Find the nearest color with C# - Using the Euclidean distance between two colors

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Description

This small method provides an algorithm to find the nearest (or "most similar") color in a given "colorspace" compared to a given single color. This is done by searching for the least Euclidean distance between the two colors. The Euclidean distance can be computed in an arbitrary n-dimensional space. In this implementation, the value for the alpha-component of the given color to "approximate" is NOT used. In the sample I have used a little bit code written by Julijan Sribar (http://www.codeproject.com/cs/miscctrl/MultiTabColorPicker.asp) to receive the "web colors" as the sample color space. The webcolor-space is actually a subspace of the RGB-space.

The Algorithm

It is quite simple to compute the Euclidean distance between two points. First, convert the three color-components to double-values:

double dbl_input_red = Convert.ToDouble(input_color.R);
double dbl_input_green = Convert.ToDouble(input_color.G);
double dbl_input_blue = Convert.ToDouble(input_color.B);

Further define a "similarity measure" (actually this is THE distance). This measure has to be initialized by an arbitrary value which must be greater than the greatest possible distance (basically this is the distance between white and black).

double distance = 500.0;

The algorithm to find the least distance is quite simple:

Color nearest_color = Color.Empty;
foreach (object o in WebColors)
{
	// compute the Euclidean distance between the two colors
	// note, that the alpha-component is not used in this example
	dbl_test_red = Math.Pow(Convert.ToDouble(((Color)o).R) - dbl_input_red, 2.0);
	dbl_test_green = Math.Pow(Convert.ToDouble(((Color)o).G) - dbl_input_green, 2.0);
	dbl_test_blue = Math.Pow(Convert.ToDouble(((Color)o).B) - dbl_input_blue, 2.0);
	// it is not necessary to compute the square root
	// it should be sufficient to use:
	// temp = dbl_test_blue + dbl_test_green + dbl_test_red;
	// if you plan to do so, the distance should be initialized by 250000.0
	temp = Math.Sqrt(dbl_test_blue + dbl_test_green + dbl_test_red);
	// explore the result and store the nearest color
	if(temp == 0.0)
	{
		// the lowest possible distance is - of course - zero
		// so I can break the loop (thanks to Willie Deutschmann)
		// here I could return the input_color itself
		// but in this example I am using a list with named colors
		// and I want to return the Name-property too
		nearest_color = (Color)o;
		break;
	}
	else if (temp < distance)
	{
		distance = temp;
		nearest_color = (Color)o;
	}
}

Use

To use the code, simply copy and paste the method GetNearestWebColor(Color input_color) into your project. Alternatively you can place a reference to SampleLibrary.dll.

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Hope it solves a problem coleydog 23:00 6 May '08   The things one does. Where does it lead. I'd bet you'd never guess... My problem is with Citrix and client PC color depth. The Citrix clients run at 8-bit color versus my development laptop at 32-bit color. The problem is that it is almost impossible to find a back color for a control that doesn't appear 'hashed' (making the text almost unreadable) under 8-bit screen color on a Citrix client. I am hoping that the list of web colors will reflect the actual colors that work in 8-bit depth on the Citrix client. I'll let you know. Sign In·View Thread·PermaLink Two small suggestions. Willi Deutschmann 5:13 8 Jan '07   Hi, If I may make two suggestions which could speed up your code just a little. 1. If you ever encounter a distance of "0", you can break the loop and return that very color - you won't get any closer than that... 2. You don't need to calculate the square root. It is of course the mathematically correct way for distances, but you are merely finding a minimum value, i.e. you are comparing only those numbers among each other and not to a specific reference distance. Additionally - but I am not 100% sure - you could try replacing the "Math.Pow" by a simple "Math.Abs". Seven days without coffee makes one weak. Sign In·View Thread·PermaLink Re: Two small suggestions. _vt_ 7:28 8 Jan '07   Hi! Thank you for your suggestions. I will implement the first one soon. The second one ... well I will think about it. I love Euclidean geometry and so it is quite hard to make a decision... Thanks! ************************* Do, ut des. Sign In·View Thread·PermaLink No one uses euclidian distance Gilad Kapelushnik 0:28 7 Jan '07   A couple of years ago LAB was the favorite methods for most of the market, today there are better standars, Sign In·View Thread·PermaLink 2.00/5 (1 vote) Re: No one uses euclidian distance _vt_ 1:51 7 Jan '07   Thank you for your comment. Well - this is my first attempt to contribute some minor/usefull code to the community. I think this approach is usefull - particularly for "fun programmers". Of course - there are a lot of algorithms able to handle this problem. Maybe I will post a more sophisticated solution. Do, ut des. Sign In·View Thread·PermaLink Re: No one uses euclidian distance JohnnyLocust 10:55 20 Sep '07   Euclidean distance is used quite often in shader languages such as HLSL and GLSL. Sign In·View Thread·PermaLink

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