unit RGBCIEUtils;

interface

uses
  SysUtils,
  {$IFDEF FPC}LCLIntf,{$ELSE}Windows,{$ENDIF}
  Graphics, Math;

const
 {// Observer= 2°, Illuminant= D65    - Daylignt
 ref_X =  95.047;
 ref_Z = 108.883;
 // Observer= 10°, Illuminant= D65   - Daylight
 ref_X =  94.811;
 ref_Z = 35.2;

 // Observer= 2°, Illuminant= A      - Incadescent
 ref_X =  109.850;
 ref_Z = 35.585;
 // Observer= 10°, Illuminant= A     - Incadescent
 ref_X =  111.144;
 ref_Z = 35.2;

 // Observer= 2°, Illuminant= C
 ref_X =  98.074;
 ref_Z = 118.232;
 // Observer= 10°, Illuminant= C
 ref_X =  97.285;
 ref_Z = 116.145;
                }
 // Observer= 2°, Illuminant= D50
 ref_X =  96.422;
 ref_Z = 82.521;{
 // Observer= 10°, Illuminant= D50 - Photoshop
 ref_X =  96.72;
 ref_Z = 81.427; }

 {// Observer= 2°, Illuminant= D55
 ref_X =  95.682;
 ref_Z = 92.149;
 // Observer= 10°, Illuminant= D55
 ref_X =  95.799;
 ref_Z = 90.926;

 // Observer= 2°, Illuminant= D75
 ref_X =  94.972;
 ref_Z = 122.638;
 // Observer= 10°, Illuminant= D75
 ref_X =  94.416;
 ref_Z = 12.641;

 // Observer= 2°, Illuminant= F2     - Fluorescent
 ref_X =  99.187;
 ref_Z = 67.395;
 // Observer= 10°, Illuminant= F2    - Fluorescent
 ref_X =  103.28;
 ref_Z = 69.026;

 // Observer= 2°, Illuminant= F7
 ref_X =  95.044;
 ref_Z = 108.755;
 // Observer= 10°, Illuminant= F7
 ref_X =  95.792;
 ref_Z = 107.678;

 // Observer= 2°, Illuminant= F11
 ref_X =  100.966;
 ref_Z = 64.370;
 // Observer= 10°, Illuminant= F11
 ref_X =  103.866;
 ref_Z = 65.627;   }

type
 xyz = record
  x: real;
  y: real;
  z: real;
 end;

function LabToXYZ(l, a, b: real): xyz;
function XYZToRGB(space: xyz): TColor;
function LabToRGB(l, a, b: real): TColor;
function RGBToXYZ(c: TColor): xyz;
procedure RGBToLab(clr: TColor; var l, a, b: real);
procedure XYZToLab(space: xyz; var l, a, b: real);
procedure LCHToLab(lum, c, h: real; var l, a, b: real);
procedure LabToLCH(l, a, b: real; var lum, c, h: real);
function LCHToRGB(l, c, h: real): TColor;
procedure RGBToLCH(clr: TColor; var l, c, h: real);
function GetCIEXValue(c: TColor): real;
function GetCIEYValue(c: TColor): real;
function GetCIEZValue(c: TColor): real;
function GetCIELValue(c: TColor): real;
function GetCIEAValue(c: TColor): real;
function GetCIEBValue(c: TColor): real;
function GetCIECValue(c: TColor): real;
function GetCIEHValue(c: TColor): real;

implementation

function LabToXYZ(l, a, b: real): xyz;
var
 x, y, z: real;
begin
 y := (l + 16)/116;
 x := a/500 + y;
 z := y - b/200;
 if y > 0.2069 then
  y := IntPower(y, 3)
 else
  y := (y - 0.138)/7.787;
 if x > 0.2069 then
  x := IntPower(x, 3)
 else
  x := (x - 0.138)/7.787;
 if z > 0.2069 then
  z := IntPower(z, 3)
 else
  z := (z - 0.138)/7.787;
 Result.x := ref_X * x;
 Result.y := 100 * y;
 Result.z := ref_Z * z;
end;

function XYZToRGB(space: xyz): TColor;
var
 r, g, b, x, y, z: real;
begin
 x := space.x/100;
 y := space.y/100;
 z := space.z/100;
 r := x * 3.2406 + y * (-1.5372) + z * (-0.49);
 g := x * (-0.969) + y * 1.8758 + z * 0.0415;
 b := x * 0.0557 + y * (-0.2040) + z * 1.0570;
 if r > 0.00313 then
  r := 1.055 * Power(r, 1/2.4) - 0.055
 else
  r := 12.92 * r;
 if g > 0.00313 then
  g := 1.055 * Power(g, 1/2.4) - 0.055
 else
  g := 12.92 * g;
 if b > 0.00313 then
  b := 1.055 * Power(b, 1/2.4) - 0.055
 else
  b := 12.92 * b;

