如何从 url 中读取图像并在 java 中将其从 CMYK 转换为 RGB？

Question

我正在尝试从特定 URL 读取图像并将其从 CMYK 转换为 RGB。我手动将图像保存到一个文件中，并使用“How to convert from CMYK to RGB in Java correctly?”中的代码来执行此操作。它工作正常，但如果我想从 URL 读取它怎么办？

代码如下：

    public class JpegReader {

    public static final int COLOR_TYPE_RGB = 1;
    public static final int COLOR_TYPE_CMYK = 2;
    public static final int COLOR_TYPE_YCCK = 3;

    private int colorType = COLOR_TYPE_RGB;
    private boolean hasAdobeMarker = false;

    public BufferedImage readImage(File file) throws IOException, ImageReadException {
        colorType = COLOR_TYPE_RGB;
        hasAdobeMarker = false;

        ImageInputStream stream = ImageIO.createImageInputStream(file);
        Iterator<ImageReader> iter = ImageIO.getImageReaders(stream);
        while (iter.hasNext()) {
            ImageReader reader = iter.next();
            reader.setInput(stream);

            BufferedImage image;
            ICC_Profile profile = null;
            try {
                image = reader.read(0);
            } catch (IIOException e) {
                colorType = COLOR_TYPE_CMYK;
                checkAdobeMarker(file);
                profile = Sanselan.getICCProfile(file);
                WritableRaster raster = (WritableRaster) reader.readRaster(0, null);
                if (colorType == COLOR_TYPE_YCCK)
                    convertYcckToCmyk(raster);
                if (hasAdobeMarker)
                    convertInvertedColors(raster);
                image = convertCmykToRgb(raster, profile);
            }

            return image;
        }

        return null;
    }

    public void checkAdobeMarker(File file) throws IOException, ImageReadException {
        JpegImageParser parser = new JpegImageParser();
        ByteSource byteSource = new ByteSourceFile(file);
        @SuppressWarnings("rawtypes")
        ArrayList segments = parser.readSegments(byteSource, new int[] { 0xffee }, true);
        if (segments != null && segments.size() >= 1) {
            UnknownSegment app14Segment = (UnknownSegment) segments.get(0);
            byte[] data = app14Segment.bytes;
            if (data.length >= 12 && data[0] == 'A' && data[1] == 'd' && data[2] == 'o' && data[3] == 'b' && data[4] == 'e')
            {
                hasAdobeMarker = true;
                int transform = app14Segment.bytes[11] & 0xff;
                if (transform == 2)
                    colorType = COLOR_TYPE_YCCK;
            }
        }
    }

    public static void convertYcckToCmyk(WritableRaster raster) {
        int height = raster.getHeight();
        int width = raster.getWidth();
        int stride = width * 4;
        int[] pixelRow = new int[stride];
        for (int h = 0; h < height; h++) {
            raster.getPixels(0, h, width, 1, pixelRow);

            for (int x = 0; x < stride; x += 4) {
                int y = pixelRow[x];
                int cb = pixelRow[x + 1];
                int cr = pixelRow[x + 2];

                int c = (int) (y + 1.402 * cr - 178.956);
                int m = (int) (y - 0.34414 * cb - 0.71414 * cr + 135.95984);
                y = (int) (y + 1.772 * cb - 226.316);

                if (c < 0) c = 0; else if (c > 255) c = 255;
                if (m < 0) m = 0; else if (m > 255) m = 255;
                if (y < 0) y = 0; else if (y > 255) y = 255;

                pixelRow[x] = 255 - c;
                pixelRow[x + 1] = 255 - m;
                pixelRow[x + 2] = 255 - y;
            }

            raster.setPixels(0, h, width, 1, pixelRow);
        }
    }

    public static void convertInvertedColors(WritableRaster raster) {
        int height = raster.getHeight();
        int width = raster.getWidth();
        int stride = width * 4;
        int[] pixelRow = new int[stride];
        for (int h = 0; h < height; h++) {
            raster.getPixels(0, h, width, 1, pixelRow);
            for (int x = 0; x < stride; x++)
                pixelRow[x] = 255 - pixelRow[x];
            raster.setPixels(0, h, width, 1, pixelRow);
        }
    }

