标签:
Why an article on "colors"? It‘s the same question I asked myself before writing this series.
The fact is, in .NET, there are only two color formats that can be used: the RGB color model and the HSB color model. Those two are encapsulated in the Color
structure of the System.Drawing
namespace.
It is largely sufficient for simple uses, like changing the background color of a component, but insufficient if we want to develop graphic tools (or something which implies conversion between color formats).
I‘ve started looking for other formats, like CMYK, when I was learning how to add cool design-time support to my custom controls.
But, I quickly understood the utilities I was coding would be more than useful in other projects, like my SVG editor.
That‘s why I publish this series of 3 articles. The proposed article content will be as follows:
"Color (or colour, see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, yellow, white, etc. Color derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra."
"Colorimetry is the science that describes colors in numbers, or provides a physical color match using a variety of measurement instruments. Colorimetry is used in chemistry, and in industries such as color printing, textile manufacturing, paint manufacturing and in the food industry."
Colorimetry definition, Wikipedia.
Then, how can we display colors as numbers? the answer: color models.
The RGB (Red, Green, Blue) color model is the most known, and the most used every day. It defines a color space in terms of three components:
The RGB color model is an additive one. In other words, Red, Green and Blue values (known as the three primary colors) are combined to reproduce other colors.
For example, the color "Red" can be represented as [R=255, G=0, B=0], "Violet" as [R=238, G=130, B=238], etc.
Its common graphic representation is the following image:
In .NET, the Color
structure use this model to provide color support through R, G and B properties.
Console.WriteLine(String.Format("R={0}, G={1}, B={2}",
Color.Red.R, Color.Red.G, Color.Red.B);
Console.WriteLine(String.Format("R={0}, G={1}, B={2}",
Color.Cyan.R, Color.Cyan.G, Color.Cyan.B);
Console.WriteLine(String.Format("R={0}, G={1}, B={2}",
Color.White.R, Color.White.G, Color.White.B);
Console.WriteLine(String.Format("R={0}, G={1}, B={2}",
Color.SteelBlue.R, Color.SteelBlue.G, Color.SteelBlue.B);
// etc...
but this is not its only usage. For this reason, we can define a dedicated RGB structure for further coding, as shown below:
/// <summary>
/// RGB structure.
/// </summary>
public struct RGB
{
/// <summary>
/// Gets an empty RGB structure;
/// </summary>
public static readonly RGB Empty = new RGB();
private int red;
private int green;
private int blue;
public static bool operator ==(RGB item1, RGB item2)
{
return (
item1.Red == item2.Red
&& item1.Green == item2.Green
&& item1.Blue == item2.Blue
);
}
public static bool operator !=(RGB item1, RGB item2)
{
return (
item1.Red != item2.Red
|| item1.Green != item2.Green
|| item1.Blue != item2.Blue
);
}
/// <summary>
/// Gets or sets red value.
/// </summary>
public int Red
{
get
{
return red;
}
set
{
red = (value>255)? 255 : ((value<0)?0 : value);
}
}
/// <summary>
/// Gets or sets red value.
/// </summary>
public int Green
{
get
{
return green;
}
set
{
green = (value>255)? 255 : ((value<0)?0 : value);
}
}
/// <summary>
/// Gets or sets red value.
/// </summary>
public int Blue
{
get
{
return blue;
}
set
{
blue = (value>255)? 255 : ((value<0)?0 : value);
}
}
public RGB(int R, int G, int B)
{
this.red = (R>255)? 255 : ((R<0)?0 : R);
this.green = (G>255)? 255 : ((G<0)?0 : G);
this.blue = (B>255)? 255 : ((B<0)?0 : B);
}
public override bool Equals(Object obj)
{
if(obj==null || GetType()!=obj.GetType()) return false;
return (this == (RGB)obj);
}
public override int GetHashCode()
{
return Red.GetHashCode() ^ Green.GetHashCode() ^ Blue.GetHashCode();
}
}
The HSB (Hue, Saturation, Brightness) color model defines a color space in terms of three constituent components:
Its common graphic representation is the following image:
The HSB model is also known as HSV (Hue, Saturation, Value) model. The HSV model was created in 1978 by Alvy Ray Smith. It is a nonlinear transformation of the RGB color space. In other words, color is not defined as a simple combination (addition/substraction) of primary colors but as a mathematical transformation.
Note: HSV and HSB are the same, but HSL is different.
All this said, a HSB structure can be :
/// <summary>
/// Structure to define HSB.
/// </summary>
public struct HSB
{
/// <summary>
/// Gets an empty HSB structure;
/// </summary>
public static readonly HSB Empty = new HSB();
private double hue;
private double saturation;
private double brightness;
public static bool operator ==(HSB item1, HSB item2)
{
return (
item1.Hue == item2.Hue
&& item1.Saturation == item2.Saturation
&& item1.Brightness == item2.Brightness
);
}
public static bool operator !=(HSB item1, HSB item2)
{
return (
item1.Hue != item2.Hue
|| item1.Saturation != item2.Saturation
|| item1.Brightness != item2.Brightness
);
}
/// <summary>
/// Gets or sets the hue component.
