如何匹配BufferedImage和Mat的颜色模型？

Question

我正在尝试将BufferedImage转换为Mat，以获取从互联网下载的具有不同文件类型的大量图像。因为我是刮从网站的图像，我没有控制的文件格式。我可以在不知道格式的情况下轻松地将它们加载到BufferedImage，但是要将它们转换为Mat，我需要知道图像类型。不幸的是，CvType和BufferedImage类型之间似乎没有很好的对应关系。

CvType用格式CV_<bit-depth>{U|S|F}C<number_of_channels>表示图像类型，其中U是无符号字符，S是有符号字符，F是浮点。

BufferedImage类型在表示形式上有更多的变化，包括对称通道(TYPE_4BYTE_ABGR)、可变比特数(TYPE_BYTE_BINARY)以及任何索引字节图像(TYPE_BYTE_INDEXED)。

根据文件，我试图完成我自己的信件。

BufferedImage imgBuffer = ImageIO.read(new File("example.gif"));

//Save file as reference
File outputfile = new File("temp/image.png");
ImageIO.write(imgBuffer, "png", outputfile);

//My correspondance
int curCVtype = -1;
switch (imgBuffer.getType()) {
case BufferedImage.TYPE_3BYTE_BGR:
    curCVtype = CvType.CV_8UC3;
    break;
case BufferedImage.TYPE_BYTE_GRAY:
    curCVtype = CvType.CV_8UC1;
    break;
case BufferedImage.TYPE_INT_BGR:
case BufferedImage.TYPE_INT_RGB:
    curCVtype = CvType.CV_8SC3;
    break;
case BufferedImage.TYPE_INT_ARGB:
case BufferedImage.TYPE_INT_ARGB_PRE:
    curCVtype = CvType.CV_8SC4;
    break;
default:
//  The types not handled by my correspondence
//                  BufferedImage.TYPE_BYTE_BINARY;
//                  BufferedImage.TYPE_USHORT_GRAY;
//                  BufferedImage.TYPE_4BYTE_ABGR;
//                  BufferedImage.TYPE_4BYTE_ABGR_PRE;
//                  BufferedImage.TYPE_BYTE_INDEXED;
//                  BufferedImage.TYPE_CUSTOM;

    System.out.println("Unsupported format:" + imgBuffer.getType());
    //Here I choose a default type
    curCVtype = CvType.CV_8SC3;
}

//Convert to Mat
byte[] pixels = ((DataBufferByte) imgBuffer.getRaster().getDataBuffer()).getData();
Mat img = new Mat(imgBuffer.getHeight(), imgBuffer.getWidth(), curCVtype);
img.put(0, 0, pixels);

//Write the output to compare
Imgcodecs.imwrite("temp/image_mat.png", img);

问题

1. 我说得对吗？还是有更好的方法？
2. 对于默认情况下的类型，正确的对应是什么？

示例

输入

​

用BufferedImage转换成PNG

转换成Mat后输出PNG。BufferedImage类型被TYPE_BYTE_INDEXED转换为CvType.CV_8SC3

转换成Mat后输出PNG。BufferedImage类型被TYPE_BYTE_INDEXED转换为CvType.CV_8UC3

​

资源：

我的起始代码来自Converting BufferedImage to Mat in opencv。

我对CvTypes的了解来自于What's the difference between cvtype values in OPENCV?。

Answer 1

感谢Miki和haraldK的有益评论。

我的未知图像类型解决方案以RGB格式检索像素，并将它们放入Mat of CvType.CV_8UC4中。最后，使用Core.mixChannels将信道重新排序为OpenCV优先顺序: BGR(A)。

此示例只为未知图像类型重新排序通道，但所有非BGR图像类型都需要重新排序。

BufferedImage imgBuffer = ImageIO.read(new File("example.gif"));

//Save image as reference
File outputfile = new File("temp/image.png");
ImageIO.write(imgBuffer, "png", outputfile);

//My correspondance

int curCVtype = CvType.CV_8UC4; //Default type
boolean supportedType = true;

switch (imgBuffer.getType()) {
case BufferedImage.TYPE_3BYTE_BGR:
    curCVtype = CvType.CV_8UC3;
    break;
case BufferedImage.TYPE_BYTE_GRAY:
case BufferedImage.TYPE_BYTE_BINARY:
    curCVtype = CvType.CV_8UC1;
    break;
case BufferedImage.TYPE_INT_BGR:
case BufferedImage.TYPE_INT_RGB:
    curCVtype = CvType.CV_32SC3;
    break;
case BufferedImage.TYPE_INT_ARGB:
case BufferedImage.TYPE_INT_ARGB_PRE:
    curCVtype = CvType.CV_32SC4;
    break;
case BufferedImage.TYPE_USHORT_GRAY:
    curCVtype = CvType.CV_16UC1;
    break;
case BufferedImage.TYPE_4BYTE_ABGR:
case BufferedImage.TYPE_4BYTE_ABGR_PRE:
    curCVtype = CvType.CV_8UC4;
    break;
default:
    // BufferedImage.TYPE_BYTE_INDEXED;
    // BufferedImage.TYPE_CUSTOM;
    System.out.println("Unsupported format:" + imgBuffer.getType());
    supportedType = false;
}

//Convert to Mat
Mat img = new Mat(imgBuffer.getHeight(), imgBuffer.getWidth(), curCVtype);
if (supportedType) {
    // Insert pixel buffer directly
    byte[] pixels = ((DataBufferByte) imgBuffer.getRaster().getDataBuffer()).getData();
    img.put(0, 0, pixels);
} else {
    // Convert to RGB first
    int height = imgBuffer.getHeight();
    int width = imgBuffer.getWidth();
    int[] pixels = imgBuffer.getRGB(0, 0, width - 1, height - 1, null, 0, width);

    // Convert ints to bytes
    ByteBuffer byteBuffer = ByteBuffer.allocate(pixels.length * 4);
    IntBuffer intBuffer = byteBuffer.asIntBuffer();
    intBuffer.put(pixels);

    byte[] pixelBytes = byteBuffer.array();

    img.put(0, 0, pixelBytes);

    // Reorder the channels for Opencv BGRA format from
    // BufferedImage ARGB format
    Mat imgMix = img.clone();
    ArrayList<Mat> imgSrc = new ArrayList<Mat>();
    imgSrc.add(imgMix);

    ArrayList<Mat> imgDest = new ArrayList<Mat>();
    imgDest.add(img);

    int[] fromTo = { 0, 3, 1, 2, 2, 1, 3, 0 }; //Each pair is a channel swap
    Core.mixChannels(imgSrc, imgDest, new MatOfInt(fromTo));
}

//Save output image
Imgcodecs.imwrite("temp/image_mat.png", img);

新输出图像

​