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我正在尝试提高从 BufferedImage 生成的图像的质量。最终目标是输入 JPEG(这里是从计算机上的文件中检索),转换为灰度 TIFF,然后作为字节数组输出。我已经包含了将最终图像保存到 PC 的代码,因此更容易识别问题。

import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.DataBuffer;
import java.awt.image.IndexColorModel;
import java.awt.image.MultiPixelPackedSampleModel;
import java.awt.image.SampleModel;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageReadParam;
import javax.imageio.ImageReader;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.stream.ImageInputStream;
import javax.imageio.stream.ImageOutputStream;
import javax.media.jai.ImageLayout;
import javax.media.jai.JAI;
import javax.media.jai.KernelJAI;
import javax.media.jai.LookupTableJAI;
import javax.media.jai.PlanarImage;
import javax.media.jai.operator.ErrorDiffusionDescriptor;

public class ByteConversionService {

    private static ByteArrayOutputStream baos;
    private static ImageWriter writer;
    private static ImageOutputStream ios;
    private static ImageWriteParam writeParam;

    public static void main(String args[]) {
        try {
            convertBufferedImageToByteArray();
        } catch (Exception e) {

        }
    }

    private static byte[] convertBufferedImageToByteArray()
            throws Exception {
        byte[] convertedByteArray = null;
        resourceSetup();
        try {                   
            File file = new File("../proj/src/image.jpg");
            BufferedImage image = ImageIo.read(file);
            convertImageToTif(image);
            createImage(baos);
            convertedByteArray = baos.toByteArray();
        } finally {
            resourceCleanup();
        }   
        return convertedByteArray;
    }

    private static void resourceSetup() throws Exception {
        baos = new ByteArrayOutputStream();
        writer = ImageIO.getImageWritersByFormatName(
                "tif").next();
        ios = ImageIO.createImageOutputStream(baos);
        writer.setOutput(ios);
        writeParam = writer.getDefaultWriteParam();
        writeParamSetUp(writeParam);
    }

    private static void writeParamSetUp(ImageWriteParam writeParam) {
        writeParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        writeParam.setCompressionType("CCITT T.4");
    }

    private static void convertImageToTif(BufferedImage image) throws Exception {
        try {
            BufferedImage blackAndWhiteImage = imageToBlackAndWhite(image);
            writeToByteArrayStream(blackAndWhiteImage);
            IIOImage iioImage = new IIOImage(blackAndWhiteImage, null, null);
            writer.write(null, iioImage, writeParam);
        } finally {
            image.flush();
        }
    }

    private static BufferedImage imageToBlackAndWhite(BufferedImage image) {
        PlanarImage surrogateImage = PlanarImage.wrapRenderedImage(image);
        LookupTableJAI lut = new LookupTableJAI(new byte[][] {
                { (byte) 0x00, (byte) 0xff }, { (byte) 0x00, (byte) 0xff },
                { (byte) 0x00, (byte) 0xff } });
        ImageLayout layout = new ImageLayout();
        byte[] map = new byte[] { (byte) 0x00, (byte) 0xff };
        ColorModel cm = new IndexColorModel(1, 2, map, map, map);
        layout.setColorModel(cm);
        SampleModel sm = new MultiPixelPackedSampleModel(DataBuffer.TYPE_BYTE,
                surrogateImage.getWidth(), surrogateImage.getHeight(), 1);
        layout.setSampleModel(sm);
        RenderingHints hints = new RenderingHints(JAI.KEY_IMAGE_LAYOUT, layout);
        PlanarImage op = ErrorDiffusionDescriptor.create(surrogateImage, lut,
                KernelJAI.ERROR_FILTER_FLOYD_STEINBERG, hints);
        BufferedImage blackAndWhiteImage = op.getAsBufferedImage();
        return blackAndWhiteImage;
    }

    private static void writeToByteArrayStream(BufferedImage image) throws Exception {
        ImageIO.write(image, "tif", baos);
    }

    private static void createImage(ByteArrayOutputStream baos) throws Exception {
        ByteArrayInputStream bis = new ByteArrayInputStream(baos.toByteArray());
        ImageReader reader = (ImageReader) ImageIO.getImageReadersByFormatName(
                "tif").next();
        Object source = bis;
        ImageInputStream iis = ImageIO.createImageInputStream(source);
        reader.setInput(iis, true);
        ImageReadParam param = reader.getDefaultReadParam();
        Image image = reader.read(0, param);
        BufferedImage buffered = new BufferedImage(image.getWidth(null),
                image.getHeight(null), BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = buffered.createGraphics();
        g2.drawImage(image, null, null);
        File file = new File("../proj/src/image2.tif");
        ImageIO.write(buffered, "tif", file);
    }

    private static void resourceCleanup() throws Exception {
        ios.flush();
        ios.close();
        baos.flush();
        baos.close();
        writer.dispose();
    }
}

当前的问题是最终图像质量低下 - 放大显示构成图片的像素之间存在大量空白。我的理解是这可能是由于使用了抖动算法(Floyd-Steinberg),所以图像在技术上不是以灰度再现的。

我尝试了多种解决方案,我将在评论中发布,但没有成功。我的问题是,我当前的解决方案是否可以提高最终质量,或者我的灰度转换是否存在缺陷,并且该imageToBlackAndWhite方法不适合我的需求。

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1 回答 1

1

现在我们已经确定所需的结果确实是灰度图像,我们可以修复代码以便生成灰度 TIFF。

有两件事需要改变,首先是从 RGB 到灰色的色彩空间转换:

private static BufferedImage imageToBlackAndWhite(BufferedImage image) {
    ColorSpace cs = ColorSpace.getInstance(ColorSpace.CS_GRAY);
    ColorConvertOp op = new ColorConvertOp(cs, null);  
    return op.filter(image, null);
}

我更喜欢ColorConvertOp,因为它是最“正确”的,并且在大多数平台上都使用本机代码。但是您列出的任何其他方法也应该有效。为了清楚起见,您可能还需要考虑将方法重命名imageToGrayScale为 。

此外,您需要更改 TIFF 压缩设置,因为 CCITT T.4 压缩只能用于二进制黑白图像(它是为传真传输创建的)。如果您可以接受有损压缩,我建议您使用 Deflate 或 LZW 压缩,或者 JPEG。这些都适用于灰度数据:

private static void writeParamSetUp(ImageWriteParam writeParam) {
    writeParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
    writeParam.setCompressionType("Deflate"); // or LZW or JPEG
} 

PS:您还应该摆脱该writeToByteArrayStream方法,因为您当前的代码两次写入 TIFF,一次使用 未压缩ImageIO.write(...),然后使用 压缩一次writer.write(...)

PPS:该createImage方法也可以简化很多,因为它ByteArrayOutputStream已经包含完整的 TIFF。

private static void createImage(ByteArrayOutputStream baos) throws Exception {
    File file = new File("../proj/src/image2.tif");
    Files.write(file.toPath(), baos.toByteArray(), StandardOpenOption.CREATE);
}
于 2017-01-11T14:28:13.610 回答