ColorMatrixEffect uses a Matrix5x4 to modify the colors of an image. It can be configured to produce a wide range of color manipulation effects such as brightness or contrast adjustment, desaturation, sepia tinting, hue rotation, and swapping or inverting color channels.

Mathematical explanation: an (r,g,b,a) color value can be interpreted as a 4 dimensional vector. This vector is extended to 5 dimensions as (r,g,b,a,1). The 5d vector is multiplied by a 5x4 matrix, then the 5th component of the result is discarded, producing an (r,g,b,a) result.

Practical explanation: each component of the output color is a weighted average of all the input components. The transform matrix specifies what weights to use (which may be fractional, arbitrarily large, or negative):

• result.R = (src.R * matrix.M11) + (src.G * matrix.M21) + (src.B * matrix.M31) + (src.A * matrix.M41) + matrix.M51
• result.G = (src.R * matrix.M12) + (src.G * matrix.M22) + (src.B * matrix.M32) + (src.A * matrix.M42) + matrix.M52
• result.B = (src.R * matrix.M13) + (src.G * matrix.M23) + (src.B * matrix.M33) + (src.A * matrix.M43) + matrix.M53
• result.A = (src.R * matrix.M14) + (src.G * matrix.M24) + (src.B * matrix.M34) + (src.A * matrix.M44) + matrix.M54

The identity matrix is a simple no-op transform which passes color values through unchanged:

var identity = new Matrix5x4
{ 
    M11 = 1, M12 = 0, M13 = 0, M14 = 0,
    M21 = 0, M22 = 1, M23 = 0, M24 = 0,
    M31 = 0, M32 = 0, M33 = 1, M34 = 0,
    M41 = 0, M42 = 0, M43 = 0, M44 = 1,
    M51 = 0, M52 = 0, M53 = 0, M54 = 0
};

This matrix swaps the red and blue color channels:

var swapRedAndBlue = new Matrix5x4
{ 
    M11 = 0, M12 = 0, M13 = 1, M14 = 0,
    M21 = 0, M22 = 1, M23 = 0, M24 = 0,
    M31 = 1, M32 = 0, M33 = 0, M34 = 0,
    M41 = 0, M42 = 0, M43 = 0, M44 = 1,
    M51 = 0, M52 = 0, M53 = 0, M54 = 0
};

This matrix separately adjusts the brightness of each color channel:

var adjustBrightness = new Matrix5x4
{ 
    M11 = redAmount, M12 = 0,           M13 = 0,          M14 = 0,
    M21 = 0,         M22 = greenAmount, M23 = 0,          M24 = 0,
    M31 = 0,         M32 = 0,           M33 = blueAmount, M34 = 0,
    M41 = 0,         M42 = 0,           M43 = 0,          M44 = 1,
    M51 = 0,         M52 = 0,           M53 = 0,          M54 = 0
};

This matrix desaturates the image, converting colors to monochrome:

var desaturate = new Matrix5x4
{ 
    M11 = 0.333f, M12 = 0.333f, M13 = 0.333f, M14 = 0,
    M21 = 0.333f, M22 = 0.333f, M23 = 0.333f, M24 = 0,
    M31 = 0.333f, M32 = 0.333f, M33 = 0.333f, M34 = 0,
    M41 = 0,      M42 = 0,      M43 = 0,      M44 = 1,
    M51 = 0,      M52 = 0,      M53 = 0,      M54 = 0
};

This matrix copies the luminance (brightness) of the RGB color into the alpha channel, and sets RGB to a constant white:

var luminanceToAlpha = new Matrix5x4
{ 
    M11 = 0, M12 = 0, M13 = 0, M14 = 0.333f,
    M21 = 0, M22 = 0, M23 = 0, M24 = 0.333f,
    M31 = 0, M32 = 0, M33 = 0, M34 = 0.333f,
    M41 = 0, M42 = 0, M43 = 0, M44 = 0,
    M51 = 1, M52 = 1, M53 = 1, M54 = 0
};

This Windows Runtime type corresponds to the D2D Color matrix effect.

Reference