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Add adaptive size writer with example, refs #551 
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‎README.md‎

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@@ -138,6 +138,7 @@ Below are the very pretty basic examples demonstrating of how Webcam Capture API
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* [How to flip (mirror) image displayed in ```WebcamPanel```](https://github.com/sarxos/webcam-capture/blob/master/webcam-capture/src/example/java/WebcamPanelFlippingExample.java)
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* [How to rotate image displayed in ```WebcamPanel```](https://github.com/sarxos/webcam-capture/blob/master/webcam-capture/src/example/java/WebcamPanelRotationExample.java)
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* [How to rotate image from camera with ```WebcamImageTransformer```](https://github.com/sarxos/webcam-capture/blob/master/webcam-capture/src/example/java/ImageTransformerRotationExample.java)
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* [How to use AdaptiveSizeWriter to compress images](https://github.com/sarxos/webcam-capture/blob/master/webcam-capture/src/example/java/AdaptiveSizeWriterExample.java)
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And here are some more advanced examples, few with quite fancy GUI.
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‎webcam-capture/src/example/java/AdaptiveSizeWriterExample.java‎

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import java.awt.BorderLayout;
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import java.awt.Dimension;
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import java.awt.Graphics;
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import java.awt.image.BufferedImage;
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import java.io.ByteArrayInputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import javax.imageio.ImageIO;
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import javax.swing.BorderFactory;
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import javax.swing.JFrame;
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import javax.swing.JPanel;
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import javax.swing.JSlider;
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import javax.swing.SwingUtilities;
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import javax.swing.event.ChangeEvent;
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import javax.swing.event.ChangeListener;
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import com.github.sarxos.webcam.Webcam;
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import com.github.sarxos.webcam.WebcamEvent;
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import com.github.sarxos.webcam.WebcamListener;
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import com.github.sarxos.webcam.WebcamResolution;
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import com.github.sarxos.webcam.util.AdaptiveSizeWriter;
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/**
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* This class demonstrate how you can use {@link AdaptiveSizeWriter} to compress video frame to JPEG
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* with a given max number of bytes.
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*/
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public class AdaptiveSizeWriterExample extends JFrame implements ChangeListener, WebcamListener {
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/**
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* Serial.
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*/
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private static final long serialVersionUID = 1L;
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/**
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* Lets assume we want to have our JPEG frames to have max size of 40 KiB.
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*/
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private static final int MAX_BYTES = 20 * 1024;
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/**
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* Lets assume we want to have our JPEG frames to have min size of 5 KiB.
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*/
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private static final int MIN_BYTES = 6 * 1024;
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/**
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* Webcam resolkution to use.
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*/
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private static final Dimension RESOLUTION = WebcamResolution.VGA.getSize();
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final JSlider slider = new JSlider(JSlider.VERTICAL, MIN_BYTES, MAX_BYTES, MIN_BYTES + (MAX_BYTES - MIN_BYTES) / 2);
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final Webcam webcam = Webcam.getDefault();
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final ImagePanel panel = new ImagePanel();
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final AdaptiveSizeWriter writer = new AdaptiveSizeWriter(slider.getValue());
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public AdaptiveSizeWriterExample() {
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slider.addChangeListener(this);
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slider.setMajorTickSpacing(2 * 1024);
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slider.setPaintTicks(true);
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slider.setPaintLabels(true);
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slider.setBorder(BorderFactory.createEmptyBorder(0, 0, 0, 10));
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panel.setPreferredSize(RESOLUTION);
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panel.setBorder(BorderFactory.createCompoundBorder(
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BorderFactory.createLoweredBevelBorder(),
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BorderFactory.createEmptyBorder(10, 10, 10, 10)));
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webcam.setViewSize(RESOLUTION);
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webcam.addWebcamListener(this);
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webcam.open(true);
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final JPanel root = new JPanel();
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root.setLayout(new BorderLayout());
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root.add(slider, BorderLayout.WEST);
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root.add(panel, BorderLayout.CENTER);
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root.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
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setContentPane(root);
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setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
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pack();
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setVisible(true);
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}
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@Override
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public void stateChanged(ChangeEvent e) {
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writer.setSize(slider.getValue());
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}
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@Override
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public void webcamOpen(WebcamEvent we) {
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}
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@Override
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public void webcamClosed(WebcamEvent we) {
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}
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@Override
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public void webcamDisposed(WebcamEvent we) {
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}
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@Override
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public void webcamImageObtained(WebcamEvent we) {
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panel.setImage(writer.write(we.getImage()));
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}
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public static void main(String[] args) throws IOException {
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new AdaptiveSizeWriterExample();
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}
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private class ImagePanel extends JPanel {
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private static final long serialVersionUID = 1L;
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private BufferedImage image;
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@Override
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protected void paintComponent(Graphics g) {
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g.drawImage(image, 0, 0, this);
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}
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public void setImage(byte[] bytes) {
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try (InputStream is = new ByteArrayInputStream(bytes)) {
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this.image = ImageIO.read(is);
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} catch (IOException e) {
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throw new IllegalStateException(e);
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}
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SwingUtilities.invokeLater(new Runnable() {
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@Override
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public void run() {
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repaint();
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}
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});
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}
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}
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}

