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color_conversions.c
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color_conversions.c
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// http://www.easyrgb.com/index.php?X=MATH&H=02#text2
#include <stdio.h>
#include <math.h>
float ref_X = 95.047;
float ref_Y = 100.0;
float ref_Z = 108.883;
/***************************************************
* Name: convertRGBtoXYZ
*
* Returns: Nothing
*
* Parameters: RGB values and XYZ references
*
* Description: Given a color in RGB values converts
* to the corresponding XYZ values
*
***************************************************/
void convertRGBtoXYZ(int inR, int inG, int inB, float * outX, float * outY, float * outZ) {
float var_R = (inR / 255.0f); //R from 0 to 255
float var_G = (inG / 255.0f); //G from 0 to 255
float var_B = (inB / 255.0f); //B from 0 to 255
if (var_R > 0.04045f)
var_R = powf(( (var_R + 0.055f) / 1.055f), 2.4f);
else
var_R = var_R / 12.92f;
if (var_G > 0.04045)
var_G = powf(( (var_G + 0.055f) / 1.055f), 2.4f);
else
var_G = var_G / 12.92f;
if (var_B > 0.04045f)
var_B = powf(( (var_B + 0.055f) / 1.055f), 2.4f);
else
var_B = var_B / 12.92f;
var_R = var_R * 100;
var_G = var_G * 100;
var_B = var_B * 100;
//Observer. = 2°, Illuminant = D65
*outX = var_R * 0.4124f + var_G * 0.3576f + var_B * 0.1805f;
*outY = var_R * 0.2126f + var_G * 0.7152f + var_B * 0.0722f;
*outZ = var_R * 0.0193f + var_G * 0.1192f + var_B * 0.9505f;
}
/***************************************************
* Name: convertXYZtoLab
*
* Returns: Nothing
*
* Parameters: XYZ values and Lab references
*
* Description: Given a color in XYZ values converts
* to the corresponding Lab values
*
***************************************************/
void convertXYZtoLab(float inX, float inY, float inZ, float * outL, float * outa, float * outb) {
float var_X = (inX / ref_X); //ref_X = 95.047
float var_Y = (inY / ref_Y); //ref_Y = 100.0
float var_Z = (inZ / ref_Z); //ref_Z = 108.883
if ( var_X > 0.008856 )
var_X = powf(var_X , ( 1.0f/3 ));
else
var_X = ( 7.787 * var_X ) + ( 16.0f/116 );
if ( var_Y > 0.008856 )
var_Y = powf(var_Y , ( 1.0f/3 ));
else
var_Y = ( 7.787 * var_Y ) + ( 16.0f/116 );
if ( var_Z > 0.008856 )
var_Z = powf(var_Z , ( 1.0f/3 ));
else
var_Z = ( 7.787 * var_Z ) + ( 16.0f/116 );
*outL = ( 116 * var_Y ) - 16;
*outa = 500 * ( var_X - var_Y );
*outb = 200 * ( var_Y - var_Z );
}
/***************************************************
* Name: convertLabtoXYZ
*
* Returns: Nothing
*
* Parameters: Lab values and XYZ references
*
* Description: Given a color in Lab values converts
* to the corresponding XYZ values
*
***************************************************/
void convertLabtoXYZ( float inL, float ina, float inb, float * outX, float * outY, float * outZ) {
float var_Y = ( inL + 16 ) / 116;
float var_X = (ina/500) + var_Y;
float var_Z = var_Y - (inb/200);
if ( powf(var_Y,3.f) > 0.008856 )
var_Y = powf(var_Y,3.f);
else
var_Y = ( var_Y - (16/116) ) / 7.787;
if ( powf(var_X,3.f) > 0.008856 )
var_X = powf(var_X,3.f);
else
var_X = ( var_X - (16/116) ) / 7.787;
if ( powf(var_Z,3.f) > 0.008856 )
var_Z = powf(var_Z,3.f);
else
var_Z = ( var_Z - (16/116) ) / 7.787;
*outX = ref_X * var_X; //ref_X = 95.047 Observer= 2°, Illuminant= D65
*outY = ref_Y * var_Y; //ref_Y = 100.000
*outZ = ref_Z * var_Z; //ref_Z = 108.883
}
/***************************************************
* Name: convertXYZtoRGB
*
* Returns: Nothing
*
* Parameters: XYZ values and RGB references
*
* Description: Given a color in XYZ values converts
* to the corresponding RGB values
*
***************************************************/
void convertXYZtoRGB(float inX, float inY, float inZ, int * outR, int * outG, int * outB) {
float var_X = inX/100;
float var_Y = inY/100;
float var_Z = inZ/100;
float var_R = var_X * 3.2406 + (var_Y * -1.5372) + var_Z * (-0.4986);
float var_G = var_X * (-0.9689) + var_Y * 1.8758 + var_Z * 0.0415;
float var_B = var_X * 0.0557 + var_Y * (-0.2040) + var_Z * 1.0570;
