"Dithering, also called Halftoning or Color Reduction,

is the process of rendering an image

on a display device

with fewer colors than are in the image."

                                                                                (Mateus Pins and Hermann Hild)

 

What is Dithering?

 

Dithering, also called Halftoning or Color Reduction, is the process of rendering an image on a display device with fewer colors than are in the image. The number of different colors in an image or on a device is used called its Color Resolution. The term 'resolution' means 'fineness' and is used to describe the level of detail in a digitally sampled signal. It is used most often in referring to the Spatial Resolution, which is the basic sampling rate for a digitized image.

If the display device has a higher spatial resolution than the image that you are trying to reproduce, it can show a very good image even if its color resolution is less. This is what we will call 'dithering' and is the subject of this work.

It is important to emphasize here that dithering is a one-way operation. Once an image has been dithered, although it may look like a good reproduction of the original, information is permanently lost. Many image processing functions fail on dithered images. For these reasons, dithering must be considered only as a way to produce an image on hardware at would otherwise be incapable of displaying it. The data representing an image should always be kept in full detail.

The aim of this project is to study and to develop the methods of dithering that are described in the papers 'Halftoning with Image-Based Dither Screens', 'Texture-based Dither Matrices' and 'Artistic Screening with Arbitrary Textures' by Oleg Veryovka and John Buchanan. As a consequence of this work our team developed a simple variation of these 'Veryovka-Buchanan' dithering methods that we had learnt. This 'new method' of dithering was called APW dithering. This method is based on segmentation using global threshold.

Here we also describe some classic algorithms of Dithering (e.g. average dithering, Floyd-Steinberg dithering, ordered dithering and random dithering) that we implemented for our learning and technical comparison.

The result of this work is a simple software called 'Image Based Artistic Dithering' that implements all these methods aforementioned.

Revised: 12.13.2000 .