用opencv怎么将bgr图片nv12 ?

将BGR图像转换为NV12格式可以通过以下步骤完成：

1. 使用OpenCV的cvtColor函数将BGR图像转换为YUV格式。例如：

cv::Mat bgrImage = cv::imread("input_image.jpg");
cv::Mat yuvImage;
cv::cvtColor(bgrImage, yuvImage, cv::COLOR_BGR2YUV_I420);

2. 将I420格式的YUV图像转换为NV12格式。NV12格式与I420格式的区别是UV分量的存储方式不同。在I420中，U和V分量是交错存储的，而在NV12中，U和V分量是连续存储的。以下是将I420格式的YUV图像转换为NV12格式的代码：

int width = bgrImage.cols;
int height = bgrImage.rows;

// Get the number of pixels in the image
int numPixels = width * height;

// Calculate the size of the U and V planes
int uvSize = numPixels / 4;

// Get pointers to the Y, U, and V planes
uchar* yPlanePtr = yuvImage.data;
uchar* uPlanePtr = yPlanePtr + numPixels;
uchar* vPlanePtr = uPlanePtr + uvSize;

// Create a new buffer for the NV12 image
std::vector<uchar> nv12Image(numPixels + uvSize);

// Copy the Y plane to the NV12 buffer
std::copy(yPlanePtr, yPlanePtr + numPixels, nv12Image.begin());

// Interleave the U and V planes and copy them to the NV12 buffer
for (int i = 0; i < uvSize; i++) {
    nv12Image[numPixels + i * 2] = uPlanePtr[i];
    nv12Image[numPixels + i * 2 + 1] = vPlanePtr[i];
}

// Create a new Mat object for the NV12 image and copy the buffer to it
cv::Mat nv12Mat(height + height / 2, width, CV_8UC1, nv12Image.data());

现在，您可以将`nv12Mat`用作NV12格式的图像。