/// </summary>
public double Hue
{
get
{
return hue;
}
set
{
hue = (value>360)? 360 : ((value<0)?0:value);
}
}
/// <summary>
/// Gets or sets saturation component.
/// </summary>
public double Saturation
{
get
{
return saturation;
}
set
{
saturation = (value>1)? 1 : ((value<0)?0:value);
}
}
/// <summary>
/// Gets or sets the brightness component.
/// </summary>
public double Brightness
{
get
{
return brightness;
}
set
{
brightness = (value>1)? 1 : ((value<0)? 0 : value);
}
}
/// <summary>
/// Creates an instance of a HSB structure.
/// </summary>
/// <param name="h">Hue value.</param>
/// <param name="s">Saturation value.</param>
/// <param name="b">Brightness value.</param>
public HSB(double h, double s, double b)
{
hue = (h>360)? 360 : ((h<0)?0:h);
saturation = (s>1)? 1 : ((s<0)?0:s);
brightness = (b>1)? 1 : ((b<0)?0:b);
}
public override bool Equals(Object obj)
{
if(obj==null || GetType()!=obj.GetType()) return false;
return (this == (HSB)obj);
}
public override int GetHashCode()
{
return Hue.GetHashCode() ^ Saturation.GetHashCode() ^
Brightness.GetHashCode();
}
}
The HSL color space, also called HLS or HSI, stands for:
Its common graphic representation is the following image:
HSL is similar to HSB. The main difference is that HSL is symmetrical to lightness and darkness. This means that:
For my part, HSL offers a more accurate (even if it‘s not absolute) color approximation than HSB.
All this said, a HSL structure can be:
/// <summary>
/// Structure to define HSL.
/// </summary>
public struct HSL
{
/// <summary>
/// Gets an empty HSL structure;
/// </summary>
public static readonly HSL Empty = new HSL();
private double hue;
private double saturation;
private double luminance;
public static bool operator ==(HSL item1, HSL item2)
{
return (
item1.Hue == item2.Hue
&& item1.Saturation == item2.Saturation
&& item1.Luminance == item2.Luminance
);
}
public static bool operator !=(HSL item1, HSL item2)
{
return (
item1.Hue != item2.Hue
|| item1.Saturation != item2.Saturation
|| item1.Luminance != item2.Luminance
);
}
/// <summary>
/// Gets or sets the hue component.
/// </summary>
public double Hue
{
get
{
return hue;
}
set
{
hue = (value>360)? 360 : ((value<0)?0:value);
}
}
/// <summary>
/// Gets or sets saturation component.
/// </summary>
public double Saturation
{
get
{
return saturation;
}
set
{
saturation = (value>1)? 1 : ((value<0)?0:value);
}
}
/// <summary>
/// Gets or sets the luminance component.
/// </summary>
public double Luminance
{
get
{
return luminance;
}
set
{
luminance = (value>1)? 1 : ((value<0)? 0 : value);
}
}
/// <summary>
/// Creates an instance of a HSL structure.
/// </summary>
/// <param name="h">Hue value.</param>
/// <param name="s">Saturation value.</param>
/// <param name="l">Lightness value.</param>
public HSL(double h, double s, double l)
{
this.hue = (h>360)? 360 : ((h<0)?0:h);
this.saturation = (s>1)? 1 : ((s<0)?0:s);
this.luminance = (l>1)? 1 : ((l<0)?0:l);
}
public override bool Equals(Object obj)
{
if(obj==null || GetType()!=obj.GetType()) return false;
return (this == (HSL)obj);
}
public override int GetHashCode()
{
return Hue.GetHashCode() ^ Saturation.GetHashCode() ^
Luminance.GetHashCode();
}
}
The CMYK color space, also known as CMJN, stands for:
It is a subtractive color model used in color printing. CMYK works on an optical illusion that is based on light absorption.
The principle is to superimpose three images; one for cyan, one for magenta and one for yellow; which will reproduce colors.
Its common graphic representation is the following image:
Like the RGB color model, CMYK is a combination of primary colors (cyan, magenta, yellow and black). It is, probably, the only thing they have in common.
CMYK
suffers from a lack of color shades that causes holes in the color
spectrum it can reproduce. That‘s why there are often differencies when
someone convert a color between CMYK to RGB.
Why using this model? Why black is used? you can tell me... Well it‘s only for practical purpose. Wikipedia said:
Let‘s come back to our reality. A CMYK structure can be:
/// <summary>
/// Structure to define CMYK.
