JFrame loading question

I am taking a screenshot and running it through a filter to dim the image. I take this image and place it in a JLabel and show over a portion of the screen. When I do this, even though I use a MediaTracker, it shows a grey background for the JFrame for about .1s before the image is shown. I've trimmed out all the unnecessary code and I'm posting a compileable version below.

If I do not run the image through a filter, it displays instantly as it should. What could be causing this delay?

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.FilteredImageSource;
import java.awt.image.ImageFilter;
import java.awt.image.RGBImageFilter;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.LineBorder;

public class TestCase extends JPanel {
   
    /** Creates a new instance of TestCase */
    public TestCase() {    
        try{
            //take screenshot of selected area of screen
            Robot screenRobot = new Robot();  //temporary robot for acquiring screenshot
            Point captureOrigin = new Point(10,10);
            Dimension captureDimension = new Dimension(760, 600);
            Image fadedScreenImage = screenRobot.createScreenCapture(new Rectangle(captureOrigin, captureDimension));
           
            //decrease brightness of image                    
            ImageFilter dimFilter = new DimImageFilter();
            FilteredImageSource dimImageSrc = new FilteredImageSource(fadedScreenImage.getSource(), dimFilter);
            fadedScreenImage = Toolkit.getDefaultToolkit().createImage(dimImageSrc);
           
            //track loading of image
            MediaTracker mt = new MediaTracker(this);
            mt.addImage(fadedScreenImage, 1);

            //create undecorated JFrame and position it over portion of screen currently being captured
            JFrame fadedFrame = new JFrame();
            fadedFrame.setSize(captureDimension);
            fadedFrame.setUndecorated(true);
            fadedFrame.setLocation(captureOrigin.x-1, captureOrigin.y-1);
           
            //objects test code
            mt.waitForAll();
            System.out.println(mt.checkID(1));
            ImageIcon icon = new ImageIcon(fadedScreenImage);
            JLabel imagePanel = new JLabel(icon);
           
            //create image panel and position in in frame for display
//            ImagePanel imagePanel = new ImagePanel(fadedScreenImage, this);
            JPanel cp = new JPanel();
            cp.setLayout(new BorderLayout());
            cp.setBorder(new LineBorder(Color.GRAY, 1));
            fadedFrame.setContentPane(cp);
            cp.add(imagePanel);

            //reset cursor position to be center of capture area
            int xPos = (captureDimension.width/2) + captureOrigin.x;
            int yPos = (captureDimension.height/2) + captureOrigin.y;
            screenRobot.mouseMove(xPos, yPos);            
           
            //show simulated overlay
            fadedFrame.setVisible(true);
        }
        catch(Exception e) {
            //error handling code here - not yet implemented
            e.printStackTrace();
        }
       
    }

    public static void main(String[] args) {
        TestCase test = new TestCase();      
    }
   
    class DimImageFilter extends RGBImageFilter {
   
    /** Creates a new instance of PauseFilter */
    public DimImageFilter() {
        // work with pixels whose indices are into a color table
        canFilterIndexColorModel = true;
    }
   
    public int filterRGB(int x, int y, int rgb) {
           
        // find out the red, green and blue color components
        int r = (rgb >> 16) & 0xff;
        int g = (rgb >> 8)  & 0xff;
        int b = (rgb)       & 0xff;

        //calculate the muted colors
        r = (r * 90)/100;
        g = (g * 90)/100;
        b = (b * 90)/100;

        return (rgb & 0xff000000) | (r<<16) | (g<<8) | (b);

    }
   
}
   
}

Thanks,
David