Tpp Digital Photography

8/8/2019 Tpp Digital Photography

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DIGITAL PHOTOGRAPHY

. JIGAR MEHTA

Phone:9819854452 email: [email protected] RAIT(extc)

.AMEY KELKAR

Phone:9869075044 email:[email protected] RAIT(extc)


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ABSTRACTIn the past twenty years, most of the major technological breakthroughs in

consumer electronics have really been part of one larger breakthrough. When

you get down to it, CDs, DVDs, HDTV, MP3s and DVRs are all built around the

same basic process: converting conventional analog information (represented by

a fluctuating wave) into digital information (represented by ones and zeros, or

bits). This fundamental shift in technology totally changed how we handle visual

and audio information -- it completely redefined what is possible.

The digital camera is one of the most remarkable instances of this shift.

The digital camera is not something of a magic box that came out of the blue and

made wonders. Digital photography has many advantages over traditional film

photography. Digital photos are convenient, allow you to see the results instantly,

don't require the costs of film and developing, and are suitable for software

editing and uploading to the Internet. While shooting on film will always have a

place in the world of photography, digital models have taken over the consumer

camera market almost completely
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Basic working

The image needs to be represented in the language that computers recognizes --

bits and bytes. Essentially, a digital image is just a long string of 1s and 0s that

represent all the tiny colored dots -- or pixels -- that collectively make up the

image. The following options are available:

We can take a photograph using a conventional film camera, process the

film chemically, print it onto photographic paper and then use a digital

scannerto sample the print (record the pattern of light as a series of pixel

values).

We can directly sample the original light that bounces off our subject,

immediately breaking that light pattern down into a series of pixel values --

in other words, we can use a digital camera.

A Filmless Camera

Instead of film, a digital camera has a sensor that

converts light into electrical charges.

The image sensor employed by most digital

cameras is a charge coupled device (CCD).

Some cameras use complementary metal oxide

semiconductor (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 millions of tiny solar cells.

Once the sensor converts the light into electrons, it reads the value (accumulated

charge) of each cell in the image. This is where the differences between the two

main sensor types kick in:

A CCD transports the charge across the chip and reads it at one corner of

the array. An analog-to-digital converter (ADC) then turns each pixel's

A CMOS image sensor
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value into a digital value by measuring the amount of charge at each

photo site and converting that measurement to binary form.

CMOS devices use several transistors at each pixel to amplify and move

the charge using more traditional wires. The CMOS signal is digital, so it

needs no ADC.

Differences between the two types of sensors lead

to a number of pros and cons:

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 located next 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 as

much as 100 times more power than an equivalent CMOS sensor.

CCD sensors have been mass produced for a longer period of time, so

they are more mature. They tend to have higher quality pixels, and more

of them.

Although numerous differences exist between the two sensors, they both play the

same role in the camera -- they turn light into electricity. For the purpose of

understanding how a digital camera works, we can think of them as nearly

identical devices.

Resolution

The amount of detail that the camera can capture is called the resolution, and it

is measured in pixels. The more pixels a camera has, the more detail it can

capture and the larger pictures can be without becoming blurry or "grainy."

A CCD sensor


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Some typical resolutions include:

256x256 - Found on very cheap cameras, this resolution is so low that the

picture quality is almost always unacceptable. This is 65,000 total pixels.

640x480 - This is the low end on most "real" cameras. This resolution is

ideal for e-mailing pictures or posting pictures on a Web site.

1216x912 - This is a "mega pixel" image size -- 1,109,000 total pixels --

good for printing pictures.

1600x1200 - With almost 2 million total pixels, this is "high resolution."

You can print a 4x5 inch print taken at this resolution with the same quality

that you would get from a photo lab.

2240x1680 - Found on 4 mega pixel cameras -- the current standard --this allows even larger printed photos, with good quality for prints up to

16x20 inches.

4064x2704 - A top-of-the-line digital camera with 11.1 mega pixels takes

pictures at this resolution. At this setting, you can create 13.5x9 inch prints

with no loss of picture quality.

