问题
The task: I have some images, I scale them down, and join them to one image. But I have a little problem with the implementation:
The concrete problem: I want to resize/scale a BufferedImage. The getScaledInstance method returns an Image object, but I can't cast it to BufferedImage:
Exception in thread "main" java.lang.ClassCastException: sun.awt.image.ToolkitImage cannot be cast to java.awt.image.BufferedImage
(I don't know why is it a ToolkitImage instead of an Image...)
I found a solution:
Image tmp = bi.getScaledInstance(SMALL_SIZE, SMALL_SIZE, BufferedImage.SCALE_FAST);
BufferedImage buffered = new BufferedImage(SMALL_SIZE,SMALL_SIZE,BufferedImage.TYPE_INT_RGB);
buffered.getGraphics().drawImage(tmp, 0, 0, null);
But it's slow, and I think there should be a better way to do it.
I need the BufferedImage, because I have to get the pixels to join the small images.
Is there a better (nicer/faster) way to do it?
EDIT: If I cast the Image first to ToolkitImage, it has a getBufferedImage() method. But it always returns null. Do you know why?
回答1:
The Graphics object has a method to draw an Image while also performing a resize operation:
Graphics.drawImage(Image, int, int, int, int, ImageObserver) method can be used to specify the location along with the size of the image when drawing.
So, we could use a piece of code like this:
BufferedImage otherImage = // .. created somehow
BufferedImage newImage = new BufferedImage(SMALL_SIZE, SMALL_SIZE, BufferedImage.TYPE_INT_RGB);
Graphics g = newImage.createGraphics();
g.drawImage(otherImage, 0, 0, SMALL_SIZE, SMALL_SIZE, null);
g.dispose();
This will take otherImage and draw it on the newImage with the width and height of SMALL_SIZE.
Or, if you don't mind using a library, Thumbnailator could accomplish the same with this:
BufferedImage newImage = Thumbnails.of(otherImage)
.size(SMALL_SIZE, SMALL_SIZE)
.asBufferedImage();
Thumbnailator will also perform the resize operation quicker than using Image.getScaledInstance while also performing higher quality resize operations than using only Graphics.drawImage.
Disclaimer: I am the maintainer of the Thumbnailator library.
回答2:
I get it with this method, it resizes the Image and tries to maintain the proportions:
/**
* Resizes an image using a Graphics2D object backed by a BufferedImage.
* @param srcImg - source image to scale
* @param w - desired width
* @param h - desired height
* @return - the new resized image
*/
private BufferedImage getScaledImage(BufferedImage src, int w, int h){
int finalw = w;
int finalh = h;
double factor = 1.0d;
if(src.getWidth() > src.getHeight()){
factor = ((double)src.getHeight()/(double)src.getWidth());
finalh = (int)(finalw * factor);
}else{
factor = ((double)src.getWidth()/(double)src.getHeight());
finalw = (int)(finalh * factor);
}
BufferedImage resizedImg = new BufferedImage(finalw, finalh, BufferedImage.TRANSLUCENT);
Graphics2D g2 = resizedImg.createGraphics();
g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
g2.drawImage(src, 0, 0, finalw, finalh, null);
g2.dispose();
return resizedImg;
}
回答3:
You can also use OpenCV Java library. It's resize operation is faster than Imgscalr's:
Test
Image 5184 x 3456 scaled to 150 x 100 (this is the smaller version because original file is bigger than 2mb):
Imgscalr
Dependency:
<dependency>
<groupId>org.imgscalr</groupId>
<artifactId>imgscalr-lib</artifactId>
<version>4.2</version>
</dependency>
Code:
BufferedImage thumbnail = Scalr.resize(img,
Scalr.Method.SPEED,
Scalr.Mode.AUTOMATIC,
150,
100);
Result image:
Average time: 80 millis
OpenCV
Dependency:
<dependency>
<groupId>nu.pattern</groupId>
<artifactId>opencv</artifactId>
<version>2.4.9-4</version>
</dependency>
Convert BufferedImage to Mat object (have to):
BufferedImage img = ImageIO.read(image); // load image
byte[] pixels = ((DataBufferByte) img.getRaster().getDataBuffer())
.getData();
Mat matImg = new Mat(img.getHeight(), img.getWidth(), CvType.CV_8UC3);
matImg.put(0, 0, pixels);
Code:
Imgproc.resize(matImg, resizeimage, sz);
Additional configuration (for windows):
Add opencv_java249.dll to your JDK's bin directory.
Result image:
Average time: 13 millis
Overall Results
In the test just "resize" functions times are calculated. Imgscalr resized the given image in 80 milis where OpenCV done the same task in 13 millis. You can find the whole project below here to play around of it a little bit.
As you asked also easy way, if the performance of the Imgscalr library is good for you then it is deadly-easy. Because to use OpenCV as you see a library file must be located at your all development environments and servers. Also you have to use Mat objects.
Whole Project
Pom.xml:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.btasdemir</groupId>
<artifactId>testapp</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>testapp</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.imgscalr</groupId>
<artifactId>imgscalr-lib</artifactId>
<version>4.2</version>
</dependency>
<dependency>
<groupId>nu.pattern</groupId>
<artifactId>opencv</artifactId>
<version>2.4.9-4</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.bytedeco</groupId>
<artifactId>javacpp</artifactId>
<version>0.9</version>
</plugin>
</plugins>
</build>
</project>
App.java:
package com.btasdemir.testapp;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import org.imgscalr.Scalr;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.Size;
import org.opencv.highgui.Highgui;
import org.opencv.imgproc.Imgproc;
/**
* Hello world!