/// </summary>
public struct CMYK
{
/// <summary>
/// Gets an empty CMYK structure;
/// </summary>
public readonly static CMYK Empty = new CMYK();
private double c;
private double m;
private double y;
private double k;
public static bool operator ==(CMYK item1, CMYK item2)
{
return (
item1.Cyan == item2.Cyan
&& item1.Magenta == item2.Magenta
&& item1.Yellow == item2.Yellow
&& item1.Black == item2.Black
);
}
public static bool operator !=(CMYK item1, CMYK item2)
{
return (
item1.Cyan != item2.Cyan
|| item1.Magenta != item2.Magenta
|| item1.Yellow != item2.Yellow
|| item1.Black != item2.Black
);
}
public double Cyan
{
get
{
return c;
}
set
{
c = value;
c = (c>1)? 1 : ((c<0)? 0 : c);
}
}
public double Magenta
{
get
{
return m;
}
set
{
m = value;
m = (m>1)? 1 : ((m<0)? 0 : m);
}
}
public double Yellow
{
get
{
return y;
}
set
{
y = value;
y = (y>1)? 1 : ((y<0)? 0 : y);
}
}
public double Black
{
get
{
return k;
}
set
{
k = value;
k = (k>1)? 1 : ((k<0)? 0 : k);
}
}
/// <summary>
/// Creates an instance of a CMYK structure.
/// </summary>
public CMYK(double c, double m, double y, double k)
{
this.c = c;
this.m = m;
this.y = y;
this.k = k;
}
public override bool Equals(Object obj)
{
if(obj==null || GetType()!=obj.GetType()) return false;
return (this == (CMYK)obj);
}
public override int GetHashCode()
{
return Cyan.GetHashCode() ^
Magenta.GetHashCode() ^ Yellow.GetHashCode() ^ Black.GetHashCode();
}
}
The YUV model defines a color space in terms of one luma and two chrominance components. The YUV color model is used in the PAL, NTSC, and SECAM composite color video standards.
YUV models human perception of color more closely than the standard RGB model used in computer graphics hardware.
The YUV color space stands for:
A graphic representation is the following image:
A YUV structure can be:
/// <summary>
/// Structure to define YUV.
/// </summary>
public struct YUV
{
/// <summary>
/// Gets an empty YUV structure.
/// </summary>
public static readonly YUV Empty = new YUV();
private double y;
private double u;
private double v;
public static bool operator ==(YUV item1, YUV item2)
{
return (
item1.Y == item2.Y
&& item1.U == item2.U
&& item1.V == item2.V
);
}
public static bool operator !=(YUV item1, YUV item2)
{
return (
item1.Y != item2.Y
|| item1.U != item2.U
|| item1.V != item2.V
);
}
public double Y
{
get
{
return y;
}
set
{
y = value;
y = (y>1)? 1 : ((y<0)? 0 : y);
}
}
public double U
{
get
{
return u;
}
set
{
u = value;
u = (u>0.436)? 0.436 : ((u<-0.436)? -0.436 : u);
}
}
public double V
{
get
{
return v;
}
set
{
v = value;
v = (v>0.615)? 0.615 : ((v<-0.615)? -0.615 : v);
}
}
/// <summary>
/// Creates an instance of a YUV structure.
/// </summary>
public YUV(double y, double u, double v)
{
this.y = (y>1)? 1 : ((y<0)? 0 : y);
this.u = (u>0.436)? 0.436 : ((u<-0.436)? -0.436 : u);
this.v = (v>0.615)? 0.615 : ((v<-0.615)? -0.615 : v);
}
public override bool Equals(Object obj)
{
if(obj==null || GetType()!=obj.GetType()) return false;
return (this == (YUV)obj);
}
public override int GetHashCode()
{
return Y.GetHashCode() ^ U.GetHashCode() ^ V.GetHashCode();
}
}
In opposition to the previous models, the CIE XYZ model defines an absolute color space. It is also known as the CIE 1931 XYZ color space and stands for:
Before trying to explain why I include this color space in this article, you have to know that it‘s one of the first standards created by the International Commission on Illumination (CIE) in 1931. It is based on direct measurements of the human eye, and serves as the basis from which many other color spaces are defined.
A graphic representation is the following image:
A CIE XYZ structure can be:
/// <summary>
/// Structure to define CIE XYZ.
/// </summary>
public struct CIEXYZ
{
/// <summary>
/// Gets an empty CIEXYZ structure.
/// </summary>
public static readonly CIEXYZ Empty = new CIEXYZ();
/// <summary>
/// Gets the CIE D65 (white) structure.
/// </summary>
public static readonly CIEXYZ D65 = new CIEXYZ(0.9505, 1.0, 1.0890);
private double x;
private double y;
private double z;
public static bool operator ==(CIEXYZ item1, CIEXYZ item2)
{
return (
item1.X == item2.X
&& item1.Y == item2.Y
&& item1.Z == item2.Z
);
}
public static bool operator !=(CIEXYZ item1, CIEXYZ item2)
{
return (
item1.X != item2.X
|| item1.Y != item2.Y
|| item1.Z != item2.Z
);
}
/// <summary>
/// Gets or sets X component.
/// </summary>
public double X
{
get
{
return this.x;
}
set
{
this.x = (value>0.9505)? 0.9505 : ((value<0)? 0 : value);
}
}
/// <summary>
/// Gets or sets Y component.
/// </summary>
public double Y
{
get
{
return this.y;
}
set
{
this.y = (value>1.0)? 1.0 : ((value<0)?0 : value);
}
}
/// <summary>
/// Gets or sets Z component.