Photo courtesy Morgue file

The size of an image taken at different resolutions
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High-end consumer cameras can capture over 12 million pixels. Some

professional cameras support over 16 million pixels, or 20 million pixels for large-

format cameras. For comparison, Hewlett Packard estimates that the quality of

35mm film is about 20 million pixels

Capturing Color

As a continuation of the above lines, it can be further investigated that the

sensor array is basically a microchip about 10 mm across. Every image sensor is

a charged-couple device (CCD) converting light into electric charges, and is

essentially a silicon chip used to measure light. These charges are stored as

analog data that are then converted to digital via a device called an analog to

digital converter (ADC). Over the chip are present a collection of very small light-

sensitive diodes, named photosites, or pixels that convert light (or more

scientifically, photons) into electrical charges called electrons. The pixels are very

much light sensitive, therefore with brighter light striking them, produces greater

build up of electrical charges. Each 1000 array receptor creates 1 pixel, and

every pixel corresponds to some information stored. The light enters the digitalcamera via the lens, which is the same mechanism as the conventional analog

camera. And this light hits the CCD when the photographer presses the shutter

button. The shutter opens and thereby illuminates every pixel, however with

various intensities.

Taking a look apart, it can be observed that quite a few digital cameras use

CMOS (meaning complementary metal oxide semiconductor, a technology of

manufacturing these microchips) technology based microchips as image

sensors. The basic advantage is that the CMOS sensors are appreciably

cheaper and simpler to fabricate than CCDs. Another great advantage from

CMOS sensors is that these take very less power compared to other technology,

which adds up to the fact as to their extensive use, and can thus even support


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the implementation of additional circuitry on the same chip like ADC, some

control units etc. Thus it can be stated that CMOS technology based cameras

are small, light, cheap and also energy efficient, yet at the cost of some amount

of image quality.

However the common trend remains that all cameras of the mega pixel range

and higher up use CCD chips instead of CMOS. This is because of the fact of

picture quality only, leaving aside the price differences.

Each photo site is colorblind. It only keeps track of the total intensity of the light

that strikes its surface. In order to get a full color image, most sensors use

filtering to look at the light in its three primary colors. Once the camera records all

three colors, it combines them to create the full spectrum.

There are several ways of recording the three colors in a digital camera. The

highest quality cameras use three separate sensors, each with a different filter. A

beam splitterdirects light to the different sensors. Think of the light entering the

camera as water flowing through a pipe. Using a beam splitter would be like

dividing an identical amount of water into three different pipes. Each sensor gets

an identical look at the image; but because of the filters, each sensor onlyresponds to one of the primary colors.


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How the original (left) image is split in a beam

splitter

The advantage of this method is that the camera records each of the three colors

at each pixel location. Unfortunately, cameras that use this method tend to be

bulky and expensive.

Another method is to rotate a series of red, blue and green filters in front of a

single sensor. The sensor records three separate images in rapid succession.

This method also provides information on all three colors at each pixel location;

but since the three images aren't taken at precisely the same moment, both the

camera and the target of the photo must remain stationary for all three readings.

This isn't practical for candid photography or handheld cameras.

Both of these methods work well for professional studio cameras, but they're not

necessarily practical for casual snapshots. A more economical and practical way

to record the primary colors is to permanently place a filter called a color filter

array over each individual photo site. By breaking up the sensor into a variety of

red, blue and green pixels, it is possible to get enough information in the general

vicinity of each sensor to make very accurate guesses about the true color at that


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location. This process of looking at the other pixels in the neighborhood of a

sensor and making an educated guess is called interpolation.

The most common pattern of filters is the Bayer filter pattern. This pattern

alternates a row of red and green filters with a row of blue and green filters. The

pixels are not evenly divided -- there are as many green pixels as there are blue

and red combined. This is because the human eye is not equally sensitive to all

three colors. It's necessary to include more information from the green pixels in

order to create an image that the eye will perceive as a "true color."

The advantages of this method are that only one sensor is required, and all the

color information (red, green and blue) is recorded at the same moment. That

means the camera can be smaller, cheaper, and useful in a wider variety of

situations. The raw output from a sensor with a Bayer filter is a mosaic of red,

green and blue pixels of different intensity.

Digital cameras use specialized demos icing algorithms to convert this mosaic

into an equally sized mosaic of true colors. The key is that each colored pixel can
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be used more than once. The true color of a single pixel can be determined by

averaging the values from the closest surrounding pixels.

Some single-sensor cameras use alternatives to the Bayer filter pattern. X3

technology, for example, embeds red, green and blue photo detectors in silicon.

Some of the more advanced cameras subtract values using the typesetting

colors cyan, yellow, green and magenta instead of blending red, green and blue.

There is even a method that uses two sensors. However, most consumer

cameras on the market today use a single sensor with alternating rows of

green/red and green/blue filters

Exposure and Focus

Just as with film, a digital camera has to control the amount of light that reaches

the sensor. The two components it uses to do this, the aperture and shutter

speed, are also present on conventional cameras.

