Halftone
Dosed by Arun Daniel – M & E Team (From MphasiS Software Services)
What is Halftone?
Halftone is an image converted into small dots to fool your eye into seeing
shades of gray (or tints of a color). Depending on the tones present in the
image, the dots may vary in size. The dots start out very small in light areas,
and grow in size as the shade gets darker. Eventually, the dots overlap,
revealing only small amounts of the background. Usually, even the large dots
are so small your eye can’t distinguish them as individual dots, and they blur
together into shades of gray.
Picture1: The picture on the left is turned into a halftone
Halftone exists because it is not possible to print continuous tones on a
printing press; in other words it cannot print shades of gray. There is only
ink or no ink; so you cannot vary the amount of ink at any given point. That’s
fine if you’re printing only text; black type, white paper but when you want to
print photographic images, which are nothing but continuous tones, things can
get bit trickier, however.
Take a simple black rectangle, as shown below.
Picture2
A basic filled shape, such as a black rectangle, is easy to print.
There is no variation of color throughout it, so it can be printed as one solid
image.
However, something like the picture above (Picture1) is bit more complicated.
So a method was developed to simulate the changes in tone using only black ink
for black and white photos. For a photo to be printed on a printing press it
must first be converted into a “halftone”. A halftone is an image whose
continuous tones have been converted to a pattern of solid dots. When viewed as
a whole, this pattern of dots appears as continuous tone, when actually, it is
not.
What is its usefulness?
Halftone images use used in newspapers and magazines because it is a much more
efficient way to print images. Since a halftone image is made up of discreet
dots, it requires significantly less ink to print than a continuous tone image.
As long as the resolution of the image is high enough, the dots appear as a
continuous image to the human eye. However, if you closely examine the images
printed in a newspaper, you should be able to see the dots that make up the
halftone image.
Further References
http://desktoppub.about.com/cs/halftones/a/halftones.htm
http://www.pstut.com/tutorial-image-halftone-effect.html
http://www.u-cwebs.com/usability/web-site-usability.htm
http://psdtuts.com/tutorials-effects/create-a-cool-halftone-effect/
http://www.viruslist.com/en/glossary?glossid=189210535
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