/// </summary>
public double Z
{
get
{
return this.z;
}
set
{
this.z = (value>1.089)? 1.089 : ((value<0)? 0 : value);
}
}
public CIEXYZ(double x, double y, double z)
{
this.x = (x>0.9505)? 0.9505 : ((x<0)? 0 : x);
this.y = (y>1.0)? 1.0 : ((y<0)? 0 : y);
this.z = (z>1.089)? 1.089 : ((z<0)? 0 : z);
}
public override bool Equals(Object obj)
{
if(obj==null || GetType()!=obj.GetType()) return false;
return (this == (CIEXYZ)obj);
}
public override int GetHashCode()
{
return X.GetHashCode() ^ Y.GetHashCode() ^ Z.GetHashCode();
}
}
Well! why do I have to include this model?
I have made a quick research to include Cie L*a*b* color model in this article, and I find that a conversion to an absolute color space is required before converting to L*a*b*. The model used in the conversion principle is Cie XYZ. So, I‘ve included it and now everyone can understand "what are those XYZ values" used further in the article.
"A Lab color space is a color-opponent space with dimension L for luminance and a and b for the color-opponent dimensions, based on nonlinearly-compressed CIE XYZ color space coordinates."
As said in the previous definition, CIE L*a*b* color space, also know as CIE 1976 color space, stands for:
The L*a*b* color model has been created to serve as a device independent model to be used as a reference. It is based directly on the CIE 1931 XYZ color space as an attempt to linearize the perceptibility of color differences.
The non-linear relations for L*, a*, and b* are intended to mimic the logarithmic response of the eye, coloring information is referred to the color of the white point of the system.
A CIE L*a*b* structure can be:
/// <summary>
/// Structure to define CIE L*a*b*.
/// </summary>
public struct CIELab
{
/// <summary>
/// Gets an empty CIELab structure.
/// </summary>
public static readonly CIELab Empty = new CIELab();
private double l;
private double a;
private double b;
public static bool operator ==(CIELab item1, CIELab item2)
{
return (
item1.L == item2.L
&& item1.A == item2.A
&& item1.B == item2.B
);
}
public static bool operator !=(CIELab item1, CIELab item2)
{
return (
item1.L != item2.L
|| item1.A != item2.A
|| item1.B != item2.B
);
}
/// <summary>
/// Gets or sets L component.
/// </summary>
public double L
{
get
{
return this.l;
}
set
{
this.l = value;
}
}
/// <summary>
/// Gets or sets a component.
/// </summary>
public double A
{
get
{
return this.a;
}
set
{
this.a = value;
}
}
/// <summary>
/// Gets or sets a component.
/// </summary>
public double B
{
get
{
return this.b;
}
set
{
this.b = value;
}
}
public CIELab(double l, double a, double b)
{
this.l = l;
this.a = a;
this.b = b;
}
public override bool Equals(Object obj)
{
if(obj==null || GetType()!=obj.GetType()) return false;
return (this == (CIELab)obj);
}
public override int GetHashCode()
{
return L.GetHashCode() ^ a.GetHashCode() ^ b.GetHashCode();
}
}
There are still many other formats like RYB and CcMmYK. I still don‘t intend to create a "color framework", but if you have other ideas...
Converting RGB color to any other model is the basis in conversion algorithms. It implies a normalisation of red, green and blue : value ranges now from [0..255]
to [0..1]
.
The conversion principle is the one below:
H ? [0, 360]
S, V, R, G, B ? [0, 1]
V = MAX
Well! Interesting! But what‘s the C# equivalent? Here it is.
/// <summary>
/// Converts RGB to HSB.
/// </summary>
public static HSB RGBtoHSB(int red, int green, int blue)
{
// normalize red, green and blue values
double r = ((double)red/255.0);
double g = ((double)green/255.0);
double b = ((double)blue/255.0);
// conversion start
double max = Math.Max(r, Math.Max(g, b));
double min = Math.Min(r, Math.Min(g, b));
double h = 0.0;
if(max==r && g>=b)
{
h = 60 * (g-b)/(max-min);
}
else if(max==r && g < b)
{
h = 60 * (g-b)/(max-min) + 360;
}
else if(max == g)
{
h = 60 * (b-r)/(max-min) + 120;
}
else if(max == b)
{
h = 60 * (r-g)/(max-min) + 240;
}
double s = (max == 0)? 0.0 : (1.0 - (min/max));
return new HSB(h, s, (double)max);
}
The conversion principle is the one below:
H ? [0, 360]
S, L, R, G, B ? [0, 1]
L = ½(MAX + MIN)
The C# equivalent is:
/// <summary>
/// Converts RGB to HSL.
