Digital Forensics

Question 1

What is the job of the lens?

Answer 1

To focus light/image onto centre

Question 2

What is the job of the filter?

Answer 2

Reduce the sensitivity to infrared light

Question 3

What is the job of the sensor?

Answer 3

Turns light into a recordable image

Question 4

What does the DSP unit do?

Answer 4

Performs some basic image processing before the image is saved

Question 5

What is the focal point?

Answer 5

A point on the optic axis where parallel light rays converge

Question 6

What is the optic axis?

Answer 6

A line which runs perpendicular to the lens and directly through the middle

Question 7

What does CMOS stand for? And what is its use?

Answer 7

Complementary metal oxide semiconductor
It helps the light sensitive sensor chip to record all of the data in a very short space of time

Question 8

What does DSLR stand for?

Answer 8

Digital single lens reflex

Question 9

What are pixels?

Answer 9

Individual light sensitive cells which measure the amount of light that fall on them. They cover the cameras sensor

Question 10

How are coloured images produced?

Answer 10

The light seen by the camera is split in to the three primary colours which can than be used to create an accurate image through the use of a Bayer filter

Question 11

What is a Bayer filter?

Answer 11

A grid of coloured filters that sit over the sensor with red, green, and blue elements over individual pixels which will only allow their respective light colours through. It looks at pixels surrounding others to formulate an informed guess of what the true colour of that pixel is

Question 12

What is the job of the colour filter array?

Answer 12

It allows the digital camera to ‘see’ colours as it is colourblind without this and can only determine light intensity

Question 13

What are the two common configurations of the colour filter array? Can you describe them?

Answer 13

The Bayer pattern - checkered
The Stripe pattern - stripes

Question 14

What are photo sites?

Answer 14

Each square on the sensor element is a single photo site

Question 15

Why are there two times more green elements on the colour filter array compared to red and blue?

Answer 15

Due to the human eye being more sensitive to green light

Question 16

What are the two main types of sensors in the camera?

Answer 16

CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor)

Question 17

Define photodiodes

Answer 17

Semiconductor devices that generate an electrical charge in proportion to the number of photons which reach them

Question 18

Where are photodiodes typically found?

Answer 18

They are tightly packed on a silicone wafer in CCDs and CMOSs

Question 19

What are the advantages of CCD sensors?

Answer 19

• Proven record of technologies and commercialization
• Low noise, high S/N because the surface is almost entirely photosensitive (compared to 1/4 in CMOS)

Question 20

What are the disadvantages of CCD sensors?

Answer 20

• High power consumption, slower speed
• on-chip peripheral circuits difficult to manufacture

Question 21

What are the advantages of CMOS sensors?

Answer 21

• Manufacture can be simpler and less expensive
• Use less power than CCD
• Physical size of detector is smaller

Question 22

What are the disadvantages of CMOS sensors?

Answer 22

• Relatively high noise

Question 23

Where are CMOS sensors and CCD sensors typically used?

Answer 23

CMOS - modern consumer cameras (phones)
CCD - scientific applications

Question 24

What is the job of the DSP (digital signal processors) molecule?

Answer 24

To read out the voltages from the image sensor which are then fed into an onboard image processing module which contains proprietary algorithms for improving the perceived quality, demosaicing, and compression

Question 25

Define spacial sampling

Answer 25

The average light intensity per pixel

Question 26

How many values per pixel to monochrome images have?

Answer 26

One

Question 27

Why does the image appear blurry when the light intensity pattern is continuous?

Answer 27

Each pixel only record the average light intensity

Question 28

Define resolution

Answer 28

The dimensions by which you can measure how many pixels are on a screen

Question 29

Why are sharper images shown on a phone compared to a laptop?

Answer 29

They both have the same number of pixels, but they are in a denser space on the phone

Question 30

What is a byte?

Answer 30

8 bits

Question 31

How do we make an image darker?

Answer 31

By subtracting a fixed constant from each of the RGB values