I need an algorithm or function to map each wavelength of visible range of spectrum to its equivalent RGB values. 
Is there any structural relation between the RGB System and wavelength of a light? 
like this image:
[![alt text][1]][1]  
&lt;sub&gt;(source: [kms at www1.appstate.edu](http://www1.appstate.edu/~kms/classes/psy3203/Color/spectrum5.gif))&lt;/sub&gt;  

*sorry if this was irrelevant :-]*

  [1]: https://i.stack.imgur.com/fJ0uO.gif

RGB values of visible spectrum

I would like to get the RGB Value of an UIColor in Swift:

    let swiftColor = UIColor(red: 1, green: 165/255, blue: 0, alpha: 1)
    println(&quot;RGB Value is:&quot;);
    println(swiftColor.getRGB()); &lt;&lt;&lt;&lt;&lt;&lt; How to do that ?

In Java I would do it as follows:

    Color cnew = new Color();
    int iColor = cnew.rgb(1, 165/255, 0);
    System.out.println(iColor);

How should I get this value?

How to get the RGB Code (INT) from an UIColor in Swift

I have some code that generates image of a pie chart. It&#39;s a general purpose class, so any number of slices can be given as input. Now I have problem picking good colors for the slices. Is there some algorithm that is good at that?

Colors need to follow some rules:

- they need to look nice
- adjacent colors should not be similar (blue next to green is a no-go)
- pie background color is white, so white is out of option

Some algorithm manipulating with RGB values would be a preferred solution.


How to pick color palette for a pie-chart?

I&#39;m creating a Color Picker tool and for the HSL slider, I need to be able to convert RGB to HSL. When I searched SO for a way to do the conversion, I found this question [HSL to RGB color conversion][1].

While it provides a function to do conversion from RGB to HSL, I see no explanation to what&#39;s really going on in the calculation. To understand it better, I&#39;ve read the [HSL and HSV][2] on Wikipedia.

Later, I&#39;ve rewritten the function from the &quot;HSL to RGB color conversion&quot; using the calculations from the &quot;HSL and HSV&quot; page.

I&#39;m stuck at the calculation of hue if the R is the max value. See the calculation from the &quot;HSL and HSV&quot; page:

[![enter image description here][3]][3]

This is from another [wiki page][4] that&#39;s in Dutch:

[![enter image description here][5]][5]

and this is from the [answers][6] to &quot;HSL to RGB color conversion&quot;:

    case r: h = (g - b) / d + (g &lt; b ? 6 : 0); break; // d = max-min = c

I&#39;ve tested all three with a few RGB values and they seem to produce similar (if not exact) results. What I&#39;m wondering is are they performing the same thing? Will get I different results for some specific RGB values? Which one should I be using?

	hue = (g - b) / c;                   // dutch wiki
	hue = ((g - b) / c) % 6;             // eng wiki
	hue = (g - b) / c + (g &lt; b ? 6 : 0); // SO answer

&lt;sub&gt;

	function rgb2hsl(r, g, b) {
		// see https://en.wikipedia.org/wiki/HSL_and_HSV#Formal_derivation
		// convert r,g,b [0,255] range to [0,1]
		r = r / 255,
		g = g / 255,
		b = b / 255;
		// get the min and max of r,g,b
		var max = Math.max(r, g, b);
		var min = Math.min(r, g, b);
		// lightness is the average of the largest and smallest color components
		var lum = (max + min) / 2;
		var hue;
		var sat;
		if (max == min) { // no saturation
			hue = 0;
			sat = 0;
		} else {
			var c = max - min; // chroma
			// saturation is simply the chroma scaled to fill
			// the interval [0, 1] for every combination of hue and lightness
			sat = c / (1 - Math.abs(2 * lum - 1));
			switch(max) {
				case r:
					// hue = (g - b) / c;
					// hue = ((g - b) / c) % 6;
					// hue = (g - b) / c + (g &lt; b ? 6 : 0);
					break;
				case g:
					hue = (b - r) / c + 2;
					break;
				case b:
					hue = (r - g) / c + 4;
					break;
			}
		}
		hue = Math.round(hue * 60); // &#176;
		sat = Math.round(sat * 100); // %
		lum = Math.round(lum * 100); // %
		return [hue, sat, lum];
	}