/// </summary>
/// <param name="red">Red value, must be in [0,255].</param>
/// <param name="green">Green value, must be in [0,255].</param>
/// <param name="blue">Blue value, must be in [0,255].</param>
public static HSL RGBtoHSL(int red, int green, int blue)
{
double h=0, s=0, l=0;
// normalize red, green, blue values
double r = (double)red/255.0;
double g = (double)green/255.0;
double b = (double)blue/255.0;
double max = Math.Max(r, Math.Max(g, b));
double min = Math.Min(r, Math.Min(g, b));
// hue
if(max == min)
{
h = 0; // undefined
}
else if(max==r && g>=b)
{
h = 60.0*(g-b)/(max-min);
}
else if(max==r && g<b)
{
h = 60.0*(g-b)/(max-min) + 360.0;
}
else if(max==g)
{
h = 60.0*(b-r)/(max-min) + 120.0;
}
else if(max==b)
{
h = 60.0*(r-g)/(max-min) + 240.0;
}
// luminance
l = (max+min)/2.0;
// saturation
if(l == 0 || max == min)
{
s = 0;
}
else if(0<l && l<=0.5)
{
s = (max-min)/(max+min);
}
else if(l>0.5)
{
s = (max-min)/(2 - (max+min)); //(max-min > 0)?
}
return new HSL(
Double.Parse(String.Format("{0:0.##}", h)),
Double.Parse(String.Format("{0:0.##}", s)),
Double.Parse(String.Format("{0:0.##}", l))
);
}
Note: You have probably noticed String.Format("{0:0.##}", h)
... It‘s the .NET solution for keeping the same rounding behavior. If you don‘t understand what I mean, try the sample code below:
Console.WriteLine(Math.Round(4.45, 1)); // returns 4.4.
Console.WriteLine(Math.Round(4.55, 1)); // returns 4.6.
You didn‘t notice a problem? Ok, rouding 4.45 should have returned 4.5 and not 4.4. The solution is using String.Format()
which always applies "round-to-even" method.
The conversion principle is the one below :
R, G, B ? [0, 1]
tC‘M‘Y‘ = {1 - R, 1 - G, 1 - B}
K = min{C‘, M‘, Y‘}
tCMYK = {0, 0, 0, 1} if K = 1
tCMYK = { (C‘ - K)/(1 - K), (M‘ - K)/(1 - K), (Y‘ - K)/(1 - K), K } otherwise
The C# equivalent is:
/// <summary>
/// Converts RGB to CMYK.
/// </summary>
/// <param name="red">Red vaue must be in [0, 255]. </param>
/// <param name="green">Green vaue must be in [0, 255].</param>
/// <param name="blue">Blue vaue must be in [0, 255].</param>
public static CMYK RGBtoCMYK(int red, int green, int blue)
{
// normalizes red, green, blue values
double c = (double)(255 - red)/255;
double m = (double)(255 - green)/255;
double y = (double)(255 - blue)/255;
double k = (double)Math.Min(c, Math.Min(m, y));
if(k == 1.0)
{
return new CMYK(0,0,0,1);
}
else
{
return new CMYK((c-k)/(1-k), (m-k)/(1-k), (y-k)/(1-k), k);
}
}
The conversion principle is the one below :
R, G, B, Y ? [0, 1]
U ? [-0.436, 0.436]
V ? [-0.615, 0.615]
tYUV = { (0.299 R + 0.587 G + 0.114 B), (- 0.14713 R + 0.28886 G + 0.436 B), (0.615 R + 0.51499 G + 0.10001 B) }
The C# equivalent is :
/// <summary>
/// Converts RGB to YUV.
/// </summary>
/// <param name="red">Red must be in [0, 255].</param>
/// <param name="green">Green must be in [0, 255].</param>
/// <param name="blue">Blue must be in [0, 255].</param>
public static YUV RGBtoYUV(int red, int green, int blue)
{
YUV yuv = new YUV();
// normalizes red, green, blue values
double r = (double)red/255.0;
double g = (double)green/255.0;
double b = (double)blue/255.0;
yuv.Y = 0.299*r + 0.587*g + 0.114*b;
yuv.U = -0.14713*r -0.28886*g + 0.436*b;
yuv.V = 0.615*r -0.51499*g -0.10001*b;
return yuv;
}
Haaa! Something I can explain.
As you probably already know, web colors can be defined in two ways: for example, "red" can be defined as rgb(255,0,0)
or #FF0000
.
The explanation of the second form is simple :
#
" character tells that the format is the hexadecimal one.So, you can divide each color component by 16 and replace numbers superior to 9 by theirs hexadecimal value (eg. 10 = A, 11 = B, etc.)... but the best way is to use String.Format()
habilities.
/// <summary>
/// Converts a RGB color format to an hexadecimal color.
/// </summary>
/// <param name="r">Red value.</param>
/// <param name="g">Green value.</param>
/// <param name="b">Blue value.</param>
public static string RGBToHex(int r, int g, int b)
{
return String.Format("#{0:x2}{1:x2}{2:x2}", r, g, b).ToUpper();
}
The conversion principle is the one below:
R, G, B ? [0, 1]
a = 0.055 and ? ˜ 2.2
where
The C# equivalent is :
/// <summary>
/// Converts RGB to CIE XYZ (CIE 1931 color space)
/// </summary>
public static CIEXYZ RGBtoXYZ(int red, int green, int blue)
{
// normalize red, green, blue values
double rLinear = (double)red/255.0;
double gLinear = (double)green/255.0;
double bLinear = (double)blue/255.0;
// convert to a sRGB form
double r = (rLinear > 0.04045)? Math.Pow((rLinear + 0.055)/(
1 + 0.055), 2.2) : (rLinear/12.92) ;
double g = (gLinear > 0.04045)? Math.Pow((gLinear + 0.055)/(
1 + 0.055), 2.2) : (gLinear/12.92) ;
double b = (bLinear > 0.04045)? Math.Pow((bLinear + 0.055)/(
1 + 0.055), 2.2) : (bLinear/12.92) ;
// converts
return new CIEXYZ(
(r*0.4124 + g*0.3576 + b*0.1805),
(r*0.2126 + g*0.7152 + b*0.0722),
(r*0.0193 + g*0.1192 + b*0.9505)
);
}
As I said before, converting to the CIE L*a*b color model is a little bit tricky: we need to convert to CIE XYZ before trying to have L*a*b* values.
