digital cameras 061401 siddharth chauhan

8/9/2019 Digital Cameras 061401 Siddharth Chauhan

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DIGITALCAMERAS


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Introduction In the past twenty years, most of the major

technological breakthroughs in consumerelectronics have really been part of onelarger breakthrough:-

converting conventional analoginformation (represented by a fluctuating

wave) into digital information(represented by ones and zeros, or bits).This fundamental shift in technologytotally changed how we handle visualand audio information -- it completelyredefined what is possible.

The digital camera is one of the mostremarkable instances of this shift


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Introduction Essentially, a digital image is just a long string

of 1s and 0s that represent all the tiny coloreddots -- or pixels -- that collectively make up theimage.

This can be done by sampling the original lightthat bounces off the subject, immediately

breaking that light pattern down into a series ofpixel values.

Just like a conventional camera, it has a series oflenses that focus light to create an image of ascene. But instead of focusing this light onto apiece of film, it focuses it onto

a semiconductor device that records lightelectronically. A computer then breaks thiselectronic information down into digital data.


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CCD and CMOS: FilmlessCameras

Instead of film, a digital camera has a sensorthat converts light into electrical charges.

The image sensor employed by most digitalcameras is a charge coupled device (CCD).Some cameras use complementary metal oxidesemiconductor (CMOS) technology instead.

Both CCD and CMOS image sensors convert

light into electrons. A simplified way to think about these sensors is

to think of a 2-D array of thousands or millionsof tiny solar cells.

Once the sensor converts the light intoelectrons, it reads the value (accumulatedcharge) of each cell in the image. This is wherethe differences between the two main sensortypes kick in:

CCD


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CCD and CMOS: FilmlessCameras

A CCD transports the charge across thechip and reads it at one corner of thearray. An analog-to-digital converter(ADC) then turns each pixel's value into adigital value by measuring the amount ofcharge at each photosite and converting

that measurement to binary form. CMOS devices use several transistors at

each pixel to amplify and move thecharge using more traditional wires.

CMOS

Sensor


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CCD


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CMOS SENSOR


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Pros And Cons of The Two

Sensors CCD sensors create high-quality, low-noise images. CMOS sensors are

generally more susceptible to noise.

Because each pixel on a CMOS sensor has several transistors locatednext to it, the light sensitivity of a CMOS chip is lower. Many of the

photons hit the transistors instead of the photodiode. CMOS sensors traditionally consume little power. CCDs, on the other

hand, use a process that consumes lots of power. CCDs consume asmuch as 100 times more power than an equivalent CMOS sensor.

CCD sensors have been mass produced for a longer period of time, sothey are more mature. They tend to have higher quality pixels, andmore of them.

Although numerous differences exist between thetwo sensors, they both play the same role in the

camera -- they turn light into electricity.


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CCD vs. CMOS Sensors

CCD CMOS

cost expensive to producebecause of specialmanufacturing methodsemployed

inexpensive because CMOSwafers are used for manydifferent types ofsemiconductors

power consumes upto 100x more

power than CMOS

low power consumption

noise high quality, low noise images susceptible to noise

maturity produced for longer period;higher quality images,

more pixels

less mature but equal in lowand middle range

resolutions to CCD

Extendedfunctionality

technically feasible; otherchips are used

other circuitry easilyincorporated on samechip


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Digital Camera Resolution The amount of detail that the camera can capture is

called the resolution, and it is measured in pixels. Themore pixels a camera has, the more detail it can captureand the larger pictures can be without becoming blurry or"grainy."

Some typical resolutions include: 256x256 - This is 65,000 total pixels. 640x480 - This resolution is ideal for e-mailing pictures or

posting pictures on a Web site. 1216x912 - This is a "megapixel" image size -- 1,109,000 total

pixels 1600x1200 - With almost 2 million total pixels. You can print a

4x5 inch. 2240x1680 - Found on 4 megapixel cameras. Prints up to 16x20

inches. 4064x2704 - A top-of-the-line digital camera with 11.1

megapixels. You can create 13.5x9 inch prints with no loss ofpicture quality.


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Capturing Color Unfortunately, each photosite is colorblind. It only keeps

track of the total intensity of the light that strikes itssurface. In order to get a full color image, most sensorsuse filtering to look at the light in its three primary colors

Once the camera records all three colors, it combinesthem to create the full spectrum.


