CS 335 Graphics and Multimedia

Image Manipulation

Image ManipulationIndependent pixels:

image subtractionimage averaginggrey level mappingthresholding

Neighborhoods of pixels:filtering, convolution, etc.

Geometric operations on pixels:rotation, scale, warp

Manipulating Images in Java

Image class:provides simple file/network readdifficult to access individual pixelseasy to make into an icon

BufferedImage class:simple file/network readeasy access to pixelscan get graphics context

Treating Pixels Independently

Image Arithmetic:Change the values of pixels based on a rule which uses information from that pixel onlyAddition/averaging: average multiple images over timeSubtraction: detect changes over timeNegative: invert the color map

Image Addition

Image Subtraction

Image Subtraction

Pixel-wise Logical Operations

AND XOR OR

Grey Level Mapping

Remap the intensity distribution of pixelsEnhances contrast between features and structures

Original image grey levels

Target imagegrey levels

Grey Level Mapping

Mapping curve can be arbitraryExample: first interval is compressed, second interval is stretched

Original image grey levels

Target imagegrey levels

Grey Level Mapping

Example: monotonically increasing curve (not line)

Original image grey levels

Target imagegrey levels

Grey Level Mapping

Example: non-monotonically increasing curve

Original image grey levels

Target imagegrey levels

Thresholding

Pixel modification based on a specified threshold criterion:

<

=otherwisey

threshold oldpixel ifx newvalue

Goal: suppress values below threshold, enhance values above

Image Histograms

Histogram: frequency distribution of grey levels or colors in that imageCan be a strong indicator for enhancement schemes: contrast enhancement, thresholdingHistograms are not unique: many images can produce the same histogramHistogram equalization: enhancement based on the histogram

Frequency Distribution

Horizontal axis: grey level valueVertical axis: count

0 255

512x512

The Normalized Histogram

Divide each “bin” by the total pixel countBin total becomes normalized to 1

Modifying the Histogram

Grey level modification will affect the histogram:

0 255 0 255

Using the Histogram for Thresholding

Threshold value can be calculated from the shape of the histogram:

0 255

Localized Histograms

Can compute histogram for a Region of Interest (ROI)Compute total number of pixels in ROICompute pixel intensity distribution within ROICan apply enhancements more locally

Histogram Equalization (Flattening)Evenly distribute intensity values across dynamic rangeResulting histogram is flatCan be a complex grey level mapping: is usually easier to specify as a histogram operation

Original Image Histogram-equalized Image

Intensity map to accomplishthe flattening operation

Examples

Examples

“Photo of the Year” 2002

Take-home Exercises

Ex 6.7: 1, 3, pp 132, Efford

/************************************************************

Sample: Program to load a JPEG image and display it in a JFRAME

************************************************************/

import java.awt.*;import java.awt.event.*;import java.awt.image.*;import java.io.*;import javax.swing.*;import javax.swing.event.*;import com.sun.image.codec.jpeg.*;

public class MyImageViewer extends JFrame {

// Instance variablesprivate BufferedImage image; // the imageprivate MyImageObj view; // a component for displayprivate JLabel infoLabel; // a label for the GUIprivate int x, y;private boolean firstdrag=true;

// The Constructor for this extension of the JFrame classpublic MyImageViewer (String filename) throws IOException {

super(filename);

// Load an image from a fileimage = readImage(filename);

// Create components to display image and pixel informationview = new MyImageObj(image);infoLabel = new JLabel();

infoLabel.addMouseListener(new MouseAdapter() {

public void mousePressed (MouseEvent event) {view.repaint();

}}

);

// Listen for mouse events to show (x,y) coordinates on infoLabelview.addMouseMotionListener(

new MouseMotionAdapter() {public void mouseMoved(MouseEvent event) {

infoLabel.setText((event.getPoint()).toString());}public void mouseDragged(MouseEvent event) {

Graphics g = view.getImage().getGraphics();g.setColor (Color.white);if (firstdrag) {

x = event.getX(); y = event.getY();firstdrag = false;

}else {g.drawLine (x, y, x=event.getX(),y=event.getY());

}view.repaint();

}}

);view.addMouseListener(

new MouseAdapter() {public void mouseReleased(MouseEvent event) {

firstdrag = true;}

});

// Build the JPanel which holds (for now) the infoLabelJPanel controlPane = new JPanel();controlPane.add(infoLabel);

// Add the JPanel and the image data component to the JFramegetContentPane().add(view, BorderLayout.CENTER);getContentPane().add(controlPane, BorderLayout.SOUTH);

}

public BufferedImage readImage (String file) throws IOException {

try {FileInputStream fin = new FileInputStream(file);JPEGImageDecoder decoder =

JPEGCodec.createJPEGDecoder(fin);image = decoder.decodeAsBufferedImage();fin.close();

}catch (IOException e) {}return image;

}

public static void main(String[] argv) {

// look for a command-line filenameif (argv.length > 0) {

try {JFrame frame = new MyImageViewer(argv[0]);frame.pack();frame.setVisible(true);frame.addWindowListener (

new WindowAdapter () {public void windowClosing ( WindowEvent e) {

System.exit(0);}

});

}catch (Exception e) {

System.err.println(e);System.exit(1);

}}// no command-line filename was providedelse {

System.err.println("usage: java MyImageViewer <imagefile>");System.exit(1);

}}

/*****************************************************************This is a helper object (could be described its own file) thatextends JLabel so that it can hold a BufferedImage

**************************************************************/

public class MyImageObj extends JLabel {

// instance variable to hold the buffered imageprivate BufferedImage image;

public MyImageObj(BufferedImage img) {setImage(img);setPreferredSize(new Dimension(image.getWidth(),

image.getHeight()));}

public void setImage(BufferedImage img) {image = img;

}

public BufferedImage getImage() {return image;

}

public void paintComponent(Graphics g) {g.drawImage(image, 0, 0, this);

}}}