Thanks to @JonasH who pointed me in the right direction. The answer is indeed to simply multiply the matrices. Using this information, I was able to create this class which does exactly what I wanted:
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace BIUK9000
{
public class HSBTAdjuster
{
//Hue 0 - 360, 0 is no change
//Saturation 1 is no change, <1 for decrease, >1 for increase
//Brightness 1 is no change, <1 for decrease, >1 for increase
//Transparency 1 is fully opaque, <1 for transparency
public static Bitmap HSBTAdjustedBitmap(Bitmap bitmap, float hue, float saturation, float brightness, float transparency)
{
ImageAttributes imageAttributes = HSBTAdjustedImageAttributes(hue, saturation, brightness, transparency);
Bitmap result = new Bitmap(bitmap.Width, bitmap.Height);
using Graphics g = Graphics.FromImage(result);
g.DrawImage(bitmap,
new Rectangle(0,0, bitmap.Width, bitmap.Height),
0, 0, bitmap.Width, bitmap.Height,
GraphicsUnit.Pixel, imageAttributes);
return result;
}
public static ImageAttributes HSBTAdjustedImageAttributes(float hue, float saturation, float brightness, float transparency)
{
ImageAttributes ia = new ImageAttributes();
ia.SetColorMatrix(
MultipliedColorMatrix(
SBTShiftedColorMatrix(saturation, brightness, transparency),
HueRotatedColorMatrix(hue)),
ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
return ia;
}
private static ColorMatrix MultipliedColorMatrix(ColorMatrix sbtCm, ColorMatrix hCm)
{
ColorMatrix result = new ColorMatrix();
for (int i = 0; i < 5; i++)
{
for (int j = 0; j < 5; j++)
{
result[i, j] = sbtCm[i, 0] * hCm[0, j];
result[i, j] += sbtCm[i, 1] * hCm[1, j];
result[i, j] += sbtCm[i, 2] * hCm[2, j];
result[i, j] += sbtCm[i, 3] * hCm[3, j];
result[i, j] += sbtCm[i, 4] * hCm[4, j];
}
}
return result;
}
private static ColorMatrix SBTShiftedColorMatrix(float saturation, float brightness, float transparency)
{
//adapted from https://stackoverflow.com/a/14384449/9852011
// Luminance vector for linear RGB
const float rwgt = 0.3086f;
const float gwgt = 0.6094f;
const float bwgt = 0.0820f;
// Create a new color matrix
ColorMatrix colorMatrix = new ColorMatrix();
// Adjust saturation
float baseSat = 1.0f - saturation;
colorMatrix[0, 0] = baseSat * rwgt + saturation;
colorMatrix[0, 1] = baseSat * rwgt;
colorMatrix[0, 2] = baseSat * rwgt;
colorMatrix[1, 0] = baseSat * gwgt;
colorMatrix[1, 1] = baseSat * gwgt + saturation;
colorMatrix[1, 2] = baseSat * gwgt;
colorMatrix[2, 0] = baseSat * bwgt;
colorMatrix[2, 1] = baseSat * bwgt;
colorMatrix[2, 2] = baseSat * bwgt + saturation;
// Adjust brightness
float adjustedBrightness = brightness - 1f;
colorMatrix[4, 0] = adjustedBrightness;
colorMatrix[4, 1] = adjustedBrightness;
colorMatrix[4, 2] = adjustedBrightness;
colorMatrix[3, 3] = transparency;
return colorMatrix;
}
private static ColorMatrix HueRotatedColorMatrix(float hueShiftDegrees)
{
float theta = (float)(hueShiftDegrees / 360 * 2 * Math.PI); //Degrees --> Radians
float c = (float)Math.Cos(theta);
float s = (float)Math.Sin(theta);
float A00 = (float)(0.213 + 0.787 * c - 0.213 * s);
float A01 = (float)(0.213 - 0.213 * c + 0.413 * s);
float A02 = (float)(0.213 - 0.213 * c - 0.787 * s);
float A10 = (float)(0.715 - 0.715 * c - 0.715 * s);
float A11 = (float)(0.715 + 0.285 * c + 0.140 * s);
float A12 = (float)(0.715 - 0.715 * c + 0.715 * s);
float A20 = (float)(0.072 - 0.072 * c + 0.928 * s);
float A21 = (float)(0.072 - 0.072 * c - 0.283 * s);
float A22 = (float)(0.072 + 0.928 * c + 0.072 * s);
ColorMatrix cm = new ColorMatrix();
cm.Matrix00 = A00;
cm.Matrix01 = A01;
cm.Matrix02 = A02;
cm.Matrix10 = A10;
cm.Matrix11 = A11;
cm.Matrix12 = A12;
cm.Matrix20 = A20;
cm.Matrix21 = A21;
cm.Matrix22 = A22;
cm.Matrix44 = 1;
cm.Matrix33 = 1;
return cm;
}
}
}
The HSBTAdjustedBitmap method returns the bitmap passed into it with the hue, saturation, brightness and transparency adjusted by the passed arguments.