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Capturing Color

The highest quality cameras use three separate sensors,each with a different filter. A beam splitter directs lightto the different sensors.

Each sensor gets an identical look at the image; but

because of the filters, each sensor only responds to oneof the primary colors


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Capturing Color

Another method is to rotate aseries of red, blue and greenfilters in front of a single sensor.The sensor records three

separate images in rapidsuccession. This method alsoprovides information on allthree colors at each pixellocation; but since the threeimages aren't taken at preciselythe same moment, both the

camera and the target of thephoto must remain stationaryfor all three readings.


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Capturing Color

So basically a camera captures each image on

a separate CCD array.


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PIXEL

A pixel is a contraction if the term PIcture ELement.Digital images are made up of small squares, just likea tile mosaic on your kitchen or bathroom wall.

Though a digital photograph looks smooth andcontinuous just like a regular photograph, it's actually

composed of millions of tiny squares as shown below.

On the left the full image, on the right the area in the red square magnified to

show individual pixels


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PIXELS

Each pixel in the image has a numerical value ofbetween 0 and 255 and is made up of three colorchannels. So for example a pixel could be 37-red, 76-

green and 125-blue and it would then look like this If it was 162-red, 27-green and 12-blue, it would look like

this

There are over 16 million possible combinations usingthis scheme and each one represents a different color

Each color in this scheme can be represented by an 8-bitnumber (byte), so the color of each pixel is defined bythree color bytes.


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What is Autofocus?

Autofocus (AF) really could be called power-focus, as it often uses acomputer to run a miniature motorthat focuses the lens for you.

Depending on the distance of the subject from the camera, the lens

has to be a certain distance from the film to form a clear image. In most modern cameras, autofocus is one of a suite of automatic

features that work together to make picture-taking as easy aspossible. These features include:

Automatic film advance Automatic flash

Automatic exposure
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There are two types of autofocus systems:

active and passive. Some cameras may have a

combination of both types, depending on theprice of the camera. In general, less expensive

point-and-shoot cameras use an active system,

while more expensive SLR (single-lens reflex)

cameras with interchangeable lenses use thepassive system.
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Active Auto Focus: In 1986, the Polaroid Corporation used a form of sound navigation

ranging (SONAR), like a submarine uses underwater, to bounce asound wave off the subject.

The Polaroid camera used an ultra-high-frequency sound emitter andthen listened for the echo.

The Polaroid Spectra and later SX-70 models computed the amount oftime it took for the reflected ultrasonic sound wave to reach the camera

and then adjusted the lens position accordingly. But It has its own limitations. Active autofocus on today's cameras uses an infrared signal instead of

sound waves, and is great for subjects within 20 feet Infrared systems use a variety of techniques to judge the distance.

Typical systems might use:

Triangulation Amount of infrared light reflected from the subject Time
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The Advances

A Casio employeedisplays thedigital cameraExilim EX-S880during a pressconference. The

camera featuresa pre-installed

YouTube Capturesoftware to easily

upload videos tothe Web site.


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GPS Photo Taggers

GPS photo taggers let you mark

the location of your photo and if

you upload your geotaggedphotos to Flickr, other people can

see them and where you took

them.


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Instant Photo Printers

Polaroid is teaming with its

spinoff company to make an

instant, ink-free mobile photo

printers. See what you can do

with an iPhone camera next.


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Security Camera within your Camera!

Watch out! Who knows who or what is watching you with that

seemingly unattended iPhone. An iPhone security camera is built

right into your iPhone, but requires some hacking. See how the

police use security cameras next.


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Cameras to solve Crime!

CBI technicians use these camera

setups to photograph recoveredfingerprints to use in comparison and

for running through the AFIS system.


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High Speed Photography

The sound of a gun firing the bullet

actually triggered the flash for this photo,

not the photographer. High-speed

photography can be used to investigate

events such as car wrecks that happenvery quickly.

This photo shows a water balloon just

as it bursts. Notice how the

background of the photograph is

completely dark; a brief flash of light

is the only thing that catches the

image.


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Cameras to Drive at Night

BMW's Night Vision with Pedestrian

Detection system allows drivers to see

what (or who) is down the road -- even

on the darkest nights.


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The EYE Camera!

Stanislavs Bardins of Munich's Ludwig-

Maximilians-University demonstrates the

prototype of a video camera controlled by

the eyes. The camera could be used in

application fields of psychology and

market research.


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digital cameras 061401 siddharth chauhan

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