/// <summary>
/// Converts RGB to CIELab.
/// </summary>
public static CIELab RGBtoLab(int red, int green, int blue)
{
return XYZtoLab( RGBtoXYZ(red, green, blue) );
}
The conversion between XYZ and L*a*b* is given below.
The conversion principle is the one below :
H ? [0, 360]
S, V, R, G, B ? [0, 1]
Hi = [H / 60] mod 6
f = (H / 60) - Hi
p = V (1 - S)
q = V (1 - f S)
t = V (1 - (1 - f ) S)
if Hi = 0 ? R = V, G = t, B = p
if Hi = 1 ? R = q, G = V, B = p
if Hi = 2 ? R = p, G = V, B = t
if Hi = 3 ? R = p, G = q, B = V
if Hi = 4 ? R = t, G = p, B = V
if Hi = 5 ? R = V, G = p, B = q
The C# equivalent? Here it is.
/// <summary>
/// Converts HSB to RGB.
/// </summary>
public static RGB HSBtoRGB(double h, double s, double b)
{
double r = 0;
double g = 0;
double b = 0;
if(s == 0)
{
r = g = b = b;
}
else
{
// the color wheel consists of 6 sectors. Figure out which sector
// you‘re in.
double sectorPos = h / 60.0;
int sectorNumber = (int)(Math.Floor(sectorPos));
// get the fractional part of the sector
double fractionalSector = sectorPos - sectorNumber;
// calculate values for the three axes of the color.
double p = b * (1.0 - s);
double q = b * (1.0 - (s * fractionalSector));
double t = b * (1.0 - (s * (1 - fractionalSector)));
// assign the fractional colors to r, g, and b based on the sector
// the angle is in.
switch(sectorNumber)
{
case 0:
r = b;
g = t;
b = p;
break;
case 1:
r = q;
g = b;
b = p;
break;
case 2:
r = p;
g = b;
b = t;
break;
case 3:
r = p;
g = q;
b = b;
break;
case 4:
r = t;
g = p;
b = b;
break;
case 5:
r = b;
g = p;
b = q;
break;
}
}
return new RGB(
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}", r*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}", g*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}", b*255.0)) )
);
}
Conversion principle is quite simple (but not accurate): convert to RGB and then to HSL.
/// <summary>
/// Converts HSB to HSL.
/// </summary>
public static HSL HSBtoHSL(double h, double s, double b)
{
RGB rgb = HSBtoRGB(h, s, b);
return RGBtoHSL(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new : conversion principle is to convert to RGB and then to CMYK.
/// <summary>
/// Converts HSB to CMYK.
/// </summary>
public static CMYK HSBtoCMYK(double h, double s, double b)
{
RGB rgb = HSBtoRGB(h, s, b);
return RGBtoCMYK(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new : conversion principle is to convert to RGB and then to YUV.
/// <summary>
/// Converts HSB to CMYK.
/// </summary>
public static YUV HSBtoYUV(double h, double s, double b)
{
RGB rgb = HSBtoRGB(h, s, b);
return RGBtoYUV(rgb.Red, rgb.Green, rgb.Blue);
}
The conversion principle is the one below :
H ? [0, 360]
S, L, R, G, B ? [0, 1]
if L < 0.5 ? Q = L × (1 + S)
if L = 0.5 ? Q = L + S – (L × S)
P = 2 × L – Q
Hk = H / 360
Tr = Hk + 1/3
Tg = Hk
Tb = Hk – 1/3
For each c = R,G,B :
if Tc < 0 ? Tc = Tc + 1.0
if Tc > 1 ? Tc = Tc – 1.0
if Tc < 1/6 ? Tc = P + ((Q – P) × 6.0 × Tc)
if 1/6 = Tc > 1/2 ? Tc = Q
if 1/2 = Tc > 2/3 ? Tc = P + ((Q – P) × (2/3 – Tc) × 6.0)
else Tc = P
The C# equivalent? Here it is.
/// <summary>
/// Converts HSL to RGB.
