// The original image
Image<Bgr, float> image = new Image<Bgr, float>(@"C:image.jpg");

// Get the image width and height
int imageWidth = image.Width;

int imageHeight = image.Height;

// The ArcCos operated image
Image<Bgr, float> imageAcos = new Image<Bgr, float>(imageWidth, imageHeight);

// Start operating the image
for (int y = 0; y < imageHeight; y++)
{
    for(int x = 0; x < imageWidth; x++)
    {
    // The Blue frame
    imageAcos.Data[x, y, 0] = (float) Math.Acos((double) image.Data[x, y, 0]);

    // The Green frame
    imageAcos.Data[x, y, 1] = (float) Math.Acos((double) image.Data[x, y, 1]);

    // The Red frame
    imageAcos.Data[x, y, 2] = (float) Math.Acos((double) image.Data[x, y, 2]);
    }
}