# Comparing Colors using Delta-E in C#

I’ve had to do some work on color comparison recently. There are some really great algorithms out there for this, particularly at easyrgb.com. Unfortunately, I couldn’t find a good C# version of this anywhere, so I had to convert my own. So for my own future reference, and for anyone that needs it here it is.

``````public class ColorFormulas
{
public double X { get; set; }
public double Y { get; set; }
public double Z { get; set; }

public double CieL { get; set; }
public double CieA { get; set; }
public double CieB { get; set; }

public ColorFormulas(int R, int G, int B)
{
RGBtoLAB(R, G, B);
}

public void RGBtoLAB(int R, int G, int B)
{
RGBtoXYZ(R, G, B);
XYZtoLAB();
}

public void RGBtoXYZ(int RVal, int GVal, int BVal)
{
double R = Convert.ToDouble(RVal) / 255.0;       //R from 0 to 255
double G = Convert.ToDouble(GVal) / 255.0;       //G from 0 to 255
double B = Convert.ToDouble(BVal) / 255.0;       //B from 0 to 255

if (R > 0.04045)
{
R = Math.Pow(((R + 0.055) / 1.055), 2.4);
}
else
{
R = R / 12.92;
}
if (G > 0.04045)
{
G = Math.Pow(((G + 0.055) / 1.055), 2.4);
}
else
{
G = G / 12.92;
}
if (B > 0.04045)
{
B = Math.Pow(((B + 0.055) / 1.055), 2.4);
}
else
{
B = B / 12.92;
}

R = R * 100;
G = G * 100;
B = B * 100;

//Observer. = 2°, Illuminant = D65
X = R * 0.4124 + G * 0.3576 + B * 0.1805;
Y = R * 0.2126 + G * 0.7152 + B * 0.0722;
Z = R * 0.0193 + G * 0.1192 + B * 0.9505;
}

public void XYZtoLAB()
{
// based upon the XYZ - CIE-L*ab formula at easyrgb.com (http://www.easyrgb.com/index.php?X=MATH&H=07#text7)
double ref_X = 95.047;
double ref_Y = 100.000;
double ref_Z = 108.883;

double var_X = X / ref_X;         // Observer= 2°, Illuminant= D65
double var_Y = Y / ref_Y;
double var_Z = Z / ref_Z;

if (var_X > 0.008856)
{
var_X = Math.Pow(var_X , (1 / 3.0));
}
else
{
var_X = (7.787 * var_X) + (16 / 116.0);
}
if (var_Y > 0.008856)
{
var_Y = Math.Pow(var_Y, (1 / 3.0));
}
else
{
var_Y = (7.787 * var_Y) + (16 / 116.0);
}
if (var_Z > 0.008856)
{
var_Z = Math.Pow(var_Z, (1 / 3.0));
}
else
{
var_Z = (7.787 * var_Z) + (16 / 116.0);
}

CieL = (116 * var_Y) - 16;
CieA = 500 * (var_X - var_Y);
CieB = 200 * (var_Y - var_Z);
}

///
/// The smaller the number returned by this, the closer the colors are
///
///
///
public int CompareTo(ColorFormulas oComparisionColor)
{
// Based upon the Delta-E (1976) formula at easyrgb.com (http://www.easyrgb.com/index.php?X=DELT&H=03#text3)
double DeltaE = Math.Sqrt(Math.Pow((CieL - oComparisionColor.CieL), 2) + Math.Pow((CieA - oComparisionColor.CieA), 2) + Math.Pow((CieB - oComparisionColor.CieB), 2));
return Convert.ToInt16(Math.Round(DeltaE));
}

public static int DoFullCompare(int R1, int G1, int B1, int R2, int G2, int B2)
{
ColorFormulas oColor1 = new ColorFormulas(R1, G1, B1);
ColorFormulas oColor2 = new ColorFormulas(R2, G2, B2);
return oColor1.CompareTo(oColor2);
}
}``````