  [1]: https://stackoverflow.com/questions/2353211/hsl-to-rgb-color-conversion
  [2]: https://en.wikipedia.org/wiki/HSL_and_HSV
  [3]: http://i.stack.imgur.com/c6FL6.jpg
  [4]: https://nl.wikipedia.org/wiki/HSL_(kleurruimte)#Omzetting_van_RGB_naar_HSL
  [5]: http://i.stack.imgur.com/VJrSc.jpg
  [6]: https://stackoverflow.com/a/9493060/2202732

RGB to HSL conversion

What is the most efficient way to do this?

Converting hex color to RGB and vice-versa

I am looking for an algorithm to convert between HSL color to RGB. 

It seems to me that HSL is not very widely used so I am not having much luck searching for a converter.

HSL to RGB color conversion

I&#39;m trying to load a PNG image using SDL but the program doesn&#39;t work and this error appears in the console

&gt; libpng warning: iCCP: known incorrect sRGB profile

Why does this warning appear? What should I do to solve this problem?

libpng warning: iCCP: known incorrect sRGB profile

I want to design a program that can help me assess between 5 pre-defined colors which one is more similar to a variable color, and with what percentage.  The thing is that I don&#39;t know how to do that manually step by step. So it is even more difficult to think of a program.

More details: The colors are from photographs of tubes with gel that as different colors. I have 5 tubes with different colors were each is representative of 1 of 5 levels. I want to take photographs of other samples and on the computer assess to which level that sample belongs by comparing colors, and I want to know that with a percentage of approximation too. I would like a program that does something like this: http://www.colortools.net/color_matcher.html

If you can tell me what steps to take, even if they are things for me to think and do manually. It would be very helpful. 

How to compare two colors for similarity/difference

Using the following jQuery will get the RGB value of an element&#39;s background color:

    $(&#39;#selector&#39;).css(&#39;backgroundColor&#39;);

Is there a way to get the hex value rather than the RGB?

How to get hex color value rather than RGB value?

If I open an image with `open(&quot;image.jpg&quot;)`, how can I get the RGB values of a pixel assuming I have the coordinates of the pixel?

Then, how can I do the reverse of this? Starting with a blank graphic, &#39;write&#39; a pixel with a certain RGB value?

I would prefer if I didn&#39;t have to download any additional libraries.

How to read the RGB value of a given pixel in Python?

How to convert colors in RGB format to hex format and vice versa?

For example, convert `&#39;#0080C0&#39;` to `(0, 128, 192)`.

RGB to hex and hex to RGB

Using C# I was trying to develop the following two. The way I am doing it may have some problem and need your kind advice. In addition, I dont know whether there is any existing method to do the same.

    private static String HexConverter(System.Drawing.Color c)
    {
        String rtn = String.Empty;
        try
        {
            rtn = &quot;#&quot; + c.R.ToString(&quot;X2&quot;) + c.G.ToString(&quot;X2&quot;) + c.B.ToString(&quot;X2&quot;);
        }
        catch (Exception ex)
        {
            //doing nothing
        }

        return rtn;
    }

    private static String RGBConverter(System.Drawing.Color c)
    {
        String rtn = String.Empty;
        try
        {
            rtn = &quot;RGB(&quot; + c.R.ToString() + &quot;,&quot; + c.G.ToString() + &quot;,&quot; + c.B.ToString() + &quot;)&quot;;
        }
        catch (Exception ex)
        {
            //doing nothing
        }

        return rtn;
    }

Thanks.

Convert System.Drawing.Color to RGB and Hex Value

Given an RGB value, like `168, 0, 255`, how do I create tints (make it lighter) and shades (make it darker) of the color?

Given an RGB value, how do I create a tint (or shade)?

When converting from RGB to grayscale, it is said that specific weights to channels R, G, and B ought to be applied. These weights are: 0.2989, 0.5870, 0.1140.

It is said that the reason for this is different human perception/sensibility towards these three colors. Sometimes it is also said these are the values used to compute NTSC signal.

However, I didn&#39;t find a good reference for this on the web. What is the source of these values?