if ( var_R > 0.0031308 )
var_R = 1.055 * powf(var_R, ( 1.0f / 2.4 ) ) - 0.055;
else
var_R = 12.92 * var_R;
if ( var_G > 0.0031308 )
var_G = 1.055 * powf(var_G, ( 1.0f / 2.4 ) ) - 0.055;
else
var_G = 12.92 * var_G;
if ( var_B > 0.0031308 )
var_B = 1.055 * powf(var_B, ( 1.0f / 2.4 ) ) - 0.055;
else
var_B = 12.92 * var_B;
*outR = (int)(var_R * 255);
*outG = (int)(var_G * 255);
*outB = (int)(var_B * 255);
}
/***************************************************
* Name: Lab_color_difference_CIE76
*
* Returns: float
*
* Parameters: 2 Lab color values
*
* Description: Calculates and returns the difference
* between 2 Lab colors based on the CIE76 formula
*
***************************************************/
float Lab_color_difference_CIE76( float inL1, float ina1, float inb1, float inL2, float ina2, float inb2){
return( sqrt( powf(inL1 - inL2, 2.f) + powf(ina1 - ina2, 2.f) + powf(inb1 - inb2, 2.f) ) );//CIE76
}
/***************************************************
* Name: RGB_color_Lab_difference_CIE76
*
* Returns: float
*
* Parameters: 2 RGB color values
*
* Description: Converts RGB values to Lab values and returns
* the difference between 2 Lab colors based on
* the CIE76 formula
*
***************************************************/
float RGB_color_Lab_difference_CIE76( int R1, int G1, int B1, int R2, int G2, int B2){
float x1=0,y1=0,z1=0;
float x2=0,y2=0,z2=0;
float l1=0,a1=0,b1=0;
float l2=0,a2=0,b2=0;
convertRGBtoXYZ(R1, G1, B1, &x1, &y1, &z1);
convertRGBtoXYZ(R2, G2, B2, &x2, &y2, &z2);
convertXYZtoLab(x1, y1, z1, &l1, &a1, &b1);
convertXYZtoLab(x2, y2, z2, &l2, &a2, &b2);
return( Lab_color_difference_CIE76(l1 ,a1 ,b1 ,l2 ,a2 ,b2) );
}
/***************************************************
* Name: Lab_color_difference_CIE94
*
* Returns: float
*
* Parameters: 2 Lab color values
*
* Description: Calculates and returns the difference
* between 2 Lab colors based on the CIE94 formula
*
***************************************************/
float Lab_color_difference_CIE94( float inL1, float ina1, float inb1, float inL2, float ina2, float inb2){
// case Application.GraphicArts:
float Kl = 1.0;
float K1 = 0.045;
float K2 = 0.015;
// break;
// case Application.Textiles:
// Kl = 2.0;
// K1 = .048;
// K2 = .014;
// break;
float deltaL = inL1 - inL2;
float deltaA = ina1 - ina2;
float deltaB = inb1 - inb2;
float c1 = sqrt(pow(ina1, 2) + pow(inb1, 2));
float c2 = sqrt(pow(ina2, 2) + pow(inb2, 2));
float deltaC = c1 - c2;
float deltaH = pow(deltaA,2) + pow(deltaB,2) - pow(deltaC,2);
deltaH = deltaH < 0 ? 0 : sqrt(deltaH);
const float sl = 1.f;
const float kc = 1.f;
const float kh = 1.f;
float sc = 1.f + K1*c1;
float sh = 1.f + K2*c1;
float i = pow(deltaL/(Kl*sl), 2) +
pow(deltaC/(kc*sc), 2) +
pow(deltaH/(kh*sh), 2);
float finalResult = i < 0 ? 0 : sqrt(i);
return (finalResult);
}
/***************************************************
* Name: RGB_color_Lab_difference_CIE94
*
* Returns: float
*
* Parameters: 2 RGB color values
*
* Description: Converts RGB values to Lab values and returns
* the difference between 2 Lab colors based on
* the CIE94 formula
*
***************************************************/
float RGB_color_Lab_difference_CIE94( int R1, int G1, int B1, int R2, int G2, int B2){
float x1=0,y1=0,z1=0;
float x2=0,y2=0,z2=0;
float l1=0,a1=0,b1=0;
float l2=0,a2=0,b2=0;
convertRGBtoXYZ(R1, G1, B1, &x1, &y1, &z1);
convertRGBtoXYZ(R2, G2, B2, &x2, &y2, &z2);
convertXYZtoLab(x1, y1, z1, &l1, &a1, &b1);
convertXYZtoLab(x2, y2, z2, &l2, &a2, &b2);
return( Lab_color_difference_CIE94(l1 ,a1 ,b1 ,l2 ,a2 ,b2) );
}
/***************************************************
* Name: main
*
* Returns: Nothing
*
* Parameters: argc, **argv
*
* Description: Running some tests
*
***************************************************/
void main(int argc, char const *argv[])
{
int R1,G1,B1,R2,G2,B2;
float x=0.f,y=0.f,z=0.f;
float l=0.f,a=0.f,b=0.f;
R1 = 200;
G1 = 2;
B1 = 50;
R2 = 200;
G2 = 2;
B2 = 70;
printf("LAB DISTANCE = %lf \n", RGB_color_Lab_difference_CIE94(R1,G1,B1,R2,G2,B2) );
}