使用Android二进制文件使用openCV Matrix裁剪图像

Question

I'm running into problems cropping an image using the Android OpenCV binaries.

This is what I'm doing to try to crop the upper left quadrant of the image:

Initialization {
    mYuv = new Mat(mFrameSize.height + mFrameSize.height / 2, mFrameSize.width, CvType.CV_8UC1);
    mGraySubmat = mYuv.submat(0, mFrameSize.height, 0, mFrameSize.width);
}


processFrame(byte[] data) {
   mYuv.put(0, 0, data);
   Imgproc.cvtColor(mGraySubmat, mRgba, Imgproc.COLOR_GRAY2BGR, 4);
   bmp = Bitmap.createBitmap(mFrameSize.width/2, mFrameSize.height/2, Bitmap.Config.ARGB_8888);
   Rect roi = new Rect(0,0,mFrameSize.width/2,mFrameSize.height/2);
   Mat faceMat = new Mat(mRgba,roi);
   Utils.matToBitmap(faceMat.clone(), bmp);       

}

What I get is a garbled image. I've seen other posts that say to do what I'm doing but it's not working. Actually the image looks like it's there but there are also shadow images that are out of proportion.

I can do this manually and it works file - see below. Am I doing something wrong?

processFrame(byte[] data) {

     for (int i = 0; i < frameSize; i++) {
     int y = (0xff & ((int) data[i]));
     rgba[i] = 0xff000000 + (y << 16) + (y << 8) + y;
}
// Example of cropping the upper left corder
bmp = Bitmap.createBitmap(mFrameSize.width/2, mFrameSize.height/2, Bitmap.Config.RGB_565);
bmp.setPixels(rgba, 0/* offset */, mFrameSize.width /* stride */, 0, 0, mFrameSize.width/2, mFrameSize.height/2);

Answer 1

I guess you start from this example . In this original source you can see that there is no Imgproc.COLOR_GRAY2BGR conversion. If you want to have a color image then you need to use choice two:

Imgproc.cvtColor(mYuv, mRgba, Imgproc.COLOR_YUV420sp2RGB, 4);

and you do not need mGraySubmat.

If you need grayscale image then the first choice is better:

Imgproc.cvtColor(mGraySubmat, mRgba, Imgproc.COLOR_GRAY2RGBA, 4);

This latter choice truncates the chrominance components of the default preview format what is a YCbCr_420_SP (NV21) formatted image.