How to convert an image from RGB to YIQ using c#?

Question

C++ / C#

I tried to convert. Here is my code:

private void RGBtoYIQbutton_Click(object sender, EventArgs e)
        {
            int[] vector_yiq = new int[3];
            double r, g, b, y, i, q;

            Bitmap bmp = new Bitmap(pictureBox1.Image);

            for (int x = 0; x < bmp.Width; x++)
            {
                for (int y = 0; y < bmp.Height; y++)
                {
                    Color clr = bmp.GetPixel(x, y);
                    r = (double)clr.R / 255;
                    g = (double)clr.G / 255;
                    b = (double)clr.B / 255;

                    y = Convert.ToInt32((0.299 * r + 0.587 * g + 0.114 * b) * 100);
                    i = Convert.ToInt32((0.596 * r - 0.274 * g - 0.322 * b) * 100);
                    if (i < 0)
                        i = Convert.ToInt32((0.596 * r - 0.274 * g - 0.322 * b + 0.5957) * 100);
                    q = Convert.ToInt32((0.211 * r - 0.522 * g + 0.311 * b ) * 100);
                    if (q < 0)
                        q = Convert.ToInt32((0.211 * r - 0.522 * g + 0.311 * b + 0.5226) * 100);

                    Color pixelColor;
                    pixelColor = Color.FromArgb(y, i, q);
                    bmp.SetPixel(x, y, pixelColor);
                }
            }
            pictureBox1.Image = bmp;
}

I know that the Y parameter has a range of [0,1], the I parameter has a range of [-0.523,0.523], and the Q parameter has a range of [-0.596,0.596]. Also I know that R, G and B have a range of [0,255].
You need to somehow bring the ranges or I don’t understand something. I'm using "if" to get positive values ​​for G and B. Because of this, I'm getting the wrong image. How can I make this transfer?
And in general, is it possible to set the color of a pixel somehow differently?

Answer 1

pixelColor = Color.FromArgb(y, i, q);
as you rightly pointed out on stackoverfow , you only need to use this method for RGB/RGBA. It does not know how to work directly with yiq .NET. Usually non-standard color spaces are used for intermediate transformations.
By the way, parameter i has range [-0.522, 0.522] and i [-0.596, 0.596].
In the course of the algorithm, you don’t need these ifs either, the coefficients do everything for you. For example:
i = 0.596 * r - 0.274 * g - 0.322 * b;
i = 0.596 * 0 - 0.274 * 1 - 0.322 * 1;
i = -0.596
hence you do not need any of these perversions with ifs.
p.s. Why are you multiplying by 100? Are you trying to adjust the values ​​in such a way that FromArgb would eat them? You don't need to do this.
And what's the point if changing the color space doesn't change your color...