如何正确地在Java中从CMYK转换为RGB？

问题描述

我将用于将CMYK jpeg转换为RGB的Java代码导致输出图像太亮 - 请参阅下面的代码。任何人都可以建议正确的转换方式吗？

My Java code to convert a CMYK jpeg to RGB results in the output image being far too light - see code below. Can anyone suggest the correct way to do the conversion?

以下代码需要，用于阅读jpeg和

The following code requires Java Advanced Image IO to read the jpeg and example-cmyk.jpg

import java.awt.image.BufferedImage;
import java.awt.image.ColorConvertOp;
import java.io.File;

import javax.imageio.ImageIO;

public class TestCmykToRgb {

    public static void main(String[] args) throws Exception {
        BufferedImage cmykImage = ImageIO.read(new File(
                "j:\\temp\\example-cmyk.jpg"));


        BufferedImage rgbImage = new BufferedImage(cmykImage.getWidth(),
                cmykImage.getHeight(), BufferedImage.TYPE_INT_RGB);

        ColorConvertOp op = new ColorConvertOp(null);
        op.filter(cmykImage, rgbImage);

        ImageIO.write(rgbImage, "JPEG", new File("j:\\temp\\example-rgb.jpg"));

    }
}

推荐答案

现有答案中已有很多好东西。但它们都不是处理不同类型的CMYK JPEG图像的完整解决方案。

There is a lot of good stuff in the existing answers already. But none of them is a complete solution that handles the different kinds of CMYK JPEG images.

对于CMYK JPEG图像，您需要区分常规CMYK，Adobe CMYK（与反转值，即255表示没有墨水，0表示最大墨水）和Adobe CYYK（某些变体也有反转颜色）。

For CMYK JPEG images, you need to distinguish between regular CMYK, Adobe CMYK (with inverted values, i.e. 255 for no ink and 0 for maximum ink) and Adobe CYYK (some variant with inverted colors as well).

此解决方案需要Sanselan（或Apache）现在称为Commons Imaging，它需要合理的CMYK颜色配置文件（.icc文件）。你可以从Adobe或eci.org获得后者。

This solution here requires Sanselan (or Apache Commons Imaging as it's called now) and it requires a reasonable CMYK color profile (.icc file). You can get the later one from Adobe or from eci.org.

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);
}

代码首先尝试使用常规方法读取文件，该方法适用于RGB文件。如果失败，则会读取颜色模型的详细信息（配置文件，Adobe标记，Adobe变体）。然后它读取原始像素数据（光栅）并进行所有必要的转换（YCCK到CMYK，反转颜色，CMYK到RGB）。

The code first tries to read the file using the regular method, which works for RGB files. If it fails, it reads the details of the color model (profile, Adobe marker, Adobe variant). Then it reads the raw pixel data (raster) and does all the necessary conversion (YCCK to CMYK, inverted colors, CMYK to RGB).

更新：

原始代码有一个小问题：结果太亮了。来自12monkeys-imageio项目的人们遇到了同样的问题（见）并通过修补颜色配置文件修复它，以便Java使用感知颜色渲染意图。该修补程序已集成到上面的代码中。

The original code has a slight problem: the result was too bright. The people from the twelvemonkeys-imageio project had the same problem (see this post) and have fixed it by patching the color profile such that Java uses a perceptual color render intent. The fix has been integrated into the above code.

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