[Gimp-print-devel] Article: adaptive methods for dithering color images

[Hrafnkell E. <he...@kv...>]

Hi

I would like to point you to an interesting article on using
a Least Mean Square algorithm to choose the coefficients for
the error diffusion filter kernel:

Lale Akarun, Yasemin Yardimci and A. Enis Cetin:
"Adaptive Methods for Dithering Color Images"
IEEE Transactions on Image Processing, vol 6, no 7, july 1997.

Quotes form the conclusion:
"The appearance of color impulses is greatly eliminated and smoother
 color transitions are achived"

and

"Both of the adaptive error diffusion algorithms show a distinct improvement
 in performance when compared with the Floyd-Steinberg filter"

Given that I have some time available after my exams this summer I 
would like to try to implement the algorithm.

One thing that some might like to try out from the article:

"The scaling of the error diffusion filter coefficients is an important
 step in the performance of the algorithm. This scaling coefficient 
 controls the balance of false edges and color impulses; it can,
 therefore be varied in different regions of an image to
 achive different goals."

The main point with that is that the coefficient of the Floyd Steinberg
(and other) filter kernels sum up to one. By making the sum up to f.x.
0.9 the effects of quantization error accumulation that leads to a
disturbing color impulse in pale areas can be reduced.
A first thing to try might be to use some heuristics to change a scale
factor. I have a feeling that rlk has developed some heuristics he uses,
at least in his head when playing with the dithering algorithms, that
might be used.

Just a thought...

Homework here I come!
-- 
//-----------------------//-------------------------------------------------
//  Hrafnkell Eiriksson  // 
//  he...@kv...        // 
//  TF3HR                //  "Blessed are they who go around in circles,
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