My batch jpg resizer works with color images, but grayscale ones become washed out

I've been having a problem with my Java program. It's for resizing images. You drop it into a folder and run it, and it creates a new folder with the resized images. It works great on colo开发者_开发问答r, but it has a problem with grayscale. The images are converted, but they become lighter and more washed out, as if someone has messed with the curves or levels. All the input files and output files are sRGB color space jpegs, saved in RGB color mode. I have thousands of 50 megapixel film scans I'm trying to convert down to 15 megapixels or less. Any help or ideas anyone could offer would be most appreciated. The programs full code is below, it's about 130 lines. I have a feeling the problem may be in the toBufferedImage function but I'm lost as to what it could be.

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"));
    }
}

If jdk's classes and methods are buggy, report the bug to oracle (oh! I wish I could go on saying to SUN..).

And, while the next release will correct the bug ;), try some work arounds, scaling image by yourself like proposed here.

Regards, Stéphane

In your code, you assume jpeg are encoded in RGB, but that's not always the case. It's also possible to encode 8 bit gray scaled jpeg. So I suggest that you try this when building your BufferedImage, replace :

BufferedImage.TYPE_INT_RGB;

by

BufferedImage.TYPE_BYTE_GRAY;

and see if it works for those images.

If so, then you still have to find out a way to determine the encoding type to automatically change the type of BufferedImage color encoding to use, but you will be one stop closer.

Regards, Stéphane