Sensor Flashcards
(rough) order/summary of events from camera capturing - to saving to media
- Light to Charge Conversion – light hits sensor, converted to charge
- Charge Accumulation – once all photosites are filled
- Charges Transfer –for a CCD Chip charges are transferredvia shift register
- Charge to Voltage Conversion – for a CCD Chip charges are converted one by one to voltage
- Amplification (Analog/Digital) Conversion – Voltage is Amplified to a larger signal
- A/D Conversion – Voltage is converted to digital signal
What is The CCD Sensor, and a brief background
Charged Coupled Device. invented in 1969 by scientists at Bell Labs in New Jersey, USA. For years, it was the prevalent technology for capturing images, from digital astrophotography to machine vision inspection. The CCD sensor is itself an analog device, but the output is immediately converted to a digital signal by means of an analog-to-digital converter (ADC)
How does voltage conversion work differently on CCD Sensor than CMOS
During Readout CCD’s Move Electrons from pixel to pixel like a bucket brigade via horizontal shift registers and vertical shift registers. And One by one each charge is converted in The Voltage Converter.
Pros of CCD Sensor (5)
- Single Charge transfer process is slow but also leads to the high sensitivity and pixel-to-pixel consistency of the CCD. -
- Global Shutter
- Superior Noise/Sensitivity (low light application)
- Dynamic Range
- Utilizes an image processor that is separate from the sensor
CONS of CCD Sensor (2)
- You can’t get the data off the [CCD sensor] quickly enough, because there is a limit to the number of readout channels. (no live feed)
- Blooming (distortion) –( because CCD sensors allow easy vertical shifting. When sensor is exposed for a long time. Pixel site can over saturate vertically adjacent pixels)
What is the CMOS and a brief background
The Complementary Metal Oxide Semiconductor (CMOS) was invented in 1963 by Frank Wanlass. However, he did not receive a patent for it until 1967, and it did not become widely used for imaging applications until the 1990s. CMOS is a digital device. Known as the active pixel sensor, bundles image sensor and processor into a single chip
How does CMOS Voltage and A/D Conversion Work
The charge to voltage conversion and voltage amplification is carried out in the pixel itself Each site is essentially a photodiode and three transistors, performing the functions of resetting or activating the pixel, amplification and charge conversion, and selection or multiplexing The voltage is read line by line, vertically, from up to down.
Benefits of the CMOS (6)
- requires less power than CCD Sensors. -tend to be smaller (b/c less circuitry required)
- has much faster processing speed than CCD Sensors. -peripheral circuit is built into it (allowing for it to do it’s own conversion)
- traditionally CCD’s have better better sensitivity, but nowadays using different techniques like microlens on each pixel of CMOS sensor, the sensitivity can be increased.
- handles high light levels without blooming
- cheaper to manufacture
CONS of the CMOS (3)
- Rolling Shutter: (The voltage is read line by line, vertically, from up to down. Makes it susceptible to distortion during recorded movement.) -
- less sensitivity (low light application) -
- less available space for light capture, (because each site does its own voltage conversion)
What is a 3CCCD
A three-CCD (3CCD) camera is a camera whose imaging system uses three separate charge-coupled devices (CCDs), each one receiving filtered red, green, or blue color ranges
Where in the process of video recording does GAIN occur
Increases amplification of signal before A/D conversion.
Downside of increasing Gain
this amplifies the whole signal, including any associated background noise.
What is AutoGain (abbreviated as AGC)
Most cameras have automatic gain, or autogain Some allow the user to turn it off or set it manually. It is important to note that gain after the ADC is not true gain, but rather digital gain. Digital gain uses a look up table to map the digital values to other values, losing some information in the process.
When is Gain useful
Gain before the ADC can be useful for taking full advantage of the bit-depth of the camera in low light conditions,
What is Gamma
Gamma is a digital camera setting that controls the grayscale reproduced on the image.Gamma can be thought of as the ability to stretch one side (either black or white) of the dynamic range of the pixel. This control is often used in signal processing to raise the signal-to-noise ratio (SNR).
