如何匹配BufferedImage和Mat的颜色模型？

Question

我想转换BufferedImage到Mat一个大集从互联网上下载不同的文件类型的图像。因为我从网站上抓取图像，所以我无法控制文件格式。我可以很容易地BufferedImage将它们加载到而不知道格式，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类型之间似乎并没有很好的对应关系。

CvType表示图像类型的格式CV_<bit-depth>{U|S|F}C<number_of_channels>，其中U被无符号字符，S则符号的字符，并且F是浮动。

BufferedImage类型的表示形式更加多样化，包括对称通道（TYPE_4BYTE_ABGR），位数不等（TYPE_BYTE_BINARY）以及任何索引的字节映像（TYPE_BYTE_INDEXED）。

根据文档，我尝试完成我自己的信件。

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. 我能正确处理吗？还是有更好的方法？
2. 在我的默认情况下，这些类型的正确对应关系是什么？

例子

输入项

转换为PNG BufferedImage

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

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

资源：

我的起始代码来自opencv中将BufferedImage转换为Mat。

我对CvType的了解来自于OPENCV中cvtype值之间的区别是什么？。

Answer 1

感谢Miki和haraldK的有用评论。

我针对未知图像类型的解决方案检索RGB格式的像素，并将其放入的Mat中CvType.CV_8UC4。最后，使用Core.mixChannelsOpenCV首选顺序：BGR（A）对频道重新排序。

此示例仅对未知图像类型的通道重新排序，但是所有非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);

新的输出图像