java - 使用 Java 创建图像的缩略图 View

Question

我有一个应用程序，我需要选择一个包含图片的文件夹，并且需要使用 Java 显示这些图像的缩略图 View 。我不知道如何以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

Answer 1

我在我的一个项目中使用了这段代码。我前段时间在网上找到的(不知道在哪里，但如果有人知道请告诉我，以便我引用):

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);
    }
}