Aperture: The size of the opening in the camera. The aperture is

automatic in most digital cameras, but some allow manual adjustment to

give professionals and hobbyists more control over the final image.

Shutter speed: The amount of time that light can pass through theaperture. Unlike film, the light sensor in a digital camera can be reset

electronically, so digital cameras have a digital shutter rather than a

mechanical shutter.

These two aspects work together to capture the amount of light needed to make

a good image. In photographic terms, they set the exposure of the sensor. In

addition to controlling the amount of light, the camera has to adjust the lenses to

control how the light is focused on the sensor. In general, the lenses on digital

cameras are very similar to conventional camera lenses -- some digital cameras

can even use conventional lenses. Most use automatic focusing techniques.

The focal length, however, is one important difference between the lens of a

digital camera and the lens of a 35mm camera. The focal length is the distance
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between the lens and the surface of the sensor. Sensors from different

manufacturers vary widely in size, but in general they're smaller than a piece of

35mm film. In order to project the image onto a smaller sensor, the focal length is

shortened by the same proportion.

Focal length also determines the magnification, or zoom, when you look through

the camera. In 35mm cameras, a 50mm lens gives a natural view of the subject.

Increasing the focal length increases the magnification, and objects appear to get

closer. The reverse happens when decreasing the focal length. A zoom lens is

any lens that has an adjustable focal length, and digital cameras can have optical

or digital zoom -- some have both. Some cameras also have macro focusing

capability, meaning that the camera can take pictures from very close to thesubject.

Types of lenses

Digital cameras have one of four types of lenses:

Fixed-focus, fixed-zoom lenses - These are the kinds of lenses on

disposable and inexpensive film cameras -- inexpensive and great for

snapshots, but fairly limited.

Optical-zoom lenses with automatic focus - Similar to the lens on a

video camcorder; these have "wide" and "telephoto" options and automatic

focus. The camera may or may not support manual focus. These actually

change the focal length of the lens rather than just magnifying the

information that hits the sensor.

Digital-zoom lenses - With digital zoom, the camera takes pixels from the

center of the image sensor and interpolates them to make a full-sized

image. Depending on the resolution of the image and the sensor, this

approach may create a grainy or fuzzy image. we can manually do the

same thing with image processing software -- simply snap a picture, cut

out the center and magnify it.


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Replaceable lens systems - These are similar to the replaceable lenses

on a 35mm camera. Some digital cameras can use 35mm camera lenses

Storage

Most digital cameras have an LCD screen, so we can view your picture right

away. This is one of the great advantages of a digital camera -- we get

immediate feedback on what you capture. Of course, viewing the image on your

camera would lose its charm if that's all you could do. We want to be able to load

the picture into your computer or send it directly to

a printer. There are several ways to do this.

Early generations of digital cameras had fixed

storage inside the camera. You needed to connect

the camera directly to a computer with cables to

transfer the images. Although most of today's

cameras are capable of connecting through serial,

parallel, SCSI, USB orFireWire connections, they

usually also use some sort of removable storagedevice.

Digital cameras use a number of storage systems. These are like reusable,

digital film, and they use a caddy or card reader to transfer the data to a

computer. Digital camera manufacturers often develop their own proprietary flash

memory devices, including Smart Media cards, Compact Flash cards and

Memory Sticks. Some other removable storage devices include:

Floppy disks

Hard disks, or micro drives

Writeable CDs and DVDs

A Compact Flash card
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No matter what type of storage they use, all digital cameras need lots of room for

pictures. They usually store images in one of two formats -- TIFF, which is

uncompressed, and JPEG, which is compressed. Most cameras use the JPEG

file format for storing pictures, and they sometimes offer quality settings (such as

medium or high). The following chart will gives us an idea of the file sizes you

might expect with different picture sizes.

Image SizeTIFF

(uncompressed)

JPEG

(high

quality)

JPEG

(medium

quality)

640x480 1.0 MB 300 KB 90 KB

800x600 1.5 MB 500 KB 130 KB

1024x768 2.5 MB 800 KB 200 KB

1600x1200 6.0 MB 1.7 MB 420 KB

To make the most of their storage space, almost all digital cameras use some

sort ofdata compression to make the files smaller. Two features of digital images

make compression possible. One is repetition. The other is irrelevancy.

