Number of colors in an Image

Hello,

I have a program that extracts the colors used in an image. The image is created by me using MSPaint (please take a look at the attached picture). I believe that the program should show atmost 7 unique colors. But i get many results. The code is given below:

import java.util.*;
import java.awt.Component;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;

public class ImageEx
		
{

Set<String> s = new HashSet<String>();
	
	ImageEx()
	{
		try {
		    BufferedImage image = ImageIO.read(this.getClass().getResource("circle.jpg"));
			fireOnImage(image);
			} catch (IOException e) {
			System.err.println(e.getMessage());
			}
	}
	
	public static void main(String args[])
	{
		new ImageEx();
	}
	
	private void fireOnImage(BufferedImage image) 
	{
		int w = image.getWidth();
		int h = image.getHeight();
		System.out.println("width, height: " + w + ", " + h);
		
		for (int i = 0; i < h; i++) {	
			for (int j = 0; j < w; j++) {
				//System.out.println("x,y: " + j + ", " + i);
				int pixel = image.getRGB(j, i);
				String pixs = Integer.toHexString(pixel);
				if(s.add(pixs))
					printPixelARGB(pixel);
				
			}
		}
	}
	
	public void printPixelARGB(int pixel) 
	{
		int alpha = (pixel >> 24) & 0xff;
		int red = (pixel >> 16) & 0xff;
		int green = (pixel >> 8) & 0xff;
		int blue = (pixel) & 0xff;
		System.out.println("argb: " + alpha + ", " + red + ", " + green + ", " + blue);
		System.out.println("argb: " + Integer.toHexString(pixel));
	}
	
}

Why does this happen?

You'll probably find that the extra colors occur around the circles perimeters. Most drawing programs don't just paint a single line of black pixels, they add interpolated pixels to the left and right of the line in order to create a smooth appearance.

So there'll probably be lots of colors that are halfway between black and whatever color happens to occur on one side of the line. I'm sure high-end drawing apps have a way of preventing this; not sure about Paint, though.