ImagingDigital

Contents

Capture

Convert

What is digital a image?

ISO Ratings

Bit Depth

Seeing Photography

Composition

1

4

5

8

9

11

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Capture

Digital photography gives

you tools to do just

that; to enhance and

manipulate your images and to

combine them in ways that were

formerly available only to those

with years of experience.

To understand digital imaging,

compare it with conventional

photography. With digital

imaging, instead of exposing and

developing film, you captured

an image by recording a scene

with a digital still camera or

video camera, or you digitize

an existing image by using a

scanner to read the image into

a computer from a conventional

negative, slide, or print.

Instead of a darkroom you

use image editing software such

as Adobe Photoshop to change

the image, either subtly or

dramatically, and then you can

print it out at your desk.

Unlike traditional photography

however, you can also send your

picture by e-mail or display it on

an internet website.

First, an image must be

digitized, that is, converted to

a numerical form that is usable

by the computer and that can

be displayed on the computer’s

monitor. The image that comes

through the lens on your

camera is in analogue form - a

continuously variable scale

of brightness and colour, like

the volume on a stereo, which

changes in smooth gradations

from soft to loud. Similarly, the

image on a conventional slide

or negative has a continuous

scale of tones, with unbroken

gradations from light to dark.

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Convert

pixels are too small to be seen,

and the eye perceives the image

in continuous tones.

For digital imaging, an image is

recorded in a grid of pixels or

picture elements. Ordinarily, the

For computer use, the

image is converted to

digital form by using

CCDs (charge-coupled devices).

A digital camera’s recording

chip contains millions of light-

sensitive CCD cells arranged

in a grid, like squares on a

sheet of graph paper. CMOS

(complementary metal-oxide

semiconductor) technology

performs the same function.

A scanner that digitizes an

existing photograph uses a line

of CCD cells that record one row

at a time to assemble the same

kind of grid. Each position on

the grid is recorded on a pixel, a

square with a uniform brightness

and colour. Each value and its

position is saved and transmitted

as a series of numbers.

The computer can reassemble

the grid from these numbers

and display it on a monitor or

send it to a printer.

When the grid is very fine,

the pixels are very small –

your eye perceives an image

in continuous tones, just as it

would in a film–based photo.

The finer the resolution is, the

larger the number of pixels

needed to complete the image.

Whether you plan to

work on a photograph taken

with a digital camera or one

scanned into digital form

from a traditional print, slide

or negative, you will want to

understand the relationship

between file size and resolution

(the fineness of detail) in your

final image.

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What is a digital image?

A digital image is like a

site of coloured tiles

that creates a realistic

scene in a mosaic. The more tiles

in the mosaic, the more detail

is possible in the scene. Each

pixel in an image is one tile in

the mosaic; the image file size

corresponds to the total number

of tiles.

Image size is the physical size

of a photograph, like the surface

where the mosaic is being

installed – a one-foot-square on

a bathroom wall, for example.

Resolution is the number

of pixels (or tiles) per unit of

length, in pixels per inch (or tiles

per foot). If your resolution is

four tiles per foot, the tiles must

be three-inches-square. You will

need 16 tiles (four tiles by four)

to fill the one-square-foot space.

If you kept the space the

same size but used smaller

tiles – say one-inch-square – you

could make a design with much

finer detail, but then you would

need 144 more tiles. Finer detail

demands a larger file.

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For the same image size,

higher resolution looks finer

but requires more pixels. You

need to know how large you

want your image to be (image

size) and how much details you

need (resolution) in order to

determine how many pixels (file

size) will be required.

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ISO Ratings

A digital camera often let

you select the ISO rating

for each shot. Using a

higher ISO can be an advantage

that lets you shoot in lower light,

but just as graininess becomes

more visible with high-speed

films, random specks called noise

occur more often in a digital

image as you increase the ISO.

You do not need colour

correcting filters when you

use a digital camera. Some

cameras adjust for the light

source automatically. With

others you select the kind

of light – daylight, tungsten,

fluorescent, cloudy or flash – so

colours are rendered normally.

The lens focal length may

give you an unexpected angle

of view. Many cameras capture

pictures on a CCD or CMOS

chip that is smaller than the

traditional 35mm film frame.

So to provide the same angle

of view as a lens on a 35mm

camera, the lens focal length

on most digital cameras is

somewhat shorter.

Most manufacturers of

digital cameras publish a

‘35mm equivalent’ focal that,

if you are familiar with 35mm

cameras, helps you to know

what will appear in the frame.

Keep in mind that shorter lenses

give you more depth of field

regardless the frame size.

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Bit : Smallest unit of digital information

Byte : 8 bits

Kilobyte (K or KB) : 1,000 bytes

Megabyte (MB) : 1,000,000 bytes

Gigabyte (GB) : 1,000,000,000 bytes

Terabyte (TB) : 1,000.000.000.000 bytes

Bit Depth

Computers record

information in binary

form using combinations

of the digits one (1) and zero

(0). A Bit is the smallest unit of

information, consisting of either a

one or a zero, so it can represent

only two different possibilities

– yes or no, black or white, on

or off. A byte is an eight-bit

sequence that can represent

28 (or 256) possibilities, such as

black, white, and 254 different

shades of grey in between.

