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Digital Image Processing
Some Special Techniques
Some Special Techniques
Dithering
Dithering
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21/11/15 Duong Anh Duc - Digital Image Processing
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Dithering
Dithering
Dithering, also called Halftoning or Color
Dithering, also called Halftoning or Color
Reduction, is the process of rendering an
Reduction, is the process of rendering an
image on a display device with fewer colors
image on a display device with fewer colors
than are in the image. (
than are in the image. (Mateus Pins and
Mateus Pins and
Hermann Hild
Hermann Hild)
)
The number of different colors in an image or
The number of different colors in an image or
on a device is used called its Color Resolution.
on a device is used called its Color Resolution.
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Dithering
Dithering
If the display device has a higher spatial resolution
If the display device has a higher spatial resolution
than the image that you are trying to reproduce, it can
than the image that you are trying to reproduce, it can
show a very good image even if its color resolution is
show a very good image even if its color resolution is
less. This is what we will call 'dithering' and is the
less. This is what we will call 'dithering' and is the
subject of this work.
subject of this work.
Dithering is a one-way operation.
Dithering is a one-way operation.
Once an image has been dithered, although it may look like
Once an image has been dithered, although it may look like
a good reproduction of the original, information is
a good reproduction of the original, information is
permanently lost.
permanently lost.
Many image processing functions fail on dithered images.
Many image processing functions fail on dithered images.
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Dithering
Dithering
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Dithering
Dithering
Grey-scale and colour simulation
Grey-scale and colour simulation
Dithering on a screen or printer is analogous to
Dithering on a screen or printer is analogous to
the half-toning techniques used in the print
the half-toning techniques used in the print
industry.
industry.
A CRT can be considered to be a complex
A CRT can be considered to be a complex
colour “dithering” device with variable colour
colour “dithering” device with variable colour
intensity.
intensity.
