Working of digital camera

Working of Digital CameraWorking of Digital Camera
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Brief History
 In 4th century BC mozi invented camera of Obscura.
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Figure: 1 Camera of Obscura

 1490, Leonardo da Vinci
 1724, Heinrich Schulze and 1822,
Nicephore invented Heliography.
 1833, Louis Daguerre invented
Daguerreotype.
 1839, Robert Cornelius took first
selfie.
 1840, Henry Fox Talbot invented
Calotype.
 1841, Sir John Hershal gives term
photography.
 1957, Russel Kirsch generated
first digital image.
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Figure: 2 Selfie of Robert
Cornelius using Daguerreotype
Contd.

 1975, Steve Sasson invented first
digital camera.
4
Figure: 3 Steven Sasson with first digital camera(left) and first digital image taken
by a digital camera(right)
Source: www.Wikipedia.com
Contd.

Digital camera
• Digital camera is nothing but a box with a hole, you may find some other
parts which helps in better functioning of camera but even today all the
cameras are based on the basic principle of camera of obscura.
• Digital camera sample light from our world, or outer space, spatially,
tonally and by time.
• Digital camera stores image as array of numbers which can only be read
using computer.
• Digital camera work in three phases:
(i) Focus light on sensor in adequate amount.
(ii) Store electrical signal generated by sensor on any storing unit.
(iii) Show the image on digital screen using computer.
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External parts of digital camera
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Figure: 4 External parts of digital camera

Types of Digital Camera
 Compact
 SLR
 Mirrorless interchangeable-lens
cameras
 Digital single-lens reflex camera
(DSLR)
 Digital Single Lens Translucent
(DSLT) cameras
 Line-scan camera
 Infrared camera
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Figure: 5 Compact camera(above)
and DSLR(below)
Source: www.Wikipedia.com

Working of digital camera
• A digital camera takes light and focuses it via the lens onto a sensor made
out of silicon. It is made up of a grid of tiny photosites that are sensitive to
light. Each photosite is usually called a pixel, a contraction of "picture
element"..
• Each photosite on a CCD or CMOS absorbs photons and releases electrons
through the photoelectric effect. The electrons are stored in a well as an
electrical charge that is accumulated over the length of the exposure.
• The charge that is generated is proportional to the number of photons that
hit the sensor.
• This charge is then amplified and sent to A-to-D converter, which gives
DN to voltage on basis of gain factor, this is called stepping.
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Figure: 6 Path of
light when shutter
is closed(top) and
when shutter is
open(bottom)

Digital image
 Spatial sampling: A
digitized image is made up of a
grid of pixels which are
represented by numbers. The
numbers specify the pixel's
location in the grid, and the
brightness of the red, green and
blue colour channels.
 Tonal sampling: Digital
camera measure light and break its
continuously varying tones into
discrete steps.
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Figure: 7 Spatial sampling(top) and tonal sampling(bottom)

 Numbers: Digital image is saved in numbers which makes working easier.
 Linear vs Non linear : Images are stored after non-linear stretching.
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Saving image
Figure: 8 Difference between linear and non-linear stretch.

Sensors
How film works
When shutter is released the film is exposed to light and silver halide crystals
began to breakdown in electron and free silver.
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Figure: 9 Working of silver halide film

Digital Sensor
•A digital sensor is based on photodiode which converts light energy to
electrical energy, a photodiode is a doped semi-conductor mostly silicon
•The P-type and N-type semi-conductor can be combined to make a PN-
junction
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Figure: 10 PN-junction

• Reverse bias type pn-junction is a
photodiode.
• When light of specific wavelength
i.e. 190-1100 nm(which include
visible region) hits a photodiode then
due to absorption of energy of photon
a electron-hole pair is generated.
• Electron run towards n side of
junction which is positively charged
this is called photo-electric effect.
• From here we can measure the
intensity of light by measuring
number of electrons or the voltage.
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Figure: 11 Photo-electric effect
Contd.

CCD & CMOS
• CCD(Charged Coupled Device)
CCD uses no wire instead it uses a single silicon slab divided with insulating
channels, the slab is then coated with thin layer of silicon oxide and tiny strips
of aluminium is laid perpendicular to the channel.
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Figure: 12 Working of CCD

• CMOS(Complementary Metal Oxide Semiconductor)
Like CCD, a CMOS sensor is made out of single piece of silicon. But
instead of shuttling electron row by row, each pixel has a small capacitor
and signal amplifier. This amplified voltage is sent down through tiny
wires into a bus and processed in parallel.
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Figure: 13 Working of CMOS
Contd.

• In CCD the image is recorded
in a single instant, a CMOS
sensor records data line by
line.
• In CMOS the information
collected from the top of the
frame is slightly ahead of
time than the information
from the bottom.
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Figure: 14 Comparison between CMOS and CCD
images
Contd.

Colour Image
• In 1861, Maxwell used RGB i.e. red, green and blue filters separetely to
capture image of a ribbon, on combining these images what he gets was the
first ever color image.
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Figure: 15 Maxwell setup to generate colour image(left) and world’s first
ever colour image(right)

Digital colour
•Digital camera uses additive color
technique to generate color image.
•A CCD detects only light intensity.
•For color photograph we need to
separate the entering light into red,
green and blue, this can be achieved
by following two ways:
(i) Using three sensors.
(ii) Using mosaic filter.
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Figure: 16 Measuring light using three
different filters and CCDs

• In consumer cameras the single
CCD is covered with a filter with
red, green and blue pixel sized
section.
• This creates an as a mosaic of
these three colors.
• The camera applies an algorithm
to estimate correct color for each
pixel.
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Figure: 17 Mosaic filter to take colour photo
using single CCD
Contd.

Reference
Internet Document
1. How Digital Cameras Work
(2015). Available online at http://www.astropix.com/HTML/I_ASTROP/HOW.HTM, updated on 2/2/2015, checked on 10/22/2016.
Abstract:
How Digital Cameras Work
Keywords:
How Digital Cameras Work
Internet Document
Wikipedia (Ed.) (2016):
2. Calotype - Wikipedia.
Available online at https://en.wikipedia.org/w/index.php?oldid=741202483, updated on 10/18/2016, checked on 10/22/2016.
Internet Document
3. Digital camera - Wikipedia.
Internet Document
4. Daguerreotype - Wikipedia.
Internet Document
5. Heliography - Wikipedia.
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Working of digital camera

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