Android Yuv420sp for ARGB in OpenCV

Question

I am trying to send a source image from a preview from a phone to a PC. Then the PC will process the image. I use the OpenCV library for image processing. For now, I am just writing a function in previewcallback to save an array of bytes to a file, and copy the file to the computer, and I wrote a simple program for the first reading in the file and saved it to memory, and then directly copied the data to IplImage.imageData. But I always get a garbage image.

I use this function that I found on the network to do the conversion between YUV420SP and ARGB. Thank you for your help.

void decodeYUV420SP(int* rgb, char* yuv420sp, int width, int height) { int frameSize = width * height; for (int j = 0, yp = 0; j < height; j++) { int uvp = frameSize + (j >> 1) * width, u = 0, v = 0; for (int i = 0; i < width; i++, yp++) { int y = (0xff & ((int) yuv420sp[yp])) - 16; if (y < 0) y = 0; if ((i & 1) == 0) { v = (0xff & yuv420sp[uvp++]) - 128; u = (0xff & yuv420sp[uvp++]) - 128; } int y1192 = 1192 * y; int r = (y1192 + 1634 * v); int g = (y1192 - 833 * v - 400 * u); int b = (y1192 + 2066 * u); if (r < 0) r = 0; else if (r > 262143) r = 262143; if (g < 0) g = 0; else if (g > 262143) g = 262143; if (b < 0) b = 0; else if (b > 262143) b = 262143; rgb[yp] = 0xff000000 | ((r << 6) & 0xff0000) | ((g >> 2) & 0xff00) | ((b >> 10) & 0xff); } } } 

Answer 1

YUV420 images are an odd shape, part Y (luminescence) is half the width and height of the image, but it is followed by parts of Cr and Cb with half the width but the height of a quarter.
Usually they are not displayed directly, so no one cares about the odd packaging.

The result is a color image with 1.5 bytes / pixel instead of rgb

Answer 2

You can use OpenCV4Android converters:

 Imgproc.cvtColor(mYuv, mRgba, Imgproc.COLOR_YUV420sp2RGBA); 

Answer 3

Did you manage to do this? If you don't look at the android-opencv project, they have a method for android yuv to bgr.

Answer 4

Based on my understanding, if the image is 640 * 480. In the YUV420 byte buffer, the first 640 * 480 bytes will correspond to the Y-part. And it is followed by 320 * 480 bytes Cb and Cr interleavely, so the first 640 * 480 bytes Y and the next 320 * 480 bytes CbCr, which are reset in a 2 by 2 grid