See also these previous questions: [here][1] and [here][2].


  [1]: https://stackoverflow.com/questions/14330/rgb-to-monochrome-conversion
  [2]: https://stackoverflow.com/questions/596216/formula-to-determine-brightness-of-rgb-color

Converting RGB to grayscale/intensity

Does anyone know of any formula for converting a light frequency to an RGB value?

Convert light frequency to RGB?

I need to convert `(0, 128, 64)` to something like this `&quot;#008040&quot;`. I&#39;m not sure what to call the latter, making searching difficult. 

Converting an RGB color tuple to a hexidecimal string

Seeing as how the three primary colors are cyan, magenta and yellow (CMY), why do monitors and almost all the GUI components out there use red, green and blue (RGB)? (If I&#39;m not mistaken, printers use the CMYK model.)

Is there a historical, hardware/software, or other reason for it?

Why rgb and not cmy?

Working off Jeremy&#39;s response here: https://stackoverflow.com/questions/214359/converting-hex-color-to-rgb-and-vice-versa I was able to get a python program to convert preset colour hex codes (example #B4FBB8), however from an end-user perspective we can&#39;t ask people to edit code &amp; run from there. How can one prompt the user to enter a hex value and then have it spit out a RGB value from there? 

Here&#39;s the code I have thus far:

    def hex_to_rgb(value):
        value = value.lstrip(&#39;#&#39;)
        lv = len(value)
        return tuple(int(value[i:i + lv // 3], 16) for i in range(0, lv, lv // 3))
    
    
    def rgb_to_hex(rgb):
        return &#39;#%02x%02x%02x&#39; % rgb
    
    hex_to_rgb(&quot;#ffffff&quot;)              # ==&gt; (255, 255, 255)
    hex_to_rgb(&quot;#ffffffffffff&quot;)        # ==&gt; (65535, 65535, 65535)
    rgb_to_hex((255, 255, 255))        # ==&gt; &#39;#ffffff&#39;
    rgb_to_hex((65535, 65535, 65535))  # ==&gt; &#39;#ffffffffffff&#39;
    
    print(&#39;Please enter your colour hex&#39;)
    
    hex == input(&quot;&quot;)
    
    print(&#39;Calculating...&#39;)
    print(hex_to_rgb(hex()))

Using the line `print(hex_to_rgb(&#39;#B4FBB8&#39;))` I&#39;m able to get it to spit out the correct RGB value which is (180, 251, 184)

It&#39;s probably super simple - I&#39;m still pretty rough with Python. 

Converting Hex to RGB value in Python

I&#39;m loading in a color image in Python OpenCV and plotting the same. However, the image I get has it&#39;s colors all mixed up. 

Here is the code:

    import cv2
	import numpy as np
	from numpy import array, arange, uint8 
	from matplotlib import pyplot as plt


	img = cv2.imread(&#39;lena_caption.png&#39;, cv2.IMREAD_COLOR)
	bw_img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

	images = []
	images.append(img)
	images.append(bw_img)

	titles = [&#39;Original Image&#39;,&#39;BW Image&#39;]
	 
	for i in xrange(len(images)):
	    plt.subplot(1,2,i+1),plt.imshow(images[i],&#39;gray&#39;)
	    plt.title(titles[i])
	    plt.xticks([]),plt.yticks([])

	plt.show()


Here is the original image:
[![enter image description here][1]][1]

And here is the plotted image:
[![enter image description here][2]][2]


  [1]: http://i.stack.imgur.com/o9G7e.png
  [2]: http://i.stack.imgur.com/KagWq.png

OpenCV giving wrong color to colored images on loading

Is it possible to get the RGB color of a pixel using PIL?
I&#39;m using this code:

    im = Image.open(&quot;image.gif&quot;)
    pix = im.load()
    print(pix[1,1])

However, it only outputs a number (e.g. `0` or `1`) and not three numbers (e.g. `60,60,60` for R,G,B). I guess I&#39;m not understanding something about the function. I&#39;d love some explanation.

Thanks a lot.

Get pixel&#39;s RGB using PIL

What is the basic property of a linear RGB space and what is the fundamental property of a non-linear one? When talking about the values inside each channel in those 8 (or more) bits, what changes?

