Digital
Imaging
Contents Capture
1
Convert
4
What is digital a image?
5
ISO Ratings
8
Bit Depth
9
Seeing Photography
11
Composition
13
Capture
D
igital photography gives
dramatically, and then you can
you tools to do just
print it out at your desk.
that; to enhance and
however, you can also send your
combine them in ways that were
picture by e-mail or display it on
formerly available only to those
an internet website.
with years of experience. To understand digital imaging,
1 Digital Imaging
Unlike traditional photography
manipulate your images and to
First, an image must be digitized, that is, converted to
compare it with conventional
a numerical form that is usable
photography. With digital
by the computer and that can
imaging, instead of exposing and
be displayed on the computer’s
developing film, you captured
monitor. The image that comes
an image by recording a scene
through the lens on your
with a digital still camera or
camera is in analogue form - a
video camera, or you digitize
continuously variable scale
an existing image by using a
of brightness and colour, like
scanner to read the image into
the volume on a stereo, which
a computer from a conventional
changes in smooth gradations
negative, slide, or print.
from soft to loud. Similarly, the
Instead of a darkroom you
image on a conventional slide
use image editing software such
or negative has a continuous
as Adobe Photoshop to change
scale of tones, with unbroken
the image, either subtly or
gradations from light to dark.
Convert
F
or computer use, the
The computer can reassemble
image is converted to
the grid from these numbers
digital form by using
and display it on a monitor or
CCDs (charge-coupled devices). A digital camera’s recording
send it to a printer. When the grid is very fine,
chip contains millions of light-
the pixels are very small –
sensitive CCD cells arranged
your eye perceives an image
in a grid, like squares on a
in continuous tones, just as it
sheet of graph paper. CMOS
would in a film–based photo.
(complementary metal-oxide
The finer the resolution is, the
semiconductor) technology
larger the number of pixels
performs the same function.
needed to complete the image.
A scanner that digitizes an
Whether you plan to
existing photograph uses a line
work on a photograph taken
of CCD cells that record one row
with a digital camera or one
at a time to assemble the same
scanned into digital form
kind of grid. Each position on
from a traditional print, slide
the grid is recorded on a pixel, a
or negative, you will want to
square with a uniform brightness
understand the relationship
and colour. Each value and its
between file size and resolution
position is saved and transmitted
(the fineness of detail) in your
as a series of numbers.
final image.
For digital imaging, an image is
pixels are too small to be seen,
recorded in a grid of pixels or
and the eye perceives the image
picture elements. Ordinarily, the
in continuous tones.
Digital Imaging
4
What is a digital image? site of coloured tiles
A
of a photograph, like the surface
need 16 tiles (four tiles by four)
that creates a realistic
where the mosaic is being
to fill the one-square-foot space.
scene in a mosaic. The more tiles
installed – a one-foot-square on
in the mosaic, the more detail
a bathroom wall, for example.
is possible in the scene. Each
Resolution is the number
digital image is like a
5 Digital Imaging
Image size is the physical size
be three-inches-square. You will
If you kept the space the same size but used smaller tiles – say one-inch-square – you
pixel in an image is one tile in
of pixels (or tiles) per unit of
could make a design with much
the mosaic; the image file size
length, in pixels per inch (or tiles
finer detail, but then you would
corresponds to the total number
per foot). If your resolution is
need 144 more tiles. Finer detail
of tiles.
four tiles per foot, the tiles must
demands a larger file.
For the same image size,
size) and how much details you
higher resolution looks finer
need (resolution) in order to
but requires more pixels. You
determine how many pixels (file
need to know how large you
size) will be required.
want your image to be (image Digital Imaging
6
ISO Ratings
A
digital camera often let
cameras adjust for the light
of view as a lens on a 35mm
you select the ISO rating
source automatically. With
camera, the lens focal length
for each shot. Using a
others you select the kind
on most digital cameras is
higher ISO can be an advantage
of light – daylight, tungsten,
somewhat shorter.
that lets you shoot in lower light,
fluorescent, cloudy or flash – so
but just as graininess becomes
colours are rendered normally.
Most manufacturers of digital cameras publish a
The lens focal length may
‘35mm equivalent’ focal that,
films, random specks called noise
give you an unexpected angle
if you are familiar with 35mm
occur more often in a digital
of view. Many cameras capture
cameras, helps you to know
image as you increase the ISO.
pictures on a CCD or CMOS
what will appear in the frame.
You do not need colour
more visible with high-speed
chip that is smaller than the
Keep in mind that shorter lenses
correcting filters when you
traditional 35mm film frame.
give you more depth of field
use a digital camera. Some
So to provide the same angle
regardless the frame size.
