DIGITAL PHOTOGRAPHIC DIGITAL PHOTOGRAPHIC IMAGING IMAGING

Lecture 2 – How does a Lecture 2 – How does a Digital Camera Digital Camera

Work ?Work ?

Early DaysEarly Days

NeedNeed for other for other forms imagingforms imaging

Atomic ageAtomic age

No silver based No silver based filmfilm

The First Digital CameraThe First Digital Camera

Steven Sasson invented the first digital Steven Sasson invented the first digital camera in 1975. camera in 1975.

It weighed 8 pounds (3.6 kg) and had It weighed 8 pounds (3.6 kg) and had only 0.01 megapixels. only 0.01 megapixels.

The image was recorded onto a The image was recorded onto a cassette tape and this process took 23 cassette tape and this process took 23 seconds. seconds.

His camera took images in black and His camera took images in black and white white

History of Digital CamerasHistory of Digital Camerasmid-1970s, Kodak invented solid-state image mid-1970s, Kodak invented solid-state image sensors that "converted light to digital pictures" sensors that "converted light to digital pictures" for professional and home consumer use.for professional and home consumer use.

In 1986, Kodak scientists invented the world's In 1986, Kodak scientists invented the world's first megapixel sensor, capable of recording 1.4 first megapixel sensor, capable of recording 1.4 million pixelsmillion pixels

In 1991, Kodak released the first professional In 1991, Kodak released the first professional digital camera system (DCS), aimed at digital camera system (DCS), aimed at photojournalistsphotojournalists. It was a Nikon F-3 camera . It was a Nikon F-3 camera equipped by Kodak with a 1.3 megapixel equipped by Kodak with a 1.3 megapixel sensor. sensor.

The first digital cameras for the consumer-level The first digital cameras for the consumer-level market that worked with a home computer via a market that worked with a home computer via a serial cable were the Apple QuickTake 100 serial cable were the Apple QuickTake 100 camera (February 17 , 1994), the Kodak DC40 camera (February 17 , 1994), the Kodak DC40 camera (March 28, 1995), the Casio QV-11 camera (March 28, 1995), the Casio QV-11 (with LCD monitor, late 1995), and Sony's (with LCD monitor, late 1995), and Sony's Cyber-Shot Digital Still Camera (1996). Cyber-Shot Digital Still Camera (1996).

Canon EOS 300D (2003)Canon EOS 300D (2003)

The first digital SLR (single lens reflex) camera that cost The first digital SLR (single lens reflex) camera that cost less than 1000 euros (£830). less than 1000 euros (£830).

At the time amateurs, and many professionals too, could At the time amateurs, and many professionals too, could only afford digital compact cameras or what were called only afford digital compact cameras or what were called "bridge cameras" - models with long range zooms that "bridge cameras" - models with long range zooms that couldn't come off the body. couldn't come off the body.

This marked the beginning of the This marked the beginning of the fall in the price fall in the price of of proper digital cameras.proper digital cameras.

““The new approach [Digital Photography] has The new approach [Digital Photography] has been enormously successful”. been enormously successful”.

““Since film still provides better picture quality, Since film still provides better picture quality, digital cameras have not completely replaced digital cameras have not completely replaced conventional camerasconventional cameras”. ”.

““But, as digital imaging technology has But, as digital imaging technology has improved, digital cameras have rapidly improved, digital cameras have rapidly become more popular”. become more popular”.

More Arguments…..More Arguments…..

Conventional digital cameras Conventional digital cameras strugglestruggle to deliver beautiful to deliver beautiful images in high-contrast scenes, because it is extremely images in high-contrast scenes, because it is extremely difficult in such settings to avoid both difficult in such settings to avoid both washed-out washed-out highlightshighlights and and pitch-black shadows pitch-black shadows with a single with a single exposure adjustment. exposure adjustment.

Compounding the problem is the fact that white-washed Compounding the problem is the fact that white-washed highlights are impossible to save — even with the highlights are impossible to save — even with the assistance of advanced image editing or retouching assistance of advanced image editing or retouching applications — applications — because they carry no image data to because they carry no image data to begin withbegin with. .

