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LMS color space

LMS

  • Type: LMSColor
  • Channels:
    • L (long) usually between 0 and 1
    • M (medium) usually between 0 and 1
    • S (short) usually between 0 and 1

The LMS color space is designed to represent the response of three types of cones in the human eye:

  • Long cones (L) that respond to long wavelengths (red light).
  • Medium cones (M) that respond to medium wavelengths (green light).
  • Short cones (S) that respond to short wavelengths (blue light).

LMS is used in Colourful to perform chromatic adaptation either during conversion between color spaces that use different white points, or alternatively to white-balance a color.

// red
var c1 = new LMSColor(0.3823, 0.0811, 0.07162);

// white (D65)
var c2 = new LMSColor(0.9414, 1.0404, 1.0895);

// gray (D65)
var c3 = new LMSColor(0.2015, 0.2227, 0.2332);

// black
var c4 = new LMSColor(0, 0, 0);

Conversion strategy

When we convert from LMSColor to any other color space, the conversion always goes through the XYZ color space. The LMSColor can also appear in the conversion process as chromatic adaptation is performed in this color space.

The ConverterBuilder class can be set up with different LMS transformation matrices that correspond to different methods of chromatic adaptation. See more at LMS transformation matrix.

How to convert between LMS and RGB?

In this example, the conversion from RGB color space to LMS is demonstrated. We use the sRGB working space and keep the D65 white point.

var inputRgb = new RGBColor(0.937, 0.2, 0.251);
var rgbWorkingSpace = RGBWorkingSpaces.sRGB;

var rgbToLms = new ConverterBuilder().FromRGB(rgbWorkingSpace).ToLMS(rgbWorkingSpace.WhitePoint).Build();
var outputLms = rgbToLms.Convert(inputRgb); // LMS [L=0.38, M=0.08, S=0.07]

The reverse is similar:

var inputLms = new LMSColor(0.3823, 0.0811, 0.07162);
var rgbWorkingSpace = RGBWorkingSpaces.sRGB;

var lmsToRgb = new ConverterBuilder().FromLMS(rgbWorkingSpace.WhitePoint).ToRGB(rgbWorkingSpace).Build();
var outputRgb = lmsToRgb.Convert(inputLms); // RGB [R=0.94, G=0.2, B=0.25]

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