Sounds of Old Technology IB Assessment Statements Topic 14.2., Data Capture and Digital Imaging...
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Transcript of Sounds of Old Technology IB Assessment Statements Topic 14.2., Data Capture and Digital Imaging...
DEVIL PHYSICSTHE BADDEST CLASS ON
CAMPUSIB PHYSICS
TSOKOS LESSON 8-2DIGITAL IMAGINING WITH CHARGE-COUPLED DEVICES
Sounds of Old Technology
IB Assessment Statements
Topic 14.2., Data Capture and Digital Imaging Using Charge-Coupled Devices (CCDs)
14.2.1. Define capacitance.14.2.2. Describe the structure of a
charge-coupled device (CCD).14.2.3. Explain how incident light causes
charge to build up within a pixel.14.2.4. Outline how the image on a CCD
is digitized.
IB Assessment Statements
Topic 14.2., Data Capture and Digital Imaging Using Charge-Coupled Devices (CCDs)
14.2.5. Define quantum efficiency of a pixel.
14.2.6. Define magnification.14.2.7. State that two points on an
object may be just resolved on a CCD if the images of the points are at least two pixels apart.
IB Assessment Statements Topic 14.2., Data Capture and Digital Imaging
Using Charge-Coupled Devices (CCDs)14.2.8. Discuss the effects of quantum
efficiency, magnification and resolution on the quality of the processed image.
14.2.9. Describe a range of practical uses of a CCD, and list some advantages compared with the use of film.
14.2.10. Outline how the image stored in a CCD is retrieved.
14.2.11. Solve problems involving the use of CCDs.
Objectives
Understand the definition of capacitance
Understand the basic operation of a charge-coupled device (CCD)
Define quantum efficiency, magnification, and resolution
Solve problems with CCDs Name the applications of CCDs in
medical imaging
Introductory Video
Capacitors
Any two conductors that are separated by either a vacuum or an insulator
When the switch is closed, does current flow?
What is the end result?
Capacitors
Initially, electrons will flow in a clockwise direction
Negative charge builds up on the bottom plate
Equal positive charge on the top plate What is the difference in charge
called?
Capacitors
The difference in charge is the potential difference or potential (V)
How much of a potential is built up?
Capacitors
The amount of potential is dependent on a property of the material known as capacitance (C)
The amount of charge built up is proportional to the potential difference
CVQ
Capacitors
Capacitance is charge (coulombs) per unit potential (volt) that can build up on a conductor
SI unit for capacitance is the farad (F)
CVQ
VCF 11
Capacitors
Capacitance is based on: Material of conductors Surface area of the plates Distance between the
plates Material between the
plates
CVQ
VCF 11
Charge-Coupled Device
Invented at Bell Labs in 1969 Produces digital images in a fraction of
the time needed for standard photography
Digital images can be easily manipulated, processed and transmitted
Originally designed for use in astronomy Formed the basis for digital cameras,
digital video recorders, digital scanners
Charge-Coupled Device
Consists of a silicon chip covered with light-sensitive elements called pixels
If your camera is 8 megapixels, the camera’s CCD has 8 x 106 pixels on its surface
Each pixel emits electrons when light is incident on it based on the photoelectric effect
Charge-Coupled Device Think of each pixel as a
small capacitor Electrons released by the
photoelectric effect carry a charge, Q
This creates a potential at the ends of the pixel, V, based on the capacitance, C, which can be measured by electrodes attached to the pixel
C
QV
CVQ
Charge-Coupled Device
Energy carried by a single photon of light of frequency f is given by,
where h = 6.63 x 10-34 J-s, Planck’s constant
hfE
Charge-Coupled Device
Since,
where c is the speed of light and λ is the wavelength of light, then
hfE
c
f
hc
E
Charge-Coupled Device
The number of electrons released when light is incident on a pixel is proportional to the intensity of the light incident on the pixel.
Therefore, the charge produced in the pixel (capacitor) and thus the potential difference measured by the electrodes, are proportional to the intensity of light on that pixel
hc
E
Charge-Coupled Device
This will give you the relative brightness of a picture
Think of grayscale
hc
E
Charge-Coupled Device
This is a diagram of a CCD When light is incident on the CCD (shutter
open), charge builds up on each pixel based on the intensity of light incident on each particular pixel
When the shutter closes, a potential difference is applied to each row of pixels
Charge-Coupled Device
The potential difference forces the charge stored in each pixel to move to the row below (hence the name, charge-coupled, charges in one row coupled to charges in the row below)
Charge-Coupled Device
When a row of charges reaches the register, they are moved horizontally, one by one, through an amplifier and then through an analog-to-digital converter
Charge-Coupled Device
The ADC records two pieces of information: Voltage of the pixel Position of the pixel
The process is read until all pixels are read and stored in a file that contains all the information needed to re-create the image
Charge-Coupled Device
The previous discussion showed how to re-create an image based on intensity, but this would only result in a grayscale image
What about color?
Charge-Coupled Device
For color images, pixels are arranged in groups of four, as shown above
There are two with green filters (eyes are most sensitive to green), one with a red filter, and one with a blue filter
Computer algorithms compare the relative intensities for each color to create all the colors of the spectrum
Quantum Efficiency
Not every photon incident on a pixel will result in an electron being released Some will reflect Some will pass straight through
The quantum efficiency of a pixel is the ratio of the number of emitted electrons to the number of incident photons
Quantum Efficiency
Relative quantum efficiencies: Human eye – 1% Photographic Film – 4% CCDs – 70-80%
Note: Not constant at all wavelengths
Because of this, CCDs can measure the brightness of stars (which the HLions will learn all about in Astrophysics)
Magnification
Ratio of the length of an image to the actual length of the object
Magnification of a CCD system is dependent on the properties of the lenses used to focus the light
Resolution
Ability to identify two distinct objects that are close together
On a CCD, two points are resolved if their images are more than two pixel lengths apart
Higher pixel density, higher resolution
Medical Uses of CCDs
Endoscopy – a CCD at the end of a long tube that can be used to create real-time images of internal organs with minimal invasiveness
X-Ray CCDs – use of CCDs in X-ray imagining has cut down the exposure time for patients
HLions will learn more about X-Ray imaging in Medical Physics!
Summary Video – How CCDs are Made
Objectives
Do you understand the definition of capacitance?
Do you understand the basic operation of a charge-coupled device (CCD)?
Can you define quantum efficiency, magnification, and resolution?
Can you solve problems with CCDs? Can you name the applications of
CCDs in medical imaging?
IB Assessment Statements
Topic 14.2., Data Capture and Digital Imaging Using Charge-Coupled Devices (CCDs)
14.2.1. Define capacitance.14.2.2. Describe the structure of a
charge-coupled device (CCD).14.2.3. Explain how incident light causes
charge to build up within a pixel.14.2.4. Outline how the image on a CCD
is digitized.
IB Assessment Statements
Topic 14.2., Data Capture and Digital Imaging Using Charge-Coupled Devices (CCDs)
14.2.5. Define quantum efficiency of a pixel.
14.2.6. Define magnification.14.2.7. State that two points on an
object may be just resolved on a CCD if the images of the points are at least two pixels apart.
IB Assessment Statements Topic 14.2., Data Capture and Digital Imaging
Using Charge-Coupled Devices (CCDs)14.2.8. Discuss the effects of quantum
efficiency, magnification and resolution on the quality of the processed image.
14.2.9. Describe a range of practical uses of a CCD, and list some advantages compared with the use of film.
14.2.10. Outline how the image stored in a CCD is retrieved.
14.2.11. Solve problems involving the use of CCDs.
QUESTIONS?
#1-25
Homework