The size of an image file is the

number of bytes that it contains.

The amount of information in

a digital image – and therefore its

technical quality – is determined

by both the number of pixels

and the number of possible

values each pixel can hold. The

greater the numbers of pixels

that represent a given image, the

greater the amount of detail that

can be recorded. In two pictures

of the same size, one with smaller

(and therefore more) pixels can

hold finer pictorial detail.

Similarly, the more finely

divided the colours and tones

in each pixel (the bit depth

or number of bits per pixel),

each pixel can render a greater

selection of possible colours and

tones. Many other factors affect

quality, but in general, the more

data for an image, the better the

final photography will be.

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1 bit per pixel gives two colours. The image can have only

two tones: usually black and white.

8 bits per pixel gives 256 tones. From 0 (black) to 255

(white), 256 tones provide excellent black-and-white rendi-

tion but are not enough for good colour.

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24 bits per pixel gives 16,777,216 tones, enough for a

colour image with smooth gradations and full tonality,

comparable to traditional colour film photography.

Colour photography is made up of three images, one

in each of the three primary colours. With 8 bits each,

those three colours (red, blue, green) can each have

256 different shades – red from darkest to lightest for

example – making more than 16 million possible colours.

Seeing Photographs

How do you learn to make better picture?

Every time you make

an exposure you

make choices, either

deliberately or accidentally.

Do you show the whole

scene or just a detail? Do you

make everything sharp from

foreground to background or

have only part of the scene in

focus? Do you use a fast shutter

The scene is then at least

reduced to a smaller size

and confined within the

edges of the picture doormat,

just as it will be in the print. As

you look through the viewfinder,

imagine you are looking at

a print, but one that you can

still change. You can eliminate

a distracting background by

making it out of focus by

changing your position to a better

angle, and so on. Try to see how

Framing the picture

a picture communicates its visual

content. Photography transforms

a three-dimensional event into a

frozen instant, reduced in size on

a flat piece of paper. The event is

abstracted, and even if you were

there and can remember how it

“really” was, the image in front

of you is the tangible remaining

object. This concentration on

the actual image will help you

visualise scenes as photographs

when you are shooting.

speed to freeze motion sharply

or a slow shutter speed to blur

it? Your first step is to see your

options, to see the potential

photographs in front of your

camera. Before you make an

exposure, try to visualise the

way the scene will look as a

print. Looking through the

viewfinder helps.

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One of your first choices

is how much of a scene

to show. Whether the

subject is a person, a building,

or a tree, beginners often are

reluctant to show anything less

than the whole thing. People often

photograph a subject in its entirety

– Grandpa is shown from head to

toe, even if that makes his head so

small that you can’t see his face

for the intensity and immediacy

of his images. This simple piece

of advice can help most beginner

photographers improve their

work. Getting closer eliminates

distracting objects and simplifies

the contents of a picture. It

reduces the confusion of busy

backgrounds, focuses attention on

the main subject, and lets you see

expressions on people’s faces.

clearly. In many cases, however,

it was a particular aspect of the

subject that got the photographer’s

attention in the first place, perhaps

the expression on the face of the

person, the peeling paint on the

building or a bent branch of the

tree. Get closer to subject. “If your

pictures aren’t good enough, you

aren’t close enough,’” said Robert

Capa, a war photographer known

John Capa

The Battle Begins

An American soldier landing on

Omaha Beach, D-day, June 1944

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Composition

What is your photography about?

Instead of shooting right away,

stop a moment to decide which

part of a scene you really want

to show. You might want to take

one picture of the whole scene,

then try a few details.

Sometimes you won’t want to

move closer, as in photographing

a prairie landscape where the

spacious expanse of land and

sky is important or in making an

environmental portrait where the

setting reveals something about

the person.

Try to visualise what you want

the photograph to look like.

Then move around as you look

through the viewfinder. Examine

the edges of the image frame.

Do they enclose or cut into the

subject the way you want? In

time these decisions come more

intuitively, but it is useful at first

to work through them deliberately.

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Arthur Siegel

Right of Assembly 1939

Siegel shot from a high vantage

point to get in as much of

this street demonstration as

possible. He wanted to show each

demonstrator as an individual

expressing a common belief, so he

filled the frame with them and tried

to get them all in sharp focus.

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Jerome Liebling

Cop’s Hat Union Square New York 1948

very shallow depth of field. In the

entire shot only the policeman’s

hat is in focus and the eye is drawn

to it instantly. A very small part of

an image, like the badge, can carry

considerable symbolic weight.

A detail of a scene can

tell as much as and

sometimes more than

an overall shot. Liebling shot

from below eye level, a humble

vantage point, and intentionally

used a very wide aperture to get

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Combining different

elements in a scene

can bring order out of

chaos or sometimes a sense

of dislocation to ordinary. Lee

Friedlander wrote, “The camera is

not merely a reflecting pool…The

Lee Friedlander

Route 9W New York 1959

mind finger presses the release

on the silly machine and it stops

time and holds what its jaws can

encompass the light will stain.

That moment when landscape

speaks to the observer.”

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