Mumbai University > Computer Engineering > Sem 4 > Computer Graphics

Marks: 5 Marks

Year: May 2016

Dithering technique:

1. Another technique for digital half toning is dithering.
2. It is the technique for approximating halftones without reducing resolution, as pixel grid patterns do.
3. Dithering can be accomplished by Thresholding the image against a dither matrix.
4. To obtain $n^2$ intensity levels, it is necessary to setup an n x n dither matrix $D_n$ whose elements are distinct positive integers in the range of 0 to $n^2$ – 1.

5. Matrix for 4 intensity level and 9 intensity level is shown below.

   

6. The elements of a dither matrix are thresholds.
7. The matrix is laid like a tile over the entire image and each pixel value is compared with the corresponding threshold from the matrix
8. The pixel becomes white if its value exceeds the threshold or black otherwise.
9. This approach produces an output image with the same dimensions as the input image, but with less detail visible.
10. High order dither matrices can be obtained from lower order matrices with the recurrence relation

Algorithm to halftone an image using a dither matrix: