Brightness

private int Clamp(int value)
{
    return Math.Max(0, Math.Min(255, value));
}
private Bitmap ApplyBrightnessFilter(Bitmap sourceImage, int brightness)
{
    Bitmap newImage = new Bitmap(sourceImage.Width, sourceImage.Height);

    for (int x = 0; x < sourceImage.Width; x++)
    {
        for (int y = 0; y < sourceImage.Height; y++)
        {
            Color pixel = sourceImage.GetPixel(x, y);

            int r = Clamp(pixel.R + brightness);
            int g = Clamp(pixel.G + brightness);
            int b = Clamp(pixel.B + brightness);

            Color newColor = Color.FromArgb(r, g, b);
            newImage.SetPixel(x, y, newColor);
        }
    }

    return newImage;
}