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Image Sensing& Aquisition
Presentation by Shashank Ram
12SS1A0446Dept. of ECE, JNTUH-
CES
ContentsWhich we will be covering
Digital Photo Sensing
Camera and it’s classification
Camera components and History
Analog photo sensing
Conclusion
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Camera ClassificationBased on the photo sensing element
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Sensor Sizes :Various image sensor sizes
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Camera ObscuraDark Room in
Latin. A pin-hole camera
Silver NitrideReacts on
exposure to light
History of CameraA Timeline of the Camera Saga…..
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Daguerreotype CameraA lens is used instead on a pin-hole camera
FilmIt reacts differently with different exposures of light.More durable.Roll film Camera
Compact and can accommodate more film .
Color film and DarkroomColor film is developed .
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Advent of SLRProfessional cameras with optical viewfinders are introduced.SLR: Single Lens Reflex
Auto Focus RevolutionWith the addition of auto-focus many novice joined the SLR wagonDSLR
With the advent of transistors and digital logic this should be expected
CMOSCMOS sensors made the DSLRs more economical
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Compact & MirrorlessWith the help of cmos small pocket cameras and cameras with no mirror for OVF developed using EVF
Machine Vision & VRComputer vison,AR & VR are the future applications
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Lens
Aperture
PhotoSensi
ng eleme
nt
Shutter
Buffer
ISP
Storage
Photon to BitImage Acquisition step by step
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Microlenses
Microlens layer
Color filter layer
Metal opaque layer Photodetector Silicon substrate
•Main camera lens brings image to microlenses.
•Microlens funnels photons to active detector area.
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Bayer FilterA Color filter Array
(assumes UV and NIR filters)
• Each pixel gets covered by a colored filter– We use red, green, blue (RGB) CFA - best match for RGB
displays– Pixel colors arranged in “Bayer” pattern G R B G
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Photons to ElectronsThe essence of sensing an image
SiSi
Si Si
Si
Eh
e-e+
Covalently bonded silicon e-e+
P+
N
P
P+
h
Pinned photodiode
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• MOS-based charge-coupled devices (CCDs) shift charge one step at a time to a common output amplifier
CCD Image SensorYour great subtitle in this line
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Camera on a ChipActive pixel arrayAnalog signal chainAnalog-to-Digital Conv.VLSI Digital logic
I/O interface Timing and control Exposure control Color processing
CMOS SensorThe new age king!!
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CircuitryCMOS Sensor Circuitry
Read pixel signals out thru switches and wires
Timing And
Control Logic
Photodetector converts photons to electrons
Amplifier converts electrons to voltage after intrapixel complete charge transfer
Analog signal processor suppresses noise and further amplifies signal
Column multiplexer selects particular column(s) for routing to ADC(s)
Analog-to-digital converters (ADC) converts signal from volts to bits (usually 10 bits
Row select logic chooses which row is selected for readout.
Timing and control logic controls the timing of the whole sensor
Analog Signal Proc Column MuxADC ADC
resolution)
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Camera System-on-a-Chip integration is extensive•Color interpolation•Color correction, white balance•Dark signal correction, gamma and other normal corrections•Lens shading corrections•Format conversion and compression•Exposure control•Flicker detection and avoidance•Defect identification and correction•Auto focus support (focus score, actuator control)•Etc.
On-Chip ISPISP: Image Signal Processor
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Color InterpolationInterpolate = to estimate
Goal is to get best approximation for RGB at each pixel site but we start with just red, green or blue, not all 3.
Many ways to do color interpolation, for example:•Have blue, need green & red
• G = average of 4 neighboring greens• R = average of 4 neighboring reds
•Have green, need blue & red• B = average of 2 neighboring blues• R = average of 2 neighboring reds
•Have red, need green & blue• G = average of 4 neighboring greens• B = average of 4 neighboring blues
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Light OutEverything that glitters isn't GOLD
Image on screen should look like image seen, but better
Human eye response to color
LED LCD display color Spectrum and tuning
Computer processing
Silicon response andOn-chip processing
Camera processing
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• CMOS image sensors can incorporate other circuits on the same chip, eliminating the many separate chips required for a CCD.
• Not only does this make the camera smaller, lighter, and cheaper; it also requires less power so batteries last longer.
• Image stabilization and Image compression can be done on chip.• CMOS suffer in low light conditions due to less fill factor.
• The percentage of a pixel devoted to collecting light is called the pixel’s fill factor
• Less fill factor because each photosite is covered with circuitry that filters out noise and performs other functions.
• CMOS has more complex pixel and chip whereas CCD has a simple pixel and chip
• CCDs don’t suffer from rolling shutter effect as in CMOS• Hence CCDs are preferred in video.
But with BSI(back side illumination) and good image processing algorithms CMOS is winning the camera sensor battle!
CCD vs CMOSThe Battle begins….
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Resolution:The resolution of digital sensors is calculated by individual pixels , where as in film the resolution is estimated.
Resoltion of a large/medium format film is definitely very high (when scanned) compared to digital.
Noise/Grain:Digital sensors are more prone to noise where as film has the aesthetically pleasing grain.
Dynamic Range:Both compete head to head in this area.Film does well with highlights,where as digital with midtones..
Compactness and Ease of Development:In this regard Digital easily wins over Analog with more compactness and many post processing tools available at disposal.
Physical Darkroom vs Adobe Lightroom.
Analog(film) vs DigitalThe age old Debate….
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Image sensors have come along way since the 1st generation device – the CCD.
The 2nd generation device, the CMOS active pixel image sensor is going strong. “Billions and billions served”
• Image sensors are an emergent solution for practically every automation-focused machine-vision application.
• New electronic fabrication processes, software implementations, and new application fields will dictate the growth of image-sensor technology in the future.
ConclusionConcluding remarks……..
THANK YOUFor listening patiently