Markus13

@toe_head2001, thanks for pointing out older sources of PaintNET. After digging it i found that the actual algorithm of posterization uses some kind of pre-generated palette. So the whole process done in two steps: first there should be formed palettes for each level (Red, Green, Blue), depending on input values of the filter: redLevels = CalcLevels( posterizeValRed ); greenLevels = CalcLevels( posterizeValGreen ); blueLevels = CalcLevels( posterizeValBlue ); function CalcLevels( inputVal ){ // inputVal is int[2..64] var t1 = new Array( inputVal ); // array of byte var i; // byte for (i = 0; i < inputVal; i++){ t1[i] = IntToByte( Round( (255 * i) / (inputVal - 1) ) ); } var levels = new Array( 256 ); // array of byte var j = 0; // byte var k = 0; // int16 for(i = 0; i <= 255; i++){ levels[i] = t1[j]; k += inputVal; if( k > 255 ){ k -= 255; j++; } } return levels; } and in the second step we should perform next operation on each pixel of image: function PixelOperation( srcColor ){ var byteRed = getRvalue( srcColor ); // byte var byteGreen = getGvalue( srcColor ); // byte var byteBlue = getBvalue( srcColor ); // byte var byteAlpha = getAvalue( srcColor ); // byte byteRed = redLevels[byteRed]; byteGreen = greenLevels[byteGreen]; byteBlue = blueLevels[byteBlue]; //byteAlpha = alphaLevels[byteAlpha]; // we can do the same for alpha if we need to return RGBA( byteRed, byteGreen, byteBlue, byteAlpha ); } By the way, if we will implement this algorithm in some compiling language (i used JavaScript just to demonstrate the approach) - it will be much faster than standard approach, cuz with this method there will be only 3 (4 with alpha) writing instructions for each pixel. So the overall posterization-application time will be like 2-3 times faster (or even more, depending on image-size) comparing to standard posterization algorithm, which has floating-point calculations for each color-byte of each pixel.

Well, after some additional tests today it's clear that it's not a matter of input values - seems that posterization in PaintNET also tweaks saturation/contrast/brightness in some way. So it's obviously a different algorithm. And i'll appreciate if somebody will provide information about it.

I'm working on automatic graphics processing utility which performs batch-actions on a bunch of image-files, and i wonder how input values from Posterize-effect in PaintNET could be used. So i have a standard posterization algorithm in my program: byteRed = IntToByte( Round( byteRed / posterizeValRed ) * posterizeValRed ); byteGreen= IntToByte( Round( byteGreen / posterizeValGreen ) * posterizeValGreen ); byteBlue = IntToByte( Round( byteBlue / posterizeValBlue ) * posterizeValBlue ); byteAlpha = IntToByte( Round( byteAlpha / posterizeValAlpha ) * posterizeValAlpha ); But input values for posterization effect (a number from 2 to 64) in PaintNET are very confusing. So the question is - how can i interpret them to use in my utility? EDIT: or maybe somebody knows the algorithm which used in PaintNET so i can change my implementation of it accordingly... P.S. Not sure if i made post in appropriate section of this forum. I'm sorry if not.