The Digital Compact CameraThe Digital Compact Camera

1.1. Battery Battery compartment:compartment:

2.2. Flash Flash capacitor:capacitor:

3.3. Flash lamp:Flash lamp:

4.4. LED:LED:

5.5. Lens:Lens:

6.6. Focusing Focusing mechanism:mechanism:

7.7. CCDCCD::

The Digital SLR CameraThe Digital SLR Camera

Why are digital cameras Why are digital cameras replacing film cameras?replacing film cameras?

1.1. You can You can see your pictures see your pictures within seconds of taking within seconds of taking them. them.

2.2. If you don’t like the picture you’ve taken, If you don’t like the picture you’ve taken, you can delete you can delete it it – no more paying for pictures that didn’t turn out. – no more paying for pictures that didn’t turn out.

3.3. Computer software programs allow you to do a variety of Computer software programs allow you to do a variety of things with your photos, like file them in albums on the things with your photos, like file them in albums on the Internet, email them, Internet, email them, manipulatemanipulate them (crop out the ex- them (crop out the ex-partner, or take out the red-eye), adjust the brightness, partner, or take out the red-eye), adjust the brightness, contrast or colour, and much more. contrast or colour, and much more.

4.4. ? Cheaper – no silver? Cheaper – no silver

5.5. Some Digital cameras are Some Digital cameras are smaller and lightersmaller and lighter, easier to , easier to handle. handle.

6.6. The initial cost pays for everything at once, The initial cost pays for everything at once, no more no more buying film buying film and and paying for developing paying for developing for every roll. for every roll.

7.7. The CCD (the electronic part of the digital camera that The CCD (the electronic part of the digital camera that converts your image into digital format) captures converts your image into digital format) captures 70% 70% of of the available light, while photographic film captures only the available light, while photographic film captures only 2%. 2%.

To add to you To add to you Blog/Sketchbook ?Blog/Sketchbook ?

What advantages do you feelWhat advantages do you feel

Digital has over Film ?Digital has over Film ?

FilmFilm

How do digital cameras work – in How do digital cameras work – in a nut shell? a nut shell?

based on similar photographic processes as based on similar photographic processes as those used in those used in film photographyfilm photography

the biggest difference between them and their the biggest difference between them and their predecessors (film) is the replacement of film predecessors (film) is the replacement of film with with light-sensitive sensorslight-sensitive sensors

Here, the Here, the light sensor light sensor device absorbs the device absorbs the light light particles particles and converts them into and converts them into electrical electrical chargescharges

Sensors can be thought of as a grid of thousands Sensors can be thought of as a grid of thousands or millions of solar cells which transform the or millions of solar cells which transform the image into an electrical charge.image into an electrical charge.

The The biggerbigger the hit of light to the sensors, the the hit of light to the sensors, the greatergreater the electrical charge produced, which the electrical charge produced, which means the photo will be more exposed. means the photo will be more exposed.

next step is to next step is to readread the accumulated charge of the accumulated charge of eacheach

When capturing and converting these charges, When capturing and converting these charges, the sensor cells are the sensor cells are colour-blindcolour-blind, recognising , recognising only the only the intensityintensity of the light. of the light.

Digital cameras, therefore, have to employ Digital cameras, therefore, have to employ coloured filters to produce the spectrum of coloured filters to produce the spectrum of colours which is present in the picture.colours which is present in the picture.

the final step is to convert the the final step is to convert the analogueanalogue signal to a signal to a digitaldigital one by passing the one by passing the information on the sensor through an information on the sensor through an analogue to digital converter. analogue to digital converter.

This will turn the information into binary This will turn the information into binary form, which can then be interpreted by a form, which can then be interpreted by a PC.PC.

The predominant sensor used is a The predominant sensor used is a Charge Charge Coupled Device Coupled Device (CCD), (CCD), although although Complementary Metal Oxide Semiconductor Complementary Metal Oxide Semiconductor (CMOS) (CMOS) sensors are increasingly popular.sensors are increasingly popular.

Generally a Generally a larger sensor larger sensor will produce a will produce a better better quality imagequality image, as it is able to capture more light, , as it is able to capture more light, which is one of the chief reasons why DSLRs which is one of the chief reasons why DSLRs offer superior image quality to smaller compact offer superior image quality to smaller compact cameras.cameras.