‎webcam-capture/src/main/java/com/github/sarxos/webcam/util/AdaptiveSizeWriter.java‎

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package com.github.sarxos.webcam.util;
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import java.awt.image.BufferedImage;
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import java.io.ByteArrayOutputStream;
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import java.io.IOException;
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import javax.imageio.IIOImage;
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import javax.imageio.ImageIO;
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import javax.imageio.ImageWriteParam;
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import javax.imageio.ImageWriter;
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import javax.imageio.plugins.jpeg.JPEGImageWriteParam;
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import javax.imageio.stream.MemoryCacheImageOutputStream;
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/**
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* This class will save {@link BufferedImage} into a byte array and try to compress it a given size.
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*
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* @author Bartosz Firyn (sarxos)
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*/
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public class AdaptiveSizeWriter {
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private static final float INITIAL_QUALITY = 1f;
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private volatile int size;
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private final ByteArrayOutputStream baos = new ByteArrayOutputStream();
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private float quality = 1f; // 1f = 100% quality, at the beginning
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public AdaptiveSizeWriter(int size) {
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this.size = size;
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}
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public byte[] write(final BufferedImage bi) {
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// loop and try to compress until compressed image bytes array is not longer than a given
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// maximum value, reduce quality by 25% in every step
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int m = size;
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int s = 0;
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int i = 0;
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do {
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if ((s = compress(bi, quality)) > m) {
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quality *= 0.75;
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if (i++ >= 20) {
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break;
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}
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}
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} while (s > m);
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return baos.toByteArray();
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}
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/**
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* Compress {@link BufferedImage} with a given quality into byte array.
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*
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* @param bi the {@link BufferedImage} to compres into byte array
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* @param quality the compressed image quality (1 = 100%, 0.5 = 50%, 0.1 = 10%, etc)
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* @return The size of compressed data (number of bytes)
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*/
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private int compress(BufferedImage bi, float quality) {
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baos.reset();
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final JPEGImageWriteParam params = new JPEGImageWriteParam(null);
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params.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
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params.setCompressionQuality(quality);
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try (MemoryCacheImageOutputStream mcios = new MemoryCacheImageOutputStream(baos)) {
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final ImageWriter writer = ImageIO.getImageWritersByFormatName("jpg").next();
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writer.setOutput(mcios);
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writer.write(null, new IIOImage(bi, null, null), params);
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} catch (IOException e) {
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throw new IllegalStateException(e);
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}
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return baos.size();
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}
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public int getSize() {
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return size;
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}
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public void setSize(int size) {
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if (this.size != size) {
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this.size = size;
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this.quality = INITIAL_QUALITY;
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}
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}
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}

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