我有一个应用程序,我需要选择一个包含图片的文件夹,并需要使用Java显示这些图像的缩略图。我不知道如何用缩略图格式表示图像。
代码示例,理论或链接等任何资源都非常有用。
谢谢
答案 0 :(得分:1)
我在我的一个项目中使用了这段代码。我刚才在网上找到了(不知道在哪里,但如果有人认出它请告诉我,以便我可以参考):
private static byte[] createThumbnail(byte[] bytes)
{
try
{
double scale;
int sizeDifference, originalImageLargestDim;
Image inImage = ImageIO.read(new ByteArrayInputStream(bytes));
//find biggest dimension
if(inImage.getWidth(null) > inImage.getHeight(null))
{
scale = (double)LARGEST_DIMENSION/(double)inImage.getWidth(null);
sizeDifference = inImage.getWidth(null) - LARGEST_DIMENSION;
originalImageLargestDim = inImage.getWidth(null);
}
else
{
scale = (double)LARGEST_DIMENSION/(double)inImage.getHeight(null);
sizeDifference = inImage.getHeight(null) - LARGEST_DIMENSION;
originalImageLargestDim = inImage.getHeight(null);
}
//create an image buffer to draw to
BufferedImage outImage = new BufferedImage(100, 100, BufferedImage.TYPE_INT_RGB); //arbitrary init so code compiles
Graphics2D g2d;
AffineTransform tx;
if(scale < 1.0d) //only scale if desired size is smaller than original
{
int numSteps = sizeDifference / 100;
int stepSize = sizeDifference / numSteps;
int stepWeight = stepSize/2;
int heavierStepSize = stepSize + stepWeight;
int lighterStepSize = stepSize - stepWeight;
int currentStepSize, centerStep;
double scaledW = inImage.getWidth(null);
double scaledH = inImage.getHeight(null);
if(numSteps % 2 == 1) //if there's an odd number of steps
centerStep = (int)Math.ceil((double)numSteps / 2d); //find the center step
else
centerStep = -1; //set it to -1 so it's ignored later
Integer intermediateSize = originalImageLargestDim, previousIntermediateSize = originalImageLargestDim;
for(Integer i=0; i<numSteps; i++)
{
if(i+1 != centerStep) //if this isn't the center step
{
if(i == numSteps-1) //if this is the last step
{
//fix the stepsize to account for decimal place errors previously
currentStepSize = previousIntermediateSize - LARGEST_DIMENSION;
}
else
{
if(numSteps - i > numSteps/2) //if we're in the first half of the reductions
currentStepSize = heavierStepSize;
else
currentStepSize = lighterStepSize;
}
}
else //center step, use natural step size
{
currentStepSize = stepSize;
}
intermediateSize = previousIntermediateSize - currentStepSize;
scale = (double)intermediateSize/(double)previousIntermediateSize;
scaledW = (int)scaledW*scale;
scaledH = (int)scaledH*scale;
outImage = new BufferedImage((int)scaledW, (int)scaledH, BufferedImage.TYPE_INT_RGB);
g2d = outImage.createGraphics();
g2d.setBackground(Color.WHITE);
g2d.clearRect(0, 0, outImage.getWidth(), outImage.getHeight());
g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
tx = new AffineTransform();
tx.scale(scale, scale);
g2d.drawImage(inImage, tx, null);
g2d.dispose();
inImage = new ImageIcon(outImage).getImage();
previousIntermediateSize = intermediateSize;
}
}
else
{
//just copy the original
outImage = new BufferedImage(inImage.getWidth(null), inImage.getHeight(null), BufferedImage.TYPE_INT_RGB);
g2d = outImage.createGraphics();
g2d.setBackground(Color.WHITE);
g2d.clearRect(0, 0, outImage.getWidth(), outImage.getHeight());
tx = new AffineTransform();
tx.setToIdentity(); //use identity matrix so image is copied exactly
g2d.drawImage(inImage, tx, null);
g2d.dispose();
}
//JPEG-encode the image and write to file.
ByteArrayOutputStream os = new ByteArrayOutputStream();
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(os);
encoder.encode(outImage);
return os.toByteArray();
}
catch(Exception e)
{
throw new RuntimeException(e);
}
}
答案 1 :(得分:1)
以下代码将整个图像缩放为一个区域。您可以复制粘贴代码并运行它以查看它的作用。
有趣的调用是g2d.drawImage(img, 0, 0, thumb.getWidth() - 1, thumb.getHeight() - 1, 0, 0, img.getWidth() - 1, img.getHeight() - 1, null);
,它将图像复制到缩略图中,缩放它以适应。
如果您想要不同的缩放比例来保留纵横比,您可以决定在g2d上使用scale(),或者选择不同的源坐标。
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
public class ThumbnailFactory {
public ThumbnailFactory() {
}
public void run(String folder) {
File dir = new File(folder);
for (File file : dir.listFiles()) {
createThumbnail(file);
}
}
private void createThumbnail(File file) {
try {
// BufferedImage is the best (Toolkit images are less flexible)
BufferedImage img = ImageIO.read(file);
BufferedImage thumb = createEmptyThumbnail();
// BufferedImage has a Graphics2D
Graphics2D g2d = (Graphics2D) thumb.getGraphics();
g2d.drawImage(img, 0, 0,
thumb.getWidth() - 1,
thumb.getHeight() - 1,
0, 0,
img.getWidth() - 1,
img.getHeight() - 1,
null);
g2d.dispose();
ImageIO.write(thumb, "PNG", createOutputFile(file));
} catch (Exception e) {
e.printStackTrace();
}
}
private File createOutputFile(File inputFile) {
// You'll want something better than this...
return new File(inputFile.getAbsolutePath()
+ ".thumb.png");
}
private BufferedImage createEmptyThumbnail() {
return new BufferedImage(100, 200,
BufferedImage.TYPE_INT_RGB);
}
public static void main(String[] args) {
ThumbnailFactory fac = new ThumbnailFactory();
fac.run("c:\\images");
}
}