In OpenGL, colors are 3+1 values, and with this i mean RGB+alpha, with 8 bit reserved to each channel, and this is the part that i get clearly.

But when it comes to gamma correction i don&#39;t get what the effect of working in a non-linear RGB space is.

Since i know how to use a curve in a graphic software for photo-editing, my explanation is that in a linear RGB space you take the values as they are, with no manipulation and no math function attached, instead when it&#39;s non-linear each channel usually evolves following a classic power function behaviour.

Even if i take this explanation as the real one, i still don&#39;t get what a real linear space is, because after computation all non-linear RGB spaces becomes linear and most important of all i don&#39;t get the part where a non-linear color space is more suitable for the human eye because in the end all RGB spaces are linear for what i understand.

What are the practical differences when working with colors in a linear vs. a non-linear RGB space?

What would be a good way to convert hex color values like `#ffffff` into the single RGB values `255 255 255` using PHP?

Convert hex color to RGB values in PHP

I&#39;m creating a color object using the following code.

    curView.backgroundColor = [[UIColor alloc] initWithHue:229 saturation:40 brightness:75 alpha:1];

How can I retrieve RGB values from the created color object?

How to get RGB values from UIColor?

I&#39;m looking for some kind of formula or algorithm to determine the brightness of a color given the RGB values.  I know it can&#39;t be as simple as adding the RGB values together and having higher sums be brighter, but I&#39;m kind of at a loss as to where to start.

Formula to determine perceived brightness of RGB color

I&#39;m looking for an algorithm that compares two RGB colors and generates a value of their similarity (where similarity means &quot;similar with respect to average human perception&quot;).

Any ideas?


**EDIT**:

Since I cannot answer anymore I decided to put my &quot;solution&quot; as an edit to the question.

I decided to go with a (very) small subset of true-color in my app, so that I can handle comparison of colors by my own. I work with about 30 colors and use hard-coded distances between them.

Since it was an iPhone app I worked with objective-C and the implementation is more or less a matrix representing the table below, which shows the distances between the colors.

![enter image description here][1] 


  [1]: http://i.stack.imgur.com/bnNPt.png

Algorithm to check similarity of colors

How to convert a RGBA color tuple, example (96, 96, 96, 202), to corresponding RGB color tuple?

&lt;strong&gt;Edit:&lt;/strong&gt;

What I want is to get a RGB value which is most similar to the RGBA tuple visually on white background.

Convert RGBA color to RGB

How can I convert a RGB Color to HSV using C#?&lt;br/&gt;
I&#39;ve searched for a fast method without using any external library.

How to Convert RGB Color to HSV?

`rgb(255,255,255)` notation has been available since CSS1. But `#ffffff` seems to be vastly more popular.

Obviously it&#39;s slightly more compact. I know that hex is more closely related to the underlying bytes, and understand that there would be advantages in carrying out arithmetic on those values, but this isn&#39;t something you&#39;re going to do with CSS.

Colour values tend to be originated by designers (such as myself) who would never encounter hex notation anywhere else, and are much more familiar with the decimal notation which is the main way of specifying colour in the apps they use -- in fact I have met quite a few who don&#39;t realise how a given hex value breaks down into RGB components and assumed it didn&#39;t directly relate to the colour at all, like a Pantone colour system reference (eg PMS432).

So, any reason not to use decimal?

Are there any good reasons for using hex over decimal for RGB colour values in CSS?

Does anybody know, off the top of your heads, a Javascript solution for calculating the complementary colour of a hex value?

There are a number of colour picking suites and palette generators on the web but I haven&#39;t seen any that actually calculate the colour dynamically using JS.

A detailed hint or a snippet would be very much appreciated.

JS function to calculate complementary colour?

I want to display a color based on a value from 0 to 100. At one end (100), it&#39;s pure Red, the other end (0), pure Green. In the middle (50), I want it to be yellow.

And I want the colors to fade gradually from one to another, such that at 75, the color is half red and half yellow, etc.

How do I program the RGB values to reflect this fading? Thanks.

Algorithm: How do I fade from Red to Green via Yellow using RGB values?

How can I get the RGB value of a particular pixel in a UIImage?