/// </summary>
/// <param name="h">Hue, must be in [0, 360].</param>
/// <param name="s">Saturation, must be in [0, 1].</param>
/// <param name="l">Luminance, must be in [0, 1].</param>
public static RGB HSLtoRGB(double h, double s, double l)
{
if(s == 0)
{
// achromatic color (gray scale)
return new RGB(
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
l*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
l*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
l*255.0)) )
);
}
else
{
double q = (l<0.5)?(l * (1.0+s)):(l+s - (l*s));
double p = (2.0 * l) - q;
double Hk = h/360.0;
double[] T = new double[3];
T[0] = Hk + (1.0/3.0); // Tr
T[1] = Hk; // Tb
T[2] = Hk - (1.0/3.0); // Tg
for(int i=0; i<3; i++)
{
if(T[i] < 0) T[i] += 1.0;
if(T[i] > 1) T[i] -= 1.0;
if((T[i]*6) < 1)
{
T[i] = p + ((q-p)*6.0*T[i]);
}
else if((T[i]*2.0) < 1) //(1.0/6.0)<=T[i] && T[i]<0.5
{
T[i] = q;
}
else if((T[i]*3.0) < 2) // 0.5<=T[i] && T[i]<(2.0/3.0)
{
T[i] = p + (q-p) * ((2.0/3.0) - T[i]) * 6.0;
}
else T[i] = p;
}
return new RGB(
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
T[0]*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
T[1]*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
T[2]*255.0)) )
);
}
}
Nothing new: conversion principle is to convert to RGB and then to HSB.
/// <summary>
/// Converts HSL to HSB.
/// </summary>
public static HSB HSLtoHSB(double h, double s, double l)
{
RGB rgb = HSLtoRGB(h, s, l);
return RGBtoHSB(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new: conversion principle is to convert to RGB and then to CMYK.
/// <summary>
/// Converts HSL to CMYK.
/// </summary>
public static CMYK HSLtoCMYK(double h, double s, double l)
{
RGB rgb = HSLtoRGB(h, s, l);
return RGBtoCMYK(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new: conversion principle is to convert to RGB and then to CMYK.
/// <summary>
/// Converts HSL to YUV.
/// </summary>
public static YUV HSLtoYUV(double h, double s, double l)
{
RGB rgb = HSLtoRGB(h, s, l);
return RGBtoYUV(rgb.Red, rgb.Green, rgb.Blue);
}
The conversion principle is the one below:
tRGB = { (1 - C) × (1 - K) , (1 - M) × (1 - K), (1 - Y) × (1 - K)}
The C# equivalent? Here it is.
/// <summary>
/// Converts CMYK to RGB.
/// </summary>
public static Color CMYKtoRGB(double c, double m, double y, double k)
{
int red = Convert.ToInt32((1-c) * (1-k) * 255.0);
int green = Convert.ToInt32((1-m) * (1-k) * 255.0);
int blue = Convert.ToInt32((1-y) * (1-k) * 255.0);
return Color.FromArgb(red, green, blue);
}
Nothing new: conversion principle is to convert to RGB and then to HSL.
/// <summary>
/// Converts CMYK to HSL.
/// </summary>
public static HSL CMYKtoHSL(double c, double m, double y, double k)
{
RGB rgb = CMYKtoRGB(c, m, y, k);
return RGBtoHSL(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new: conversion principle is to convert to RGB and then to HSB.
/// <summary>
/// Converts CMYK to HSB.
/// </summary>
public static HSB CMYKtoHSB(double c, double m, double y, double k)
{
RGB rgb = CMYKtoRGB(c, m, y, k);
return RGBtoHSB(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new: conversion principle is to convert to RGB and then to YUV.
/// <summary>
/// Converts CMYK to YUV.
/// </summary>
public static YUV CMYKtoYUV(double c, double m, double y, double k)
{
RGB rgb = CMYKtoRGB(c, m, y, k);
return RGBtoYUV(rgb.Red, rgb.Green, rgb.Blue);
}
The conversion principle is the one below:
R, G, B, Y ? [0, 1]
U ? [-0.436, 0.436]
V ? [-0.615, 0.615]
tRGB = { (Y + 1.13983 V), (Y - 0.39466 U - 0.58060 V), (Y + 2.03211 U) }
The C# equivalent is :
/// <summary>
/// Converts YUV to RGB.
/// </summary>
/// <param name="y">Y must be in [0, 1].</param>
/// <param name="u">U must be in [-0.436, +0.436].</param>
/// <param name="v">V must be in [-0.615, +0.615].</param>
public static RGB YUVtoRGB(double y, double u, double v)
{
RGB rgb = new RGB();
rgb.Red = Convert.ToInt32((y + 1.139837398373983740*v)*255);
rgb.Green = Convert.ToInt32((
y - 0.3946517043589703515*u - 0.5805986066674976801*v)*255);
rgb.Blue = Convert.ToInt32((y + 2.032110091743119266*u)*255);
return rgb;
}
Nothing new: conversion principle is to convert to RGB and then to HSL.
/// <summary>
/// Converts YUV to HSL.
/// </summary>
/// <param name="y">Y must be in [0, 1].</param>
/// <param name="u">U must be in [-0.436, +0.436].</param>
/// <param name="v">V must be in [-0.615, +0.615].</param>
public static HSL YUVtoHSL(double y, double u, double v)
{
RGB rgb = YUVtoRGB(y, u, v);
return RGBtoHSL(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new: conversion principle is to convert to RGB and then to HSB.
