1. ## About Dithering & Halftoning

Hello all this is my first post to the forum, i am student Computer Science, recently I am working on Visual Cryptography, and i need a few image processing help there, the thing is I am completely n00b with DIP,

My goal is to convert a color image to it's binary equivalent, I mean I want to convert an image such that only 3 colors should be there Cyan, Magenta, Yellow so a pixel can be represented by these 3 colors only, like black can be represented as (1,1,1) white (0,0,0), blue (1,1,0) [order :- (C,M,Y)]

How can I do it? by dithering or halftoning?

and can anyone provide me any software or C code for the above?

2. ## Re: About Dithering & Halftoning

My suggestion would be to use the wiki - http://en.wikipedia.org/wiki/Dither - will give you an idea about some different dithering techniques if you follow the links, etc. Once you've sorted that out, then you can manually generate an image in the uncompressed 'tga' format - http://en.wikipedia.org/wiki/Truevision_TGA - gives some pointers wrt the format. Make that image small, say, 10 by 10 pixels. Then use a spread sheet to apply your preferred dithering algorithm. Once you are getting to where you want to be, then use a larger 'real world' digital image, to see how that works out. There is plenty of software to convert bmp's/ jpeg's/tif's/whatever to tga's, and that is the easiest image format to work with.

As you are a student of computer science, it should be trivial for you to write your own software to do what you want, if you need answers faster than the spread sheet can produce when handling larger files. something like notepad++ will let you examine the layout/content of image and most other files.

hth

3. ## Re: About Dithering & Halftoning

One thing you should be aware of, is because of relatively low ink density, CMY won't generate good blacks, and precisely why the prepress industry uses CMYk as they need the k ink to get good blacks.

However if it is only theory you are after, then the C, M and Y pigments or filters can be 'perfectly pure' secondaries and you are fine.