Image (colour) manipulation with ColorMatrix

Below is a code snippet derived from a few of the ideas in the article at Matrix Operations for Image Manipulation[^].

Whilst this code is C# it should be easily convertible to VB or Managed C++.

These three simple Methods make use of the ColorMatrix to achieve variations in the colour saturation.

This is the Method that does all the work.

private void ApplySaturation(float saturation)
{
    float rWeight = 0.3086f;
    float gWeight = 0.6094f;
    float bWeight = 0.0820f;

    float a = (1.0f - saturation) * rWeight + saturation;
    float b = (1.0f - saturation) * rWeight;
    float c = (1.0f - saturation) * rWeight;
    float d = (1.0f - saturation) * gWeight;
    float e = (1.0f - saturation) * gWeight + saturation;
    float f = (1.0f - saturation) * gWeight;
    float g = (1.0f - saturation) * bWeight;
    float h = (1.0f - saturation) * bWeight;
    float i = (1.0f - saturation) * bWeight + saturation;

    // Create a Graphics
    using (Graphics gr = this.CreateGraphics())
    {
        gr.Clear(this.BackColor);
        // Create a Bitmap
        using (Bitmap curBitmap = new Bitmap("roses.jpg"))
        {
            // ColorMatrix elements
            float[][] ptsArray = {
                                     new float[] {a,  b,  c,  0, 0},
                                     new float[] {d,  e,  f,  0, 0},
                                     new float[] {g,  h,  i,  0, 0},
                                     new float[] {0,  0,  0,  1, 0},
                                     new float[] {0, 0, 0, 0, 1}
                                 };
            // Create ColorMatrix
            ColorMatrix clrMatrix = new ColorMatrix(ptsArray);
            // Create ImageAttributes
            ImageAttributes imgAttribs = new ImageAttributes();
            // Set color matrix
            imgAttribs.SetColorMatrix(clrMatrix,
                ColorMatrixFlag.Default,
                ColorAdjustType.Default);
            // Draw Image with no effects
            gr.DrawImage(curBitmap, 0, 0, 200, 200);
            // Draw Image with image attributes
            gr.DrawImage(curBitmap,
                new Rectangle(205, 0, 200, 200),
                0, 0, curBitmap.Width, curBitmap.Height,
                GraphicsUnit.Pixel, imgAttribs);
        }
    }
}

This will convert an image to GreyScale. Use a saturation code of zero.

public void GreyScale()
{
    ApplySaturation(0.0f);
}

This will alter the saturation of an image. Use a code saturation of 0.5f.

public void Fade()
{
    ApplySaturation(0.5f);
}

This will give the complementary colours for an image. Use a saturation of -1.0f.

public void Complement()
{
    ApplySaturation(-1.0f);
}

Obviously you should substitute one of your own images for "roses.jpg", the more colourful the better.