ORIGINALS 2 The originals can be classified into three major
groups: Line originals Tone originals Color originals
Slide 3
ORIGINALS 3 Line originals: Picture in solid black images on a
white background eg. Pen and ink drawings Tone originals: Pictures
in black and white, but with intermediate areas of varying density
eg. Photographic prints, chalk drawings, pencil sketches and wash
drawings Color originals: Pictures presenting in line and tone in
color eg. Color transparencies
Slide 4
LINE ORIGINALS 4 Line originals must be presented in only in
two pieces: dense, opaque black and clean, reflective white The
requirements: 1. All image areas must be completely black and
firmly drawn with sharp edges 2. The background must be smooth
white surface of high reflectance 3. Background materials need to
be opaque and reasonably stiff or dry-mounted
Slide 5
LINE ORIGINALS 5 Black and white line art images (graphics,
etc.) require little effort. The image represents binary data since
only black or white elements are present.
Slide 6
TONE ORIGINALS Embraces all pictures created in neutral tones
or grays of varying strength ranging from white to solid black
6
Slide 7
COLOR ORIGINALS To reproduce the colored picture the printer
must transfer layers of ink onto the white paper which will control
exactly the same amount of colored light as the original did 7
Slide 8
HALFTONE PROCESS 8 In printing, a technique of breaking up an
image into a series of dots so as to reproduce the full tone range
of a photograph or tone art work. The eye has limited resolving
power and, at a distance, is tricked into seeing these dots as
continuous tone.
Slide 9
HALFTONE PROCESS 9 Breaking up is usually done by a screen
inserted over the plate being exposed. The screens are made with a
varying number of lines per inch, depending on the application; for
newspapers, the range is 50 to 85, and for magazines, 100 to 120.
The highest quality reproduction requires 120 to 150 lines per
inch.
Slide 10
FILMS 10
Slide 11
FILMS 11 Panchromatic Film Orthochromatic Film Infra Red
Film
Slide 12
ORTHOCHROMATIC FILM 12 Orthochromatic film is sensitive to the
blue end of the spectrum, reaching the wavelength which produces
green light, but not red. Orthochromatic film makes warm colours
appear black and cool colours appear pale.
Slide 13
PANCHROMATIC FILM 13 Panchromatic film is a type of
black&white photographic film that is sensitive to all
wavelengths of visible light.black&whitephotographic
filmwavelengthsvisible light A panchromatic film produces a
realistic reproduction of a scene as it appears to the human eye.
Almost all modern films used are panchromatic As naturally
prepared, silver halide emulsions are much more sensitive to blue
and UV light than to green and red wavelengths.silver
halideemulsions
Slide 14
INFRA RED FILM 14 Infra red film is used in both scientific and
creative photography. It is a panchromatic film which has
sensitivity skewed to the red end of the spectrum
Slide 15
REQUIREMENTS ON FILMS 15 The types of film used particularly
for film image setters are subject to the following requirements:
they must be dimensionally stable, the exposed/dark areas must have
good opacity (optical density D=4), the unexposed/light areas must
be crystal clear (optical density D=0.05), they must have very
short exposure times, since the dots are imaged consecutively and
the total imaging time must remain acceptable, they must have sharp
edge definition, they must have high resolution
Slide 16
SENSITOMETRY 16 The scientific study of a photosensitive
material to different levels of exposures. How is it done?
Producing a sensitometric strip and plotting a characteristic
curve. A film containing number of areas with different optical
densities from white (fully transparent) to black (fully
opaque)
Slide 17
Why is the study important? 17 To produce images with optimum
contrast that reveal high details of the object examined. Optimum
contrast? Low contrast (long scale contrast) High contrast (Short
scale contrast)
Slide 18
Optimum contrast PHOTOGRAPHIC IMAGES High contrast Low
contrast
Slide 19
DENSITOMETRY 19 Densitometry is the quantitative measurement of
optical density in light-sensitive materials after exposure to
light.measurementoptical density The corresponding measuring device
is called a densitometer densitometer
Slide 20
TRANSMISSION DENSITOMETER 20 Transmission densitometers measure
transparent materials The densitometer is basically a light source
aimed at a photoelectric cell.photoelectric cell It determines the
density of a sample placed between the light source & the
photoelectric cell from differences in the readings.photoelectric
cell
Slide 21
NOW ITS YOUR TURN TO ANSWER 21 Types of originals? line, tone,
color Half tone screen angles for process colors? C 15deg, M 75deg,
Y 90deg, K 45deg Types of films? orthochromatic, panchromatic,
infrared Sensitometry? The scientific study of a photosensitive
material to different levels of exposures. Densitometer? measuring
device used to measure optical density in light sensitive
materials