Get Pixel color of UIImage

## Overview

I have an image buffer that I need to convert to another format.  The origin image buffer is four channels, 8 bits per channel, Alpha, Red, Green, and Blue.  The destination buffer is three channels, 8 bits per channel, Blue, Green, and Red.

So the brute force method is:

    // Assume a 32 x 32 pixel image
    #define IMAGESIZE (32*32)

    typedef struct{ UInt8 Alpha; UInt8 Red; UInt8 Green; UInt8 Blue; } ARGB;
    typedef struct{ UInt8 Blue; UInt8 Green; UInt8 Red; } BGR;

    ARGB orig[IMAGESIZE];
    BGR  dest[IMAGESIZE];

    for(x = 0; x &lt; IMAGESIZE; x++)
    {
         dest[x].Red = orig[x].Red;
         dest[x].Green = orig[x].Green;
         dest[x].Blue = orig[x].Blue;
    }

However, I need more speed than is provided by a loop and three byte copies. I&#39;m hoping there might be a few tricks I can use to reduce the number of memory reads and writes, given that I&#39;m running on a 32 bit machine.

## Additional info

Every image is a multiple of at least 4 pixels.  So we could address 16 ARGB bytes and move them into 12 RGB bytes per loop. Perhaps this fact can be used to speed things up, especially as it falls nicely into 32 bit boundaries.

I have access to OpenCL - and while that requires moving the entire buffer into the GPU memory, then moving the result back out, the fact that OpenCL can work on many portions of the image simultaneously, and the fact that large memory block moves are actually quite efficient may make this a worthwhile exploration.

While I&#39;ve given the example of small buffers above, I really am moving HD video (1920x1080) and sometimes larger, mostly smaller, buffers around, so while a 32x32 situation may be trivial, copying 8.3MB of image data byte by byte is really, really bad.

Running on Intel processors (Core 2 and above) and thus there are streaming and data processing commands I&#39;m aware exist, but don&#39;t know about - perhaps pointers on where to look for specialized data handling instructions would be good.

This is going into an OS X application, and I&#39;m using XCode 4.  If assembly is painless and the obvious way to go, I&#39;m fine traveling down that path, but not having done it on this setup before makes me wary of sinking too much time into it.

Pseudo-code is fine - I&#39;m not looking for a complete solution, just the algorithm and an explanation of any trickery that might not be immediately clear.

Fast method to copy memory with translation - ARGB to BGR

I am working on an iPhone application which uses various colors. When user selects the particular color button I set drawing color accordingly. I am getting the color for some but in the most of the cases I am getting white color.

Here is my code:
          
    -(IBAction)colorSelected:(UIButton *)sender
    {

    switch (sender.tag) 
    {
        case 1:
            self.drawcolor= [UIColor colorWithRed:200 green:191 blue:231 alpha:1];
            break;            
        case 2:
            self.drawcolor= [UIColor colorWithRed:163 green:73 blue:164 alpha:1];
            break;  
        case 3:
            self.drawcolor= [UIColor colorWithRed:112 green:146 blue:76 alpha:1];
            break;  
        case 4:
            self.drawcolor= [UIColor colorWithRed:63 green:72 blue:204 alpha:1];
            break;  
        case 5:
            self.drawcolor= [UIColor colorWithRed:153 green:217 blue:234 alpha:1];
            break;  
        case 6:
            self.drawcolor= [UIColor colorWithRed:0 green:162 blue:232 alpha:1];
            break;          
        case 7:
            self.drawcolor= [UIColor colorWithRed:181 green:230 blue:29 alpha:1];
            break;  
        case 8:
            self.drawcolor= [UIColor colorWithRed:34 green:177 blue:76 alpha:1];
            break;          
        case 9:
            self.drawcolor= [UIColor colorWithRed:239 green:228 blue:176 alpha:1];
            break;          
        case 10:
            self.drawcolor= [UIColor colorWithRed:255 green:201 blue:0 alpha:1];
            break;          
        case 11:
            self.drawcolor= [UIColor colorWithRed:255 green:201 blue:14 alpha:1];
            break;          
        case 12:
            self.drawcolor= [UIColor colorWithRed:237 green:28 blue:36 alpha:1];
            break;          
        case 13:
            self.drawcolor= [UIColor colorWithRed:255 green:127 blue:39 alpha:1];
            break;          
        case 14:
            self.drawcolor= [UIColor colorWithRed:255 green:174 blue:201 alpha:1];
            break;          
        case 15:
            self.drawcolor= [UIColor colorWithRed:185 green:122 blue:87 alpha:1];
            break;          
        case 16:
            self.drawcolor= [UIColor colorWithRed:136 green:0 blue:21 alpha:1];
            break;          
        case 17:
            self.drawcolor= [UIColor colorWithRed:195 green:195 blue:195 alpha:1];
            break;          
        case 18:
            self.drawcolor= [UIColor colorWithRed:127 green:127 blue:127 alpha:1];
            break;          
        case 19:
            self.drawcolor= [UIColor colorWithRed:255 green:255 blue:255 alpha:1];
            break;
        case 20:
            self.drawcolor= [UIColor colorWithRed:0 green:0 blue:0 alpha:1];
            break;  
        default:
            break;
    }
    