Digital Imaging
8
Bit Depth
C
omputers record
shades of grey in between.
of the same size, one with smaller
information in binary
The size of an image file is the
(and therefore more) pixels can
form using combinations
number of bytes that it contains.
hold finer pictorial detail.
of the digits one (1) and zero
The amount of information in
(0). A Bit is the smallest unit of
a digital image – and therefore its
divided the colours and tones
information, consisting of either a
technical quality – is determined
in each pixel (the bit depth
one or a zero, so it can represent
by both the number of pixels
or number of bits per pixel),
only two different possibilities
and the number of possible
each pixel can render a greater
– yes or no, black or white, on
values each pixel can hold. The
selection of possible colours and
or off. A byte is an eight-bit
greater the numbers of pixels
tones. Many other factors affect
sequence that can represent
that represent a given image, the
quality, but in general, the more
28 (or 256) possibilities, such as
greater the amount of detail that
data for an image, the better the
black, white, and 254 different
can be recorded. In two pictures
final photography will be.
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
9
Digital Imaging
Similarly, the more finely
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 rendition but are not enough for good colour.
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.
Digital Imaging 10
Seeing Photographs How do you learn to make better picture?
E
very time you make
speed to freeze motion sharply
an exposure you
or a slow shutter speed to blur
make choices, either
it? Your first step is to see your
deliberately or accidentally.
options, to see the potential
Do you show the whole
photographs in front of your
scene or just a detail? Do you
camera. Before you make an
make everything sharp from
exposure, try to visualise the
foreground to background or
way the scene will look as a
have only part of the scene in
print. Looking through the
focus? Do you use a fast shutter
viewfinder helps.
Framing the picture
T
11 Digital Imaging
he scene is then at least
a picture communicates its visual
reduced to a smaller size
content. Photography transforms
and confined within the
a three-dimensional event into a
edges of the picture doormat,
frozen instant, reduced in size on
just as it will be in the print. As
a flat piece of paper. The event is
you look through the viewfinder,
abstracted, and even if you were
imagine you are looking at
there and can remember how it
a print, but one that you can
“really� was, the image in front
still change. You can eliminate
of you is the tangible remaining
a distracting background by
object. This concentration on
making it out of focus by
the actual image will help you
changing your position to a better
visualise scenes as photographs
angle, and so on. Try to see how
when you are shooting.
O
ne of your first choices
clearly. In many cases, however,
for the intensity and immediacy
is how much of a scene
it was a particular aspect of the
of his images. This simple piece
to show. Whether the
John Capa The Battle Begins
subject that got the photographer’s
of advice can help most beginner
An American soldier landing on
subject is a person, a building,
attention in the first place, perhaps
photographers improve their
Omaha Beach, D-day, June 1944
or a tree, beginners often are
the expression on the face of the
work. Getting closer eliminates
reluctant to show anything less
person, the peeling paint on the
distracting objects and simplifies
than the whole thing. People often
building or a bent branch of the
the contents of a picture. It
photograph a subject in its entirety
tree. Get closer to subject. “If your
reduces the confusion of busy
– Grandpa is shown from head to
pictures aren’t good enough, you
backgrounds, focuses attention on
toe, even if that makes his head so
aren’t close enough,’” said Robert
the main subject, and lets you see
small that you can’t see his face
Capa, a war photographer known
expressions on people’s faces. Digital Imaging 12
Composition What is your photography about?
I
nstead of shooting right away,
setting reveals something about
stop a moment to decide which
the person.
part of a scene you really want
to show. You might want to take
the photograph to look like.
one picture of the whole scene,
Then move around as you look
then try a few details.
through the viewfinder. Examine
Sometimes you won’t want to
13
Digital Imaging
Try to visualise what you want
the edges of the image frame.
move closer, as in photographing
Do they enclose or cut into the
a prairie landscape where the
subject the way you want? In
spacious expanse of land and
time these decisions come more
sky is important or in making an
intuitively, but it is useful at first
environmental portrait where the
to work through them deliberately.
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.
Digital Imaging 14
Jerome Liebling Cop’s Hat Union Square New York 1948
A
detail of a scene can
very shallow depth of field. In the
tell as much as and
entire shot only the policeman’s
sometimes more than
hat is in focus and the eye is drawn
an overall shot. Liebling shot
to it instantly. A very small part of
from below eye level, a humble
an image, like the badge, can carry
vantage point, and intentionally
considerable symbolic weight.
used a very wide aperture to get
15
Digital Imaging
Lee Friedlander Route 9W New York 1959
C
ombining different
mind finger presses the release
elements in a scene
on the silly machine and it stops
can bring order out of
time and holds what its jaws can
chaos or sometimes a sense
encompass the light will stain.
of dislocation to ordinary. Lee
That moment when landscape
Friedlander wrote, “The camera is
speaks to the observer.”
not merely a reflecting pool…The
Digital Imaging 16