (SNR) SNR Curve Characterization: At-a-glance indicator of image quality andperformance. Each camera has it’s own and is unique.Saturation:well is full!Higher SNR!(S/N)Noise floor:point whereSignal NoiseMORE LIGHT!Dynamic Range“Good” ImageQuality“Acceptable”Image Quality
Image Quality Basics- Use the SNR Curves of various camerasto compare performance.- A camera good in low light is not alwaysthe best in bright light!!- Know before you buy!
Image Quality BasicsDynamic Range: The measure of how well a camera canrepresent details when both bright and dark areas arepresent.Capture Methods Sensor algorithms(clips) Multi-Exposure Higher bit depthLowHigh
Image Quality BasicsEMVA1288: Industry standard for measuring image quality ofdigital cameras. Testing uses known set of conditions (light, lens, targets, etc.). Manufacturers’ report data in agreed-upon format. Results for multiple cameras published to show level ofconsistency. Allows customer to compare apples to apples. http://www.standard1288.org/
Digital Cameras: Basic Course Light and CCD/CMOS Sensor Fundamentals Concept of the Digital Camera Analog and Digital Concepts in ImagingDigital Camera BenefitsImage Quality BasicsCamera Controls and Their Effects Interface Comparison Camera Types and When to Use
Camera ControlsWhat are some camera controls can we use to affectimage quality? GainExposureBrightness (black level)Image FormatResolution (Array Size)
Camera ControlsGain: Amplifies analog signal from pixel before conversion.– Pro: Higher Grey Scale level (Brighter)– Con: Noise introduced (6db gain 2X increase)
Camera ControlsGain Considerations: Increasing gain will increase visibility of both signaland noise! Does not increase image quality! Use only as a last resort to increase brightness. Gain may be limited at higher bit depths.
Camera ControlsExample Images of Gain Effects:High Gain used to compensate for low light.Bright image, but noise is apparentLow gain and good lighting is used. Lightdrowns out noise and makes clean image.
Camera ControlsExposure Time: The length of time that the sensor isopen for collecting light. Also known as shutter speedand integration time.Exposure Time Considerations: Frame rate may be reduced with increase. Motion blur is greater with increase. SNR is greatly increased with more exposure (longershutter time – filling pixel well)
Camera ControlsExample Images of Exposure Effects:Underexposed image: Detail lost in shadowsGood image: Detail is visibleNote that “Good” and “Better”are always a matter of opinionand application. Contrast is King!Better image: Good detail and good contrastOverexposed Image: Detail lost in highlights
Camera ControlsBlack Level (Brightness): Adds an offset to pixel values.Adjusting the camera’s black level will result in an offset to thepixel values output by the camera. Increasing the black levelsetting will result in a positive offset in the digital values outputfor the pixels. Decreasing the black level setting will result in anegative offset in the digital values output for the pixels. i.e. Black image emitting photons – adjust black level tocapture or notBlack Level Considerations: Proper use is to ensure camera accurately measures lightwhen scene is darker. Side effect is that it can make the image brighter or darker, butnot by much.
Camera ControlsExample Images of Black Level Effects:Low Black Level used. Good Contrast, but some detailis lost in the darker regions (reduced grey level count)High Black Level used. Contrast suffers, but detail isseen in darker regions (increased grey level count)
Camera ControlsImage Format: The type of image sent from the camera. Usually specified bycolor or mono, and then by bit depth. (i.e. mono8)Image Format Considerations: Higher bit depth more data to transmit/process. Lower bit depth loss of detail Be wary of anyone wishing to “view” a 12 bit image on a computermonitor. All monitors can only display 8 bits or less! Many people think they need 12 bits but don’t!
Camera Controls Example Images of Image Format Effects:8 bit88.2KB/image4 bit44.2 KB/image1 bit11.3KB/image
Camera ControlsColor Format Considerations Color cameras can be as little as 50 more thanmono cameras. But this is not always something you want. Color Images are nice, but usually not found ingeneral machine vision. Color Interpolation does not work well when nocolors are present (i.e. black text on whitebackground). This will affect your image processing! More details later
Camera ControlsResolution (array size): The number of pixels in the sensor,i.e., 640x480Resolution Considerations: More pixels can achieve higher detail. But more pixels is not necessarily better! More pixels small pixels low SNR. Small pixels are hard for lenses to resolve. Always choose the lowest resolution possible for the application. High resolution high price too
Camera ControlsExample Images of Resolution Effects:What if we need to inspect the whole label but also need to read the barcode?
Camera ControlsExample Images of Resolution Effects:HighResolutionLowResolutionThe resolution we choose to read the barcode determines the resolution we needto inspect the whole label.
Summary / Tips Identify whether it is a low or high end application. Low end applications may only need frame rate, resolution, and a sampleimage to select a camera. High end a
The image size in inches relates back to the tube camera. The image format of a tube which could be placed in a 1” deflection coil was called 1” format. The active image size is 16 mm in diagonal. It is the same as for a 16 mm film format. Below is the most common image formats shown. Diagonal: Type 1 . Type 2/3 . Type 1/2 . Type 1/3 .
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2-9V in unit & 2 AA in camera. Match polarities ( ) and ( ). Set camera date back, close camera lens and connect plug to camera port. 2 3 Secure camera, open camera shutter, and slide unit power switch to (ON) and back to (OFF), then push camera test button. Close camera Shutter, remove camera & load film, connect plug to camera, close cover. 4
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