我的批量 jpg 缩放器适用于彩色图像，但灰度图像会被冲掉

Question

我的 Java 程序遇到了问题。它用于调整图像大小。您将其放入文件夹并运行它，它会创建一个包含调整大小的图像的新文件夹。它在颜色上效果很好，但在灰度上有问题。图像被转换，但它们变得更亮，更褪色，就好像有人弄乱了曲线或水平。所有输入文件和输出文件都是sRGB颜色空间jpeg，以RGB颜色模式保存。我有数千张 50 兆像素的胶片扫描件，我正在尝试将其转换为 15 兆像素或更低。任何人可以提供的任何帮助或想法将不胜感激。程序完整代码如下，大约130行。我有一种感觉问题可能出在 toBufferedImage 函数中，但我不知道它可能是什么。

package jpegresize;

import java.awt.*;
import java.awt.image.*;
import java.util.*;
import java.io.*;
import javax.imageio.*;
import javax.imageio.stream.*;
import javax.swing.*;

public class Main {

public static void main(String[] args) {

    System.out.println("JPEGResize running . . .");

    int max_side = 4096;
    float quality = 0.9f;

    if(args.length == 0) System.out.println("No maximum side resolution or compression quality arguments given, using default values.\nUsage: java -jar JPEGResize.jar <maximum side resolution in pixels> <quality 0 to 100 percent>");
    if(args.length >= 1) max_side = Integer.parseInt(args[0]);
    if(args.length >= 2) quality = Float.parseFloat(args[1]) / 100.0f;

    System.out.println("Maximum side resolution: " + max_side);
    System.out.println("Compression quality: " + (quality * 100) + "%");

    File folder = new File(".");
    File[] listOfFiles = folder.listFiles(new JPEGFilter());

    for(int i = 0; i < listOfFiles.length; i++) {

        System.out.println("Processing " + listOfFiles[i].getName() + " . . .");
        resizeFile(listOfFiles[i].getName(), max_side, quality);
        System.out.println("Saved /resized/" + listOfFiles[i].getName());
    }

    System.out.println("Operations complete.");
}

public static void resizeFile(String filename, int max_side, float quality) {

    try
    {
        BufferedImage input_img = ImageIO.read(new File(filename));

        double aspect_ratio = ((double)input_img.getWidth()) / ((double)input_img.getHeight());
        int width, height;

        if(input_img.getWidth() >= input_img.getHeight()) {

            width = max_side;
            height = (int)(((double)max_side) / aspect_ratio);
        }
        else {

            width = (int)(((double)max_side) * aspect_ratio);
            height = max_side;
        }

        Image scaled_img = input_img.getScaledInstance(width, height, Image.SCALE_SMOOTH);
        BufferedImage output_img = toBufferedImage(scaled_img);

        Iterator iter = ImageIO.getImageWritersByFormatName("jpeg");
        ImageWriter writer = (ImageWriter)iter.next();
        ImageWriteParam iwp = writer.getDefaultWriteParam();
        iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        iwp.setCompressionQuality(quality);

        File doesDirExist = new File("resized/");
        if(!doesDirExist.exists())
            new File("resized").mkdir();

        File file = new File("resized/" + filename);
        FileImageOutputStream output = new FileImageOutputStream(file);
        writer.setOutput(output);
        IIOImage image = new IIOImage(output_img, null, null);
        writer.write(null, image, iwp);
        writer.dispose();
    }
    catch (IOException e)
    {
        e.printStackTrace();
    }
}

// This method returns a buffered image with the contents of an image
public static BufferedImage toBufferedImage(Image image) {
    if (image instanceof BufferedImage) {
        return (BufferedImage)image;
    }

    // This code ensures that all the pixels in the image are loaded
    image = new ImageIcon(image).getImage();

    // Create a buffered image with a format that's compatible with the screen
    BufferedImage bimage = null;
    GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
    try {
        // Determine the type of transparency of the new buffered image
        int transparency = Transparency.OPAQUE;

        // Create the buffered image
        GraphicsDevice gs = ge.getDefaultScreenDevice();
        GraphicsConfiguration gc = gs.getDefaultConfiguration();
        bimage = gc.createCompatibleImage(
            image.getWidth(null), image.getHeight(null), transparency);
    } catch (HeadlessException e) {
        // The system does not have a screen
    }

    if (bimage == null) {
        // Create a buffered image using the default color model
        int type = BufferedImage.TYPE_INT_RGB;
        bimage = new BufferedImage(image.getWidth(null), image.getHeight(null), type);
    }

    // Copy image to buffered image
    Graphics g = bimage.createGraphics();

    // Paint the image onto the buffered image
    g.drawImage(image, 0, 0, null);
    g.dispose();

    return bimage;
}
}

class JPEGFilter implements FilenameFilter {
public boolean accept(File dir, String name) {
    return (name.toLowerCase().endsWith(".jpg")) || (name.toLowerCase().endsWith(".jpeg"));
    }
}

Answer 1

如果jdk的类和方法有bug，请将bug报告给oracle（哦！我希望我能继续对SUN说..）。

并且，虽然下一个版本将纠正该错误；），但请尝试一些解决方法，自行缩放图像，例如

问候，
史蒂芬

Answer 2

在您的代码中，您假设 jpeg 以 RGB 编码，但情况并非总是如此。还可以对 8 位灰度 jpeg 进行编码。因此，我建议您在构建 BufferedImage 时尝试此操作，将 : 替换

BufferedImage.TYPE_INT_RGB;

为

BufferedImage.TYPE_BYTE_GRAY;

，看看它是否适用于这些图像。

如果是这样，那么您仍然需要找到一种方法来确定编码类型，以自动更改要使用的 BufferedImage 颜色编码类型，但您会更近一步。

问候，
史蒂芬