Photo Forensics Flashcards
How does sensitivity to infrared light get reduced?
By a filter
What is the role of the lens?
Focuses the light onto the sensor
What do these mean?
Y
Y’
S
S’
F
Y = height of object
Y’ = height of image
S = distance of object from the lens
S’ = distance of the focused image from the lens
F = focal length
Equation for: object image relation
1/f = 1/s + 1/s’
Equation for magnification (m) = y’/y
M = - s’/s
Infrared filter
The eye is not sensitive to infrared lights, however a camera sensor is sensitive to infrared light.
What are the two common configurations of colour filter array?
Stripe and Bayer
In colour filter array, what colour light does the red filter allow through?
Red light
What are the two main types of sensors?
- CCD (Charged couple devices)
- CMOS (complementary metal oxide semiconductor)
What do CCD and CMOS consist of?
They both have tightly packed light sensitive photodiodes, constructed on a silicon wafer.
What are photodiodes?
- Semi-conductor devices
- that generate an electrical charge
- in proportion to the number of photons that reach them
Advantages and Disadvantages of CCD sensors…
Advantages:
- proven record of technologies and commercialisation
- low noise
- High S/N
Disadvantages:
- high power consumption
- slow speed
- on-chip peripheral circuits, difficult to manufacture
Advantages and disadvantages of CMOS sensors?
Advantages:
- manufacture can be simpler and less expensive
- uses less power than CCD
Disadvantages:
- relatively high noise
How many values per pixel do colour images have?
3 values per pixel
How many values per pixel do monochrome (grey images) have?
1 value per pixel
