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NB: I've rewritten this software in a much more portable and friendly form - see undither

I often want to edit or enlarge images I find in books for things like wallpaper or coffee mug &tc. However most images in books are heavily dithered and the usual methods for removing dithering suck badly.

Image takes a different approach to the problem, it calculates the image's power spectrum writes it out a colour ppm file. You load this into your favourite paint program and paint over in black any part of the spectrum you don't want it's usually very easy to see what parts are caused by dithering see the example below.


This first image is part of large japaense drawing.


Here's the image's power spectrum and we can see the bright spots associated with the dithering.


We load the image into our favourite paint program and draw over the bright spots and lines


Applying this filter gives us an almost perfect reconstruction of the image.


image chops images into 1024x1024 blocks and operates on each block and then recombines the image. [It calculates the power spectrum of the enter image though so you only need to paint over once]

Take me to the files