Get total number of the black and white pixels in bitmap image separately

Question

I am trying to write a code that goes through my image and counts all the pixels line by line and tells me how many white and how many black pixels are in my image? (Assuming my image is made of a black character against white background)

var backgroundPixels = 0;

     for (int x = 0; x < bmp.Width; x++)
            {
                for (int y = 0; y < bmp.Height; y++)
                {
                    if (bmp.GetPixel(x, y).Equals(Color.White))
                    {
                        backgroundPixels++;
                    }
                }

            }
            label3.Text = Convert.ToString(backgroundPixels);

I am having problem as the code doesn’t work for some reason. Can anyone help me please?

Answer 1

When you use == or Equals you are not comparing the value of ARGB byte by byte because the '==' operator is done like this

     public static bool operator ==(Color left, Color right)
        {
          if (left.value != right.value || (int) left.state != (int) right.state || (int) left.knownColor != (int) right.knownColor)
            return false;
          if (left.name == right.name)
            return true;
          if (left.name == null || right.name == null)
            return false;
          else
            return left.name.Equals(right.name);
        }

following is how is done the Equals Method in .net

public override bool Equals(object obj)
    {
      if (obj is Color)
      {
        Color color = (Color) obj;
        if (this.value == color.value && (int) this.state == (int) color.state && (int) this.knownColor == (int) color.knownColor)
        {
          if (this.name == color.name)
            return true;
          if (this.name == null || color.name == null)
            return false;
          else
            return this.name.Equals(this.name);
        }
      }
      return false;
    }

to overcome your issue you should convert to ARGB using the ToArgb() function which send 32-bit of the current color

 private void button1_Click(object sender, EventArgs e)
        {
            
            int whiteColor = 0;
            int blackColor = 0; 
            for (int x = 0; x < bmp.Width; x++)
            {
                for (int y = 0; y < bmp.Height; y++)
                {
                    Color color = bmp.GetPixel(x, y); 
                    
                    if (color.ToArgb()==Color.White.ToArgb())
                    {
                        whiteColor++;  
                    }

                    else
                        if (color.ToArgb() == Color.Black.ToArgb())
                        {
                            blackColor++; 
                        }
                }

            }
        }

Answer 2

It doesn't work because you are comparing Color structs:

if (bmp.GetPixel(x, y).Equals(Color.White))

the "Name" member of the struct is not going to be "White" on your pixel, it will be a string containing the hex value "ffffff", so the objects are different even though the ARGB values are the same. You need to compare the ARGB values. The Color struct is stupid like that.

if (bmp.GetPixel(x, y).ToArgb().Equals(Color.White.ToArgb()))

The other possibility is that your pixels aren't actually black and white but greyscale.