Generates a smoothness ordering of a RGB array to a linear gradient scale

smoothness.hexadecimal.sorting.js

function smooth(r, g, b, repetitions){
	/* 	Returns a smootheness HSV translation to a RGB value
		@author: Guilherme Branco Stracini (guilherme[at]editorainovacoa[dot]com[dot]br)
		@date:	2017-10-24
		@version: 1.0
		@remarks: Based on Python implementation of https://www.alanzucconi.com/2015/09/30/colour-sorting/ (accessed on 2017-10-24)
		@returns: {Object} Returns a object containing the H, S and V keys for each item (Hue, Saturation and Value)
	*/
	var lum, hsv, h, v;
	
	lum = Math.sqrt(.241 * r + .691 * g + .068 * b);
	
	hsv = rgb2hsv(r, g, b);
	
	h = parseInt(hsv.H * repetitions);
	v = parseInt(hsv.V * repetitions);
	
	if (h % 2 == 1)
	{
		v = repetitions - v;
		lum = repetitions - lum;		
	}
	
	return {H: h, S: lum, V: v};
}

function rgb2hsv(r, g, b){
	/* 	Returns a degree value between 0ยบ and 360ยบ for the defined hue angle, 
		the saturation and the brightness varying between 0 and 1 as the min and max value available
		for a input R G B variables (representing Red, Green and Blue between 0 and 255)
		@author: Guilherme Branco Stracini (guilherme[at]editorainovacoa[dot]com[dot]br)
		@date:	2017-10-24
		@version: 1.0
		@remarks: Based on formula available at http://www.ufrgs.br/engcart/PDASR/formulario1.html (accessed on 2017-10-24)
		@returns {Object} Returns an object with H, S and V keys
	*/
	
	var max, min, h, c;
	
	r = r / 255; //Converts 0...255 to 0...1
	g = g / 255; //Converts 0...255 to 0...1
	b = b / 255; //Converts 0...255 to 0...1
	
	max = Math.max(r, g, b);
	min = Math.min(r, g, b);
	    
	c = max - min;
    if(c == 0)
    	c = 1;
	
	if (max == r && g >= b)
		h = 60 * (g - b) / c;
	else if (max == r /*&& g < b*/)
		h = 60 * (g - b) / c + 360;
	else if (max == g)
		h = 60 * (b - r) / c + 120;
	else //if (max == b) 
		h = 60 * (r - g) / c + 240;
	
	return {H: h, S: c / max, V: max};
}	

function hex2RGB(hex){
	/* 	Converts a hexadecimal value to a RGB object that vary between 0 and 255
		the saturation and the brightness varying between 0 and 1 as the min and max value available
		for a input R G B variables (representing Red, Green and Blue between 0 and 255)
		@author: Guilherme Branco Stracini (guilherme[at]editorainovacoa[dot]com[dot]br)
		@date:	2017-10-24
		@version: 1.0
		@returns {Object} Returns an object with R, G and B keys
		@example
		//returns {R: 255, G: 255, B: 255}; 
		hex2RGB('#FFFFFF');
		@example
		//returns {R: 255, G: 51, B: 0};
		hex2RGB('#FF3300');
	*/
	var r = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
	if(!r)
		return null;
	return {R: parseInt(r[1], 16), G: parseInt(r[2], 16), B: parseInt(r[3], 16)};
}

function smoothHexSort(hexA, hexB){
	/*	Provides a sorting filter for a hexadecimal values, using a smoothness pattern
		@author: Guilherme Branco Stracini (guilherme[at]editorainovacoa[dot]com[dot]br)
		@date:	2017-10-24
		@version: 1.0
		@returns {Number} A value for filtering
	*/
	var rgbA = hex2RGB(hexA);
	var rgbB = hex2RGB(hexB);
	var sumA = rgbA.R + rgbA.G + rgbA.B;
	var sumB = rgbB.R + rgbB.G + rgbB.B;
	var hsvA = smooth(rgbA.R, rgbA.G, rgbA.B, 8);
	var hsvB = smooth(rgbB.R, rgbB.G, rgbB.B, 8);
    	var a = hsvA.H + hsvA.S + hsvA.V;
	var b = hsvB.H + hsvB.S + hsvB.V;
	return a - b;
}