java - 在 Java 中调整 jpeg 大小时丢失颜色(尝试使用多个库)

Question

我已经尝试过在 SO 上发布的多个图像大小调整库，以及使用 getScaledInstance 的原始 java。虽然大部分时间一切正常，但有两张 jpeg 图像，每当我调整它们的大小时，它们的颜色总是乱七八糟。

第一张图片:

结果:

第二张图片:

结果:

我已经使用 image.getScaledInstance() 尝试使用多个库(包括 Scalr、Thumbnailator 和 raw java)处理这些图像(代码请参见 here)，但结果是一样的。

知道问题出在哪里吗？

Answer 1

在 this answer 的大力帮助下，我找到了解决方案:

import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.RenderingHints;
import java.awt.Toolkit;
import java.awt.Transparency;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
import javax.swing.JPanel;

public class ImgUtility
{

    /**
     * Takes a file, and resizes it to the given width and height, while keeping
     * original proportions. Note: It resizes a new file rather than resizing 
     * the original one. Resulting file is always written as a png file due to issues
     * with resizing jpeg files which results in color loss. See:
     * https://stackoverflow.com/a/19654452/49153 
     * for details, including the comments.
     * 
     */    
    public static File resize(File file, int width, int height) throws Exception
    {
        Image img = Toolkit.getDefaultToolkit().getImage( file.getAbsolutePath() );
        loadCompletely(img);
        BufferedImage bm = toBufferedImage(img);
        bm = resize(bm, width, height);

        StringBuilder sb = new StringBuilder();
        sb.append( bm.hashCode() ).append(".png");
        String filename = sb.toString(); 

        File result = new File( filename );
        ImageIO.write(bm, "png", result);

        return result;
    }

    public static BufferedImage toBufferedImage(Image img)
    {
        if (img instanceof BufferedImage)
        {
            return (BufferedImage) img;
        }

        BufferedImage bimage = new BufferedImage(img.getWidth(null), img.getHeight(null), BufferedImage.TYPE_INT_ARGB);

        bimage.getGraphics().drawImage(img, 0, 0 , null);
        bimage.getGraphics().dispose();

        return bimage;
    }

    public static BufferedImage resize(BufferedImage image, int areaWidth, int areaHeight)
    {
        float scaleX = (float) areaWidth / image.getWidth();
        float scaleY = (float) areaHeight / image.getHeight();
        float scale = Math.min(scaleX, scaleY);
        int w = Math.round(image.getWidth() * scale);
        int h = Math.round(image.getHeight() * scale);

        int type = image.getTransparency() == Transparency.OPAQUE ? BufferedImage.TYPE_INT_RGB : BufferedImage.TYPE_INT_ARGB;

        boolean scaleDown = scale < 1;

        if (scaleDown) {
            // multi-pass bilinear div 2
            int currentW = image.getWidth();
            int currentH = image.getHeight();
            BufferedImage resized = image;
            while (currentW > w || currentH > h) {
                currentW = Math.max(w, currentW / 2);
                currentH = Math.max(h, currentH / 2);

                BufferedImage temp = new BufferedImage(currentW, currentH, type);
                Graphics2D g2 = temp.createGraphics();
                g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
                g2.drawImage(resized, 0, 0, currentW, currentH, null);
                g2.dispose();
                resized = temp;
            }
            return resized;
        } else {
            Object hint = scale > 2 ? RenderingHints.VALUE_INTERPOLATION_BICUBIC : RenderingHints.VALUE_INTERPOLATION_BILINEAR;

            BufferedImage resized = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
            Graphics2D g2 = resized.createGraphics();
            g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, hint);
            g2.drawImage(image, 0, 0, w, h, null);
            g2.dispose();
            return resized;
        }
    }


    /**
     * Since some methods like toolkit.getImage() are asynchronous, this
     * method should be called to load them completely.
     */
    public static void loadCompletely (Image img)
    {
        MediaTracker tracker = new MediaTracker(new JPanel());
        tracker.addImage(img, 0);
        try {
            tracker.waitForID(0);
        } catch (InterruptedException ex) {
            throw new RuntimeException(ex);
        }
    }
}