Screenshot conversion into grayscale doesn't work. What causes this?

Question

I have a Windows Forms application that takes a screenshot of a specific portion of the screen, then displays it in a picture box (pictureBox1). It works when I don't try to convert it, but I want to convert the image to grayscale or black and white. The problem is when I convert it to grayscale, it still shows the original picture in the picture box.

Here is the code when it works, without the conversion:

private void button1_Click(object sender, EventArgs e)
{
        Rectangle rectangle = new Rectangle(660, 200, 600, 100);
        pictureBox1.Height = rectangle.Height;
        pictureBox1.Width = rectangle.Width;

        imageUploader(rectangle);
}

public void imageUploader(Rectangle rectangle)
{
        Bitmap bitmap = new Bitmap(rectangle.Width, rectangle.Height, PixelFormat.Format32bppArgb);
        Graphics graphics = Graphics.FromImage(bitmap);
        graphics.CopyFromScreen(rectangle.Left, rectangle.Top, 0, 0, bitmap.Size, CopyPixelOperation.SourceCopy);

        bitmap.Save("proba.jpeg", ImageFormat.Jpeg);

        pictureBox1.Image = bitmap;
} 

Here is the conversion method, which I tried out:

public void toGrayscale(Bitmap bitmap)
    {
        Color c;

        for (int y = 0; y < bitmap.Height; y++)
        {
            for (int x = 0; x < bitmap.Width; x++)
            {
                c = bitmap.GetPixel(x,y);
                Color newColor = Color.FromArgb(c.R,0,0);
                bitmap.SetPixel(x,y,newColor);
            }
        }
    }

After I used this conversion (see below) the image showed up in the picture box, but it wasn't grayscale.

Here is the modified imageUploader void with the conversion:

    public void imageUploader(Rectangle rectangle)
    {
        Bitmap bitmap = new Bitmap(rectangle.Width, rectangle.Height, PixelFormat.Format32bppArgb);
        toGrayscale(bitmap);
        Graphics graphics = Graphics.FromImage(bitmap);
        graphics.CopyFromScreen(rectangle.Left, rectangle.Top, 0, 0, bitmap.Size, CopyPixelOperation.SourceCopy);

        bitmap.Save("proba.jpeg", ImageFormat.Jpeg);

        pictureBox1.Image = bitmap;
    } 

Answer 1

It appears that your issue is here:

    public void imageUploader(Rectangle rectangle)
    {
        Bitmap bitmap = new Bitmap(rectangle.Width, rectangle.Height, PixelFormat.Format32bppArgb);
        toGrayscale(bitmap);
        Graphics graphics = Graphics.FromImage(bitmap);
        graphics.CopyFromScreen(rectangle.Left, rectangle.Top, 0, 0, bitmap.Size, CopyPixelOperation.SourceCopy);

        bitmap.Save("proba.jpeg", ImageFormat.Jpeg);

        pictureBox1.Image = bitmap;
    }

You're converting each pixel of the bitmap to greyscale (oddly it looks like you're only grabbing the red channel) then copying from the screen, which overwrites your conversion. To fix it, all you should need to do is move the toGreyscale after you copy from the screen, like this:

    public void imageUploader(Rectangle rectangle)
    {
        Bitmap bitmap = new Bitmap(rectangle.Width, rectangle.Height, PixelFormat.Format32bppArgb);
        Graphics graphics = Graphics.FromImage(bitmap);
        graphics.CopyFromScreen(rectangle.Left, rectangle.Top, 0, 0, bitmap.Size, CopyPixelOperation.SourceCopy);
        toGrayscale(bitmap);  # Moved after the copy from screen
        bitmap.Save("proba.jpeg", ImageFormat.Jpeg);

        pictureBox1.Image = bitmap;
    }

This should fix the issue.