imageB

Bitmap img;

"Imagen.ImageLocation = openFileDialog1.FileName.ToString();"
img = new Bitmap(openFileDialog1.FileName.ToString()); // Make a copy of the image in the Bitmap variable

Then go back to the design form and double click on the second button, this will lead you to the event, and then place the next code:

// First we declare the variable that will make the strig that will be printed in the textbox
string texto = "";
//The we make the cicles to read pixel by pixel and we make the comparation with the withe color.
for (int i = 0; i < img.Width; i++)
{
    for (int j = 0; j < img.Height; j++)
    {
        //When we add the value to the string we should invert the
        order because the images are reading from top to bottom
        //and the textBox is write from left to right.
        if (img.GetPixel(j, i).A.ToString() == "255" && img.GetPixel(j,
        i).B.ToString() == "255" && img.GetPixel(j, i).G.ToString() ==
        "255" && img.GetPixel(j, i).R.ToString() == "255")
        {
            texto = texto + "0";
        }
        else
        {
            texto = texto + "1";
        }
    }
    texto = texto + "\r\n"; // this is to make the enter between lines
}
//And finally we put the string to the textbox
txtArreglo.Text = texto;