 if r < 0 then r := 0;
 if r > 1 then r := 1;
 if g < 0 then g := 0;
 if g > 1 then g := 1;
 if b < 0 then b := 0;
 if b > 1 then b := 1;
 Result := RGB(Round(r*255), Round(g*255), Round(b*255));
end;

function LabToRGB(l, a, b: real): TColor;
begin
 Result := XYZToRGB(LabToXYZ(l, a, b));
end;

function RGBToXYZ(c: TColor): xyz;
var
 r, g, b: real;
begin
 r := GetRValue(c)/255;
 g := GetGValue(c)/255;
 b := GetBValue(c)/255;
 if r > 0.04045 then
  r := Power((r + 0.055)/1.055, 2.4)
 else
  r := r/12.92;
 if g > 0.04045 then
  g := Power((g + 0.055)/1.055, 2.4)
 else
  g := g/12.92;
 if b > 0.04045 then
  b := Power((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
 Result.x := r * 0.4124 + g * 0.3576 + b * 0.1805;
 Result.y := r * 0.2126 + g * 0.7152 + b * 0.0722;
 Result.z := r * 0.0193 + g * 0.1192 + b * 0.9505;
end;

procedure XYZToLab(space: xyz; var l, a, b: real);
var
x, y, z: real;
begin
 x := space.x/ref_X;
 y := space.y/100;
 z := space.z/ref_Z;
 if x > 0.008856 then
  x := Power(x, 1/3)
 else
  x := (7.787*x) + 0.138;
 if y > 0.008856 then
  y := Power(y, 1/3)
 else
  y := (7.787*y) + 0.138;
 if z > 0.008856 then
  z := Power(z, 1/3)
 else
  z := (7.787*z) + 0.138;
 l := (116*y) - 16;
 a := 500 * (x - y);
 b := 200 * (y - z);
 if l > 100 then l := 100;
 if l < 0 then l := 0;
 if a < -128 then a := -128;
 if a > 127 then a := 127;
 if b < -128 then b := -128;
 if b > 127 then b := 127;
end;

procedure RGBToLab(clr: TColor; var l, a, b: real);
var
 s: xyz;
begin
 s := RGBToXYZ(clr);
 XYZToLab(s, l, a, b);
end;

procedure LCHToLab(lum, c, h: real; var l, a, b: real);
begin
 l := lum;
 a := cos(DegToRad(h)) * c;
 b := sin(DegToRad(h)) * c;
end;

procedure LabToLCH(l, a, b: real; var lum, c, h: real);
begin
 h := ArcTan2(b, a);
 if h > 0 then
  h := (h/PI) * 180
 else
  h := 360 - (ABS(h)/PI) * 180;
 lum := l;
 c := SQRT(a*a + b*b);
end;

procedure RGBToLCH(clr: TColor; var l, c, h: real);
var
 a, b: real;
begin
 RGBToLab(clr, l, a, b);
 LabToLCH(l, a, b, l, c, h);
end;

function LCHToRGB(l, c, h: real): TColor;
var
 lum, a, b: real;
begin
 LCHToLab(l, c, h, lum, a, b);
 Result := LabToRGB(lum, a, b);
end;

function GetCIEXValue(c: TColor): real;
var
 d: xyz;
begin
 d := RGBToXYZ(c);
 Result := d.x;
end;

function GetCIEYValue(c: TColor): real;
var
 d: xyz;
begin
 d := RGBToXYZ(c);
 Result := d.y;
end;

function GetCIEZValue(c: TColor): real;
var
 d: xyz;
begin
 d := RGBToXYZ(c);
 Result := d.z;
end;

function GetCIELValue(c: TColor): real;
var
 d: real;
begin
 XYZToLab(RGBToXYZ(c), Result, d, d);
end;

function GetCIEAValue(c: TColor): real;
var
 d: real;
begin
 XYZToLab(RGBToXYZ(c), d, Result, d);
end;

function GetCIEBValue(c: TColor): real;
var
 d: real;
begin
 XYZToLab(RGBToXYZ(c), d, d, Result);
end;

function GetCIECValue(c: TColor): real;
var
 d: real;
begin
 RGBToLCH(c, d, Result, d);
end;

function GetCIEHValue(c: TColor): real;
var
 d: real;
begin
 RGBToLCH(c, d, d, Result);
end;

end.