/// <summary>
/// Converts YUV to HSB.
/// </summary>
/// <param name="y">Y must be in [0, 1].</param>
/// <param name="u">U must be in [-0.436, +0.436].</param>
/// <param name="v">V must be in [-0.615, +0.615].</param>
public static HSB YUVtoHSB(double y, double u, double v)
{
RGB rgb = YUVtoRGB(y, u, v);
return RGBtoHSB(rgb.Red, rgb.Green, rgb.Blue);
}
Nothing new: conversion principle is to convert to RGB and then to CMYK.
/// <summary>
/// Converts YUV to CMYK.
/// </summary>
/// <param name="y">Y must be in [0, 1].</param>
/// <param name="u">U must be in [-0.436, +0.436].</param>
/// <param name="v">V must be in [-0.615, +0.615].</param>
public static CMYK YUVtoCMYK(double y, double u, double v)
{
RGB rgb = YUVtoRGB(y, u, v);
return RGBtoCMYK(rgb.Red, rgb.Green, rgb.Blue);
}
The conversion principle is the one below:
a = 0.055
then
The C# equivalent is :
/// <summary>
/// Converts CIEXYZ to RGB structure.
/// </summary>
public static RGB XYZtoRGB(double x, double y, double z)
{
double[] Clinear = new double[3];
Clinear[0] = x*3.2410 - y*1.5374 - z*0.4986; // red
Clinear[1] = -x*0.9692 + y*1.8760 - z*0.0416; // green
Clinear[2] = x*0.0556 - y*0.2040 + z*1.0570; // blue
for(int i=0; i<3; i++)
{
Clinear[i] = (Clinear[i]<=0.0031308)? 12.92*Clinear[i] : (
1+0.055)* Math.Pow(Clinear[i], (1.0/2.4)) - 0.055;
}
return new RGB(
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
Clinear[0]*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
Clinear[1]*255.0)) ),
Convert.ToInt32( Double.Parse(String.Format("{0:0.00}",
Clinear[2]*255.0)) )
);
}
The conversion principle is the one below:
Xn, Yn and Zn are the CIE XYZ tristimulus values of the reference white point.
The C# equivalent is:
/// <summary>
/// XYZ to L*a*b* transformation function.
/// </summary>
private static double Fxyz(double t)
{
return ((t > 0.008856)? Math.Pow(t, (1.0/3.0)) : (7.787*t + 16.0/116.0));
}
/// <summary>
/// Converts CIEXYZ to CIELab.
/// </summary>
public static CIELab XYZtoLab(double x, double y, double z)
{
CIELab lab = CIELab.Empty;
lab.L = 116.0 * Fxyz( y/CIEXYZ.D65.Y ) -16;
lab.A = 500.0 * (Fxyz( x/CIEXYZ.D65.X ) - Fxyz( y/CIEXYZ.D65.Y) );
lab.B = 200.0 * (Fxyz( y/CIEXYZ.D65.Y ) - Fxyz( z/CIEXYZ.D65.Z) );
return lab;
}
The conversion principle is the one below:
d = 6/29
The C# equivalent is:
/// <summary>
/// Converts CIELab to CIEXYZ.
/// </summary>
public static CIEXYZ LabtoXYZ(double l, double a, double b)
{
double delta = 6.0/29.0;
double fy = (l+16)/116.0;
double fx = fy + (a/500.0);
double fz = fy - (b/200.0);
return new CIEXYZ(
(fx > delta)? CIEXYZ.D65.X * (fx*fx*fx) : (fx - 16.0/116.0)*3*(
delta*delta)*CIEXYZ.D65.X,
(fy > delta)? CIEXYZ.D65.Y * (fy*fy*fy) : (fy - 16.0/116.0)*3*(
delta*delta)*CIEXYZ.D65.Y,
(fz > delta)? CIEXYZ.D65.Z * (fz*fz*fz) : (fz - 16.0/116.0)*3*(
delta*delta)*CIEXYZ.D65.Z
);
}
Nothing really new, the principle is to convert to XYZ and then to RGB :
/// <summary>
/// Converts CIELab to RGB.
/// </summary>
public static RGB LabtoRGB(double l, double a, double b)
{
return XYZtoRGB( LabtoXYZ(l, a, b) );
}
Well, after showing you the conversion algorithms, maybe there is nothing more I can tell you.
In fact, there are many other useful methods in ColorSpaceHelper
. You will find:
ColorSpaceHelper.GetColorDistance()
).ColorSpaceHelper.GetWheelColors()
) with 32bit support (alpha).ColorSpaceHelper.GetSpectrumColors()
) with 32bit support (alpha).ColorSpaceHelper.HexToColor()
).System.Drawing.Color
and the other structures.
Like I said before, there are many formats. This article gives you an example of how using common color models (RGB, HSL, HSB, etc.) perhaps will help you in your own projects.
Here is a preview of what we can do (and what we will see in the next article) with ColorSpaceHelper
:
标签:
原文地址:http://www.cnblogs.com/Free-Thinker/p/4950364.html