    public static BufferedImage convertCmykToRgb(Raster cmykRaster, ICC_Profile cmykProfile) throws IOException {
        if (cmykProfile == null)
            cmykProfile = ICC_Profile.getInstance(JpegReader.class.getResourceAsStream("/ISOcoated_v2_300_eci.icc"));

        if (cmykProfile.getProfileClass() != ICC_Profile.CLASS_DISPLAY) {
            byte[] profileData = cmykProfile.getData();

            if (profileData[ICC_Profile.icHdrRenderingIntent] == ICC_Profile.icPerceptual) {
                intToBigEndian(ICC_Profile.icSigDisplayClass, profileData, ICC_Profile.icHdrDeviceClass); // Header is first

                cmykProfile = ICC_Profile.getInstance(profileData);
            }
        }

        ICC_ColorSpace cmykCS = new ICC_ColorSpace(cmykProfile);
        BufferedImage rgbImage = new BufferedImage(cmykRaster.getWidth(), cmykRaster.getHeight(), BufferedImage.TYPE_INT_RGB);
        WritableRaster rgbRaster = rgbImage.getRaster();
        ColorSpace rgbCS = rgbImage.getColorModel().getColorSpace();
        ColorConvertOp cmykToRgb = new ColorConvertOp(cmykCS, rgbCS, null);
        cmykToRgb.filter(cmykRaster, rgbRaster);
        return rgbImage;
    }
}


static void intToBigEndian(int value, byte[] array, int index) {
    array[index]   = (byte) (value >> 24);
    array[index+1] = (byte) (value >> 16);
    array[index+2] = (byte) (value >>  8);
    array[index+3] = (byte) (value);
}

Answer 1

我用它来读取来自 url 的图像，希望它对你有用

try{
        URL url = new URL("you link here");
        InputStream is = url.openStream();
        OutputStream os = new FileOutputStream("you local path to save");

        byte[] b = new byte[4096];
        int length;

        while ((length = is.read(b)) != -1) {
            os.write(b, 0, length);
        }

        is.close();
        os.close();

        }catch(Exception exp){
            exp.printStackTrace(); 

        }

Answer 2

你不需要在我的 answer 中做太多改变。 ImageIO.createImageInputStream 方法可以使用 InputStream 而不是文件。

所以在最简单的情况下，您可以像这样更改代码：

public BufferedImage readImage(String imageUrl) throws IOException, ImageReadException {

    /* some code omitted */

    URL url = new URL(imageUrl;
    ImageInputStream stream = ImageIO.createImageInputStream(url.openStream());

更新

由于需要多次输入数据，所以先将其读入字节数组，然后继续使用字节数组是有意义的：

byte[] readIntoByteArray(URL url) throws IOException {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    InputStream is = url.openStream ();

    byte[] buffer = new byte[4096];
    int n;
    while ( (n = is.read(buffer)) > 0 ) {
        baos.write(bufer, 0, n);
    }

    return boas. toByteArray();
}

public BufferedImage readImage(String imageUrl) throws IOException, ImageReadException {

    /* code omitted */

    byte[] imageData = readIntoByteArray(imageUrl);
    ImageInputStream stream = ImageIO.createImageInputStream(new ByteArrayInputStream(imageData));

    /* code omitted */
}


public void checkAdobeMarker(byte[] imageData) throws IOException, ImageReadException {
    JpegImageParser parser = new JpegImageParser();
    ByteSource byteSource = new ByteSourceArray(imageData);

     /* code omitted */
}

Answer 3

接受的答案很好，但如果你想让自己的事情变得更容易，你可以使用 TwelveMonkeys JPEG plugin for ImageIO。它是纯粹的 Java，自动处理 CMYK/YCCK 到 RGB（以及 "real-world" JPEG 中的许多其他问题）并附带非常适合商业使用的 BSD 许可证。

有了这个插件，您的代码可以简单地是：

URL yourURL;
BufferedImage image = ImageIO.read(yourURL);

如何从 url 中读取图像并在 java 中将其从 CMYK 转换为 RGB？

how to read an image from a url and convert it from CMYK to RGB in java?

java

cmyk

javax.imageio