    self.preColor=self.drawcolor;
    self.lineWidth=self.prelineWidth;
    }



Can any one tell me what I am doing wrong ?
Sumit

How to initialize UIColor from RGB values properly?

Using javascript with or without Jquery, I need to a create a gradient of colours based on a start and finish color. Is this possible to do programmatically?

The end colour is only ever going to be darker shade of the start colour and it&#39;s for an unordered list which I have no control over the number of li items. I&#39;m looking for a solution that allows me to pick a start and end color, convert the hex value into RGB so it can be manipulated in code. The starting RGB values gets incremented by a step value calculated based upon the number of items.

so if the list had 8 items then the it needs to increment the seperate Red Green Blue values in 8 steps to achieve the final colour. Is there a better way to do it and if so where can I find some sample code? 


Javascript color gradient

I am trying to change the color of the function swapFE() below and I can&#39;t figure out how to write it. I was told to change the color of the phrase node to the color value (155, 102, 102). I tried to do that as you can see at the end of the function see- parent.childNodes[1].style.color= (155, 102, 102); but it just comes out a dark navy blue. It&#39;s supposed to be a brownish red. I have no idea what I&#39;m doing wrong. How can I fix this to get the correct RGB color? I know I have the rest right it&#39;s just figuring out how to write the color and the value that&#39;s giving me problems. Thanks!

    //this function changes the French phrase to an English phrase. 
        function swapFE(e) { 
               var phrase = e.srcElement;  
               //phrase.innerText = english[phrase.id]; 
               var parent = phrase.parentNode; 
               //childNodes[0] is the number of the phrase +1  
               var idnum = parent.childNodes[0]; 
               //parseInt takes a textstring and extracts it to make a number. Then you will subtract 1 from the number. 
     
           var phrasenum = parseInt(idnum.innerHTML)-1; 
           phrase.innerText = english[phrasenum]; 
           parent.childNodes[1].style.fontStyle= &quot;normal&quot;; 
           parent.childNodes[1].style.color= (155, 102, 102); 
      } 
     
     
    function swapEF(e) { 
           var phrase = e.srcElement;  
           //phrase.innerText = english[phrase.id]; 
           var parent = phrase.parentNode; 
           var idnum = parent.childNodes[0]; 
           var phrasenum = parseInt(idnum.innerHTML)-1; 
           phrase.innerText = french[phrasenum]; 
           parent.childNodes[1].style.fontStyle= &quot;italic&quot;; 
           parent.childNodes[1].style.color= &quot;black&quot;; 



How do I write a RGB color value in JavaScript?

I am getting a UIColor returned from this method:

    - (UIColor *)getUserSelectedColor {   
        return [UIColor colorWithRed:redSlider.value green:greenSlider.value blue:blueSlider.value alpha:1.0];
    }

and getting color like this:

    UIColor *selectedColor = [(ColorPickerView *)alertView getUserSelectedColor];

Now I want to get red, green, blue from selectedColor, in order to use those values. I want values between 0 and 1.

All Rgb Solutions on Gang of Coders

Total of 36 Rgb Solutions