Imagine that throughout a given photo, certain patterns develop in the colors.For example, if a blue sky takes up 30 percent of the photograph, we can be

certain that some shades of blue are going to be repeated over and over again.

When compression routines take advantage of patterns that repeat, there is no

loss of information and the image can be reconstructed exactly as it was

recorded. Unfortunately, this doesn't reduce files any more than 50 percent, and

sometimes it doesn't even come close to that level.

Irrelevancy is a trickier issue. A digital camera records more information than the

human eye can easily detect. Some compression routines take advantage of this

fact to throw away some of the more meaningless data.
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Summary of working

It takes several steps for a digital camera to take a picture. Here's a review of

what happens in a CCD camera, from beginning to end:

We aim the camera at the subject and adjust the optical zoom to get

closer or farther away.

Press lightly on the shutter release.

The camera automatically focuses on the subject and takes a reading of

the available light.

The camera sets the aperture and shutter speed for optimal exposure.

press the shutter release all the way.

The camera resets the CCD and exposes it to the light, building up anelectrical charge, until the shutter closes.

The ADC measures the charge and creates a digital signal that represents

the values of the charge at each pixel.

A processor interpolates the data from the different pixels to create natural

color. On many cameras, it is possible to see the output on the LCD at this

stage.

A processor may perform a preset level of compression on the data.

The information is stored in some form of memory device (probably a

Flash memory card).

Basic attributes of a digital camera
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The basic attribute of a digital camera that determines image quality is its mega

pixel rating . This number refers to the amount of information that the camera

sensor can capture in a single photograph. Cameras with high mega pixel ratings

take larger pictures with more detail.

There are many additional features available on digital cameras, including image

stabilization, on-board image editing, and color correction functions, auto-

bracketing and burst modes. A lot of these can be handled by image editing

software, and so they can be unnecessary (and often inferior) when built into a

camera. Burst mode, macro mode and image stabilization are probably the most

useful extra features

Camera Settings and Modes

With a decent digital camera and a bit of practice, anyone can take acceptable

quality photos with the camera set on full automatic..

When we are changing the settings on a camera, we are trying to find the proper

exposure for the subject and lighting conditions. Exposure is the amount of light

hitting the camera's sensor when you take a photo. Generally, we will want the

exposure set so that the image captured by the camera's sensor closely matches

what you see with our eyes.The camera tries to accomplish this when it's on full

automatic mode, but the camera is easily fooled and a little slow, which is why

manual settings usually produce better pictures.

To adjust exposure, we can tweak two different settings: aperture and shutter

speed. Aperture is the diameter of the lens opening a wider aperture meansmore light gets through. Aperture is measured in f-stops. Higher f-stop numbers

mean a smaller aperture. The aperture setting also affects depth of field, the

amount of the photograph that is in focus.


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Smaller apertures (higher f-stops) give longer depth of field. A person in the

foreground and the cars 20 feet behind her could all be in focus with a small

enough aperture. A larger aperture results in a shallow depth of field, which you

normally use for close-up shots and portraits.

Our digital camera set at its fastest shutter speed

-- 1/4000 of a second.

Shutter speed is the amount of time the shutter remains open to allow light

through it. An extremely fast shutter speed is 1/2000 of a second, while camera

settings usually allow up to about one second, which is very slow. One-sixtieth of

a second is about as slow a shutter speed as you can use when taking a hand-

held shot, and not get any blur. Some photographers force their camera shutters

to stay open for much longer to create various special effects. Leaving a camera

pointed at the night sky with the shutter open for several hours results in a photo

of the paths the stars seem to take across the sky as the Earth rotates. While a

slow shutter speed lets in more light, it also makes it very difficult to get a crisp

picture. Any movement at all (of either the subject or the camera) will result in

blurring. Sometimes you might want this effect, but for a clear photo of a moving

object, you need a fast shutter speed.


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Our digital camera set at its slowest shutter speed

-- 1/30 of a second.

Conclusion

The turnover in this field has been major.Today further research and

development is taking place at a tremendous pace.This is all due to the

immense acceptance of digital image technology in markets worldwide.Efforts

are being made to utilize holograms with the image processing field so as to

create 3-dimensional images of the pictures taken. It is only a matter of time now

that, we would be able to see a life size 3D image of our dear ones who aresomewhere across the globe!


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References

Digital image processing and photography

--- By Jacob Jelling

Images digitized : an overview

--- IEEE journals

Passion for pixels

--- By Bob Stanley

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