*
*/
public class App
{
public static void main( String[] args ) throws IOException
{
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
File image = new File("C:\\your_dir\\test.jpg");
BufferedImage img = ImageIO.read(image); // load image
long startTime = System.currentTimeMillis();//imgscalr------------------------------------------------------
//resize to 150 pixels max
BufferedImage thumbnail = Scalr.resize(img,
Scalr.Method.SPEED,
Scalr.Mode.AUTOMATIC,
150,
100);
// BufferedImage thumbnail = Scalr.resize(img,
// Scalr.Method.SPEED,
// Scalr.Mode.AUTOMATIC,
// 150,
// 100,
// Scalr.OP_ANTIALIAS);
System.out.println(calculateElapsedTime(startTime));//END-imgscalr------------------------------------------------------
File outputfile = new File("C:\\your_dir\\imgscalr_result.jpg");
ImageIO.write(thumbnail, "jpg", outputfile);
img = ImageIO.read(image); // load image
byte[] pixels = ((DataBufferByte) img.getRaster().getDataBuffer())
.getData();
Mat matImg = new Mat(img.getHeight(), img.getWidth(), CvType.CV_8UC3);
matImg.put(0, 0, pixels);
Mat resizeimage = new Mat();
Size sz = new Size(150, 100);
startTime = System.currentTimeMillis();//opencv------------------------------------------------------
Imgproc.resize(matImg, resizeimage, sz);
// Imgproc.resize(matImg, resizeimage, sz, 0.5, 0.5, Imgproc.INTER_CUBIC);
System.out.println(calculateElapsedTime(startTime));//END-opencv------------------------------------------------------
Highgui.imwrite("C:\\your_dir\\opencv_result.jpg", resizeimage);
}
protected static long calculateElapsedTime(long startTime) {
long stopTime = System.currentTimeMillis();
long elapsedTime = stopTime - startTime;
return elapsedTime;
}
}
回答4:
None of these answers were fast enough for me. So I finally programmed my own procedure.
static BufferedImage scale(BufferedImage src, int w, int h)
{
BufferedImage img = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
int x, y;
int ww = src.getWidth();
int hh = src.getHeight();
for (x = 0; x < w; x++) {
for (y = 0; y < h; y++) {
int col = src.getRGB(x * ww / w, y * hh / h);
img.setRGB(x, y, col);
}
}
return img;
}
回答5:
Using imgscalr – Java Image Scaling Library:
BufferedImage image = Scalr.resize(originalImage, Scalr.Method.BALANCED, newWidth, newHeight);
This is fast enough for me.
回答6:
Maybe this method will help:
public BufferedImage resizeImage(BufferedImage image, int width, int height) {
int type=0;
type = image.getType() == 0? BufferedImage.TYPE_INT_ARGB : image.getType();
BufferedImage resizedImage = new BufferedImage(width, height,type);
Graphics2D g = resizedImage.createGraphics();
g.drawImage(image, 0, 0, width, height, null);
g.dispose();
return resizedImage;
}
Don't forget those "import" lines:
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
And about casting:
The abstract class Imageis the superclass of all classes that represent graphical images.
We can't cast Image to BufferedImage because every BufferedImage is Image but vice versa is not true.
Image im = new BufferedImage(width, height, imageType);//this is true
BufferedImage img = new Image(){//.....}; //this is wrong
回答7:
public static double[] reduceQuality(int quality, int width, int height) {
if(quality >= 1 && quality <= 100) {
double[] dims = new double[2];
dims[0] = width * (quality/100.0);
dims[1] = height * (quality/100.0);
return dims;
} else if(quality > 100) {
return new double[] { width, height };
} else {
return new double[] { 1, 1 };
}
}
public static byte[] resizeImage(byte[] data, int width, int height) throws Exception {
BufferedImage bi = ImageIO.read(new ByteArrayInputStream(data));
BufferedImage bo = resizeImage(bi, width, height);
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ImageIO.write(bo, "jpg", bos);
bos.close();
return bos.toByteArray();
}
private static BufferedImage resizeImage(BufferedImage buf, int width, int height) {
final BufferedImage bufImage = new BufferedImage(width, height,
(buf.getTransparency() == Transparency.OPAQUE ? BufferedImage.TYPE_INT_RGB
: BufferedImage.TYPE_INT_ARGB));
final Graphics2D g2 = bufImage.createGraphics();
g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_NEAREST_NEIGHBOR);
g2.drawImage(buf, 0, 0, width, height, null);
g2.dispose();
return bufImage;
}
This is taken straight from imgscalr at https://github.com/rkalla/imgscalr/blob/master/src/main/java/org/imgscalr/Scalr.java
My average time reducing the quality of an image of 8mb with dimensions of 5152x3864 was ~800ms.
No dependencies. I hate them. Sometimes.
THIS WILL ONLY WORK WITH jpg IMAGES. As far as I'm concerned.
Example:
byte[] of = Files.readAllBytes(Paths.get("/home/user/Pictures/8mbsample.jpg"));
double[] wh = ImageUtil.reduceQuality(2, 6600, 4950);
long start = System.currentTimeMillis();
byte[] sof = ImageUtil.resizeImage(of, (int)wh[0], (int)wh[1]);
long end = System.currentTimeMillis();
if(!Files.exists(Paths.get("/home/user/Pictures/8mbsample_scaled.jpg"))) {
Files.createFile(Paths.get("/home/user/Pictures/8mbsample_scaled.jpg"), Util.getFullPermissions());
}
FileOutputStream fos = new FileOutputStream("/home/user/Pictures/8mbsample_scaled.jpg");
fos.write(sof); fos.close();
System.out.println("Process took: " + (end-start) + "ms");
Output:
Process took: 783ms
来源：https://stackoverflow.com/questions/16497853/scale-a-bufferedimage-the-fastest-and-easiest-way