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Digital Half Toning - Ordered Dithering - MATLAB Code Bayer/ Ulichney

Digital Half-toning is a technique to convert the gray scale / color image (in the range 0-255) to binary images (in the range 0-1)  that is useful for printing (especially black and white printers).




Though at first glance dots are clearly visible, as Human Vision System is a low pass filter, when dots are printed closely and viewed from the specific distance it can be perceived as a continuous tone image (i.e. gray scale). In general, half toning techniques is widely used in newspapers, journals and magazines printing. 

Halftoning algorithms aims for better

#Image Quality
#Low Complexity
#Optimal ink usage


Coming to the topic, Ordered dithering is one of the standard technique to produce halftone image from continuous (gray scale) images.




Let us assume, the first block containing 'B' is an image matrix and the  'H' is the threshold matrix.

And the process is simply a element wise (pixel wise) comparison;

if element of B > H (greater than) then print black ink, else print nothing. And depends on threshold matrix design it is categorized as clustered dot (green noise) and  dispersed dot (blue noise) dithering.

Bayer's ordered dithering is one of the conventional technique

Check this link for more info on Bayer's Dithering (MATLAB Code)

https://imageprocessing-sankarsrin.blogspot.com/2018/05/bayers-digital-halftoning-dispersed-and.html

Ulichney-digital-halftoning: (MATLAB Code)

https://imageprocessing-sankarsrin.blogspot.com/2018/06/ulichney-digital-halftoning-ordered.html


Here is the original and half toned image




Save the file:  imwrite(HOD, 'lenaOD.tif');   %if suppose HOD is the halftone image

For printing, open lenaOD.tif in photoshop, and Open Image--> Image Size--> Change resolution to 150 Pixels/Inch or whatsoever as per quality requirement( uncheck resampleimage). Print.

Cheers...!!



PYTHON CODE @ https://github.com/SankarSrin/Digital-Halftoning





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