But the size of the sensor is less important than the But the size of the sensor is less important than the number of pixels it has. number of pixels it has. OR DOES IT OR DOES IT – – Mega Pixel Myth Mega Pixel Myth

Spatial ResolutionSpatial Resolution: the ability of any image-forming : the ability of any image-forming device such as a camera, to distinguish small details of device such as a camera, to distinguish small details of an object, thereby making it a major determinant of an object, thereby making it a major determinant of image resolutionimage resolution

Which photo has the more pixels ?Which photo has the more pixels ?

Film - Camera Lens & DigitalFilm - Camera Lens & Digital

Note - most Note - most sensorssensors in digital cameras are in digital cameras are smallersmaller than their film counterpart, so the than their film counterpart, so the lens required to produce similar-sized lens required to produce similar-sized images via a digital camera is smaller or images via a digital camera is smaller or Focal length is different.Focal length is different.

Sensor Sizes

Typical sensor size of 3, 4, and 5 megapixel digital compact cameras

Typical sensor size of 6 megapixel digital SLRs

Digital vs Film PhotographyDigital vs Film Photography

35mm film can potentially contain at least 35mm film can potentially contain at least 10 – 20 megapixels10 – 20 megapixels

equivalent to say a 3900x2600 pixel image equivalent to say a 3900x2600 pixel image filefile

Digital cameras today : 10 megapixels +Digital cameras today : 10 megapixels +

HD Films

Future or Gimmick ?Future or Gimmick ?

““We already have quality you can print wall We already have quality you can print wall sized, we don't actually *need* more pixels in the sized, we don't actually *need* more pixels in the image, what we need is more accuracy and image, what we need is more accuracy and realism in the detail they pick uprealism in the detail they pick up”.”.

Today's 20+MP cameras are already Today's 20+MP cameras are already stretching stretching lenses.lenses.

Canon's 120-megapixel CMOS sensor

LensLens

Mega Pixels

What is a Sensor?What is a Sensor?

We now know Digital cameras capture their We now know Digital cameras capture their images on a silicon semiconductor referred to as images on a silicon semiconductor referred to as a digital sensor. a digital sensor.

composed of an array of photosensitive diodes composed of an array of photosensitive diodes called called photositesphotosites that capture photons that capture photons (subatomic light particles) and converts them to (subatomic light particles) and converts them to electrons. electrons.

This build up of electrons in each photosite is This build up of electrons in each photosite is converted to a converted to a voltagevoltage which in turn is converted which in turn is converted to digital data as a picture element or ‘to digital data as a picture element or ‘pixelpixel’. ’.

Light = WaterLight = Water

Photosite = BUCKETPhotosite = BUCKET

WaterWater rather than rather than lightlight - poured - poured

NoNo water – water – NoNo electrical charge electrical charge therefore – image is therefore – image is BLACKBLACK

LotsLots of water – bucket of water – bucket fullfull therefore image is WHITEtherefore image is WHITE

sensorssensors

PhotositePhotosite

Photosite collectsLight photons

Readout from the photosite

LensLight

But the ‘image’ is But the ‘image’ is black and whiteblack and white

monochromemonochrome

Capturing ColourCapturing Colour

Sensors (photosite) Sensors (photosite) can not see can not see colour. colour.

In order to get a full colour image, most In order to get a full colour image, most sensors use sensors use filteringfiltering to look at the light in its to look at the light in its threethree primaryprimary colourscolours. .

Once the camera records all three colours, it Once the camera records all three colours, it combines them to create the full spectrum. combines them to create the full spectrum.

Types of Digital SensorsTypes of Digital Sensors

In the digital camera world there In the digital camera world there are basically two types of digital are basically two types of digital sensors: sensors:

CCDCCD and and CMOSCMOS, with some new , with some new and exciting technologies on the and exciting technologies on the horizon.horizon.

CCD SensorsCCD Sensors

Charged Coupling Device Charged Coupling Device (CCD) sensors were invented (CCD) sensors were invented by Dr. Willard Boyle and Dr. George Smith at Bell Labs in by Dr. Willard Boyle and Dr. George Smith at Bell Labs in 1969.1969.

CCD sensors - name from how the charge is read after CCD sensors - name from how the charge is read after an image is captured. an image is captured.

the sensor is able to transport the built up charge across the sensor is able to transport the built up charge across itself without compromising the image quality. itself without compromising the image quality.

The first row of the array is read into an output register, The first row of the array is read into an output register, which in turn is fed into an amplifier and an analogue to which in turn is fed into an amplifier and an analogue to digital converter. digital converter.

After the first row has been read, it is dumped from the After the first row has been read, it is dumped from the read out register and the next row of the array is read into read out register and the next row of the array is read into the register. the register.

The charges of each row are ‘coupled’ so as each row The charges of each row are ‘coupled’ so as each row moves down and out, the successive rows follow in turn. moves down and out, the successive rows follow in turn.

The digital data is then stored as a file that can be viewed The digital data is then stored as a file that can be viewed and manipulated.and manipulated.

““Until recently, CCD sensors have been predominant in Until recently, CCD sensors have been predominant in digital cameras because of their digital cameras because of their high quality/ low noise high quality/ low noise images and their maturity, having been produced for over images and their maturity, having been produced for over thirty years”. thirty years”.

““new manufacturing methods of an old technology have new manufacturing methods of an old technology have led to inroads for it to surpass CCD sensors”.led to inroads for it to surpass CCD sensors”.

CMOS sensorsCMOS sensors

CMOS (CMOS (Complimentary Metal Oxide SemiconductorComplimentary Metal Oxide Semiconductor) ) sensors or Active Pixel sensors - first discussed in a sensors or Active Pixel sensors - first discussed in a paper from Dr. Eric Fossum, a scientist at NASA’s Jet paper from Dr. Eric Fossum, a scientist at NASA’s Jet Propulsion Laboratory, in 1992. Propulsion Laboratory, in 1992.

1993 through to 1995, JPL developed much of the 1993 through to 1995, JPL developed much of the technology which would be implemented into the CMOS technology which would be implemented into the CMOS sensor. sensor.

In 2001, Micron Technology used its extensive In 2001, Micron Technology used its extensive knowledge of CMOS knowledge of CMOS waferwafer manufacturing to enhance the manufacturing to enhance the development further.development further.

CMOSCMOS sensors derive their name from the way they are sensors derive their name from the way they are manufactured. manufactured.

They are cut from a CMOS wafer which is cheaper to They are cut from a CMOS wafer which is cheaper to produce then a CCD wafer, provides produce then a CCD wafer, provides less power less power consumptionconsumption, and also allow for more involved circuitry , and also allow for more involved circuitry along side of the photosite array. along side of the photosite array.

Each photosite in the CMOS sensor has Each photosite in the CMOS sensor has three or more three or more transistorstransistors which has its benefits and its draw backs. which has its benefits and its draw backs.

The transistors allow for processing to be done right at The transistors allow for processing to be done right at the photosite, and each pixel/photosite can be accessed the photosite, and each pixel/photosite can be accessed independently. independently.

Because the transistors occupy space on the array, some Because the transistors occupy space on the array, some of the of the incoming light hits the transistors incoming light hits the transistors and not the and not the photosites, which leads to picture noise. photosites, which leads to picture noise.

CMOSCMOS sensors also function at a very low gain which sensors also function at a very low gain which may contribute to noise.may contribute to noise.

CCD vs. CMOS Sensors

CCD CMOS

cost

expensive to produce because of special manufacturing methods employed

inexpensive because CMOS wafers are used for many different types of semiconductors

powerconsumes upto 100x more power than CMOS

low power consumption

noisehigh quality, low noise images

susceptible to noise

maturityproduced for longer period; higher quality images, more pixels

less mature but equal in low and middle range resolutions to CCD

extended functionalitytechnically feasible; other chips are used

other circuitry easily incorporated on same chip

fill factor high low

CCD vs. CMOS Sensors

For Your Blog/SketchbookFor Your Blog/Sketchbook

What type of sensor do you What type of sensor do you have in your camera ?have in your camera ?

Answer for class next time Answer for class next time pleaseplease

Next time – how we get Next time – how we get colour !colour !