Photography (derived from the Greek photos- for "light" and -graphos for
"drawing") is the art, science, and practice of creating durable images by recording
light or other electromagnetic radiation, either chemically by means of a lightsensitive material such as photographic film, or electronically by means of an
Typically, a lens is used to focus the light reflected or emitted from objects into a
real image on the light-sensitive surface inside a camera during
a timed exposure. The result in an electronic image sensor
is an electrical charge at each pixel, which is electronically
processed and stored in a digital image file for subsequent
display or processing. The result in a photographic emulsion
is an invisible latent image, which is later chemically developed
into a visible image, either negative or positive depending on the
purpose of the photographic material and the method of processing.
A positive is a film or paper record of a
scene that represents the color and
luminance of objects in that scene with
the same colors and luminances (as
near as the medium will allow). Color
transparencies are an example of
positive photography: the range of
colors presented in the medium is
limited by the tonal range of the
original image (dark and light areas
In photography, a negative is an image,
usually on a strip or sheet of transparent
plastic film, in which the lightest areas of
the photographed subject appear darkest
and the darkest areas appear lightest. This
reversed order occurs because of the
extremely light-sensitive chemicals a
camera film must use to capture an image
quickly enough for ordinary picture-taking,
which are darkened, rather than bleached,
by exposure to light and subsequent
What is a darkroom?
A darkroom is a room that can be made completely dark to allow the
processing of light sensitive photographic materials, including
photographic film and photographic paper. Darkrooms have been created
and used since the inception of photography in the early 19th century.
Due to the popularity of color photography and complexity of processing
color film (see C-41 process) and printing color photographs and also to
the rise, first of Polaroid technology and later digital photography,
darkrooms are decreasing in popularity, though are still commonplace on
college campuses, schools and in the studios of many professional
Other applications of darkrooms include the use in nondestructive testing,
such as magnetic particle inspection.
In most darkrooms, an enlarger, an optical apparatus similar to a slide
projector, that projects the image of a negative onto a base, finely controls the
focus, intensity and duration of light, is used for printmaking. A sheet of
photographic paper is exposed to the enlarged image from the negative.
When making black-and-white prints, a safelight is commonly used to
illuminate the work area. Since the majority of black-and-white papers are
sensitive to only blue, or to blue and green light, a red- or amber-colored light
can be safely used without exposing the paper. Color print paper, being
sensitive to all parts of the visible spectrum, must be kept in complete darkness
until the prints are properly fixed.
Another use for a darkroom is to load film in and out of cameras, development
spools, or film holders, which requires complete darkness.
During exposure, values in the image can be adjusted, most often by "dodging"
(reducing the amount of light to a specific area of an image by selectively blocking
light to it for part or all of the exposure time) and/or "burning" (giving additional
exposure to specific area of an image by exposing only it while blocking light to the
rest). Filters, usually thin pieces of colored plastic, can be used to increase or
decrease an image's contrast (the difference between dark tones and light tones).
After exposure, the photographic printing paper (which still appears blank) is ready
to be processed.
Photographers generally begin printing a roll of film by making a contact print of
their negatives to use as a quick reference to decide which images to enlarge. The
paper that has been exposed is processed, first by immersion in a photographic
developer, halting development with a stop bath, and fixing in a photographic fixer.
The print is then washed to remove the processing chemicals and dried.