Nvidia公司的深度学习cuDNN中,图像使用一种名为CHW的有趣格式。我有一个cv::Mat img;需要转换为一个浮点数的一维向量。问题是CHW的一维向量格式是(RR...R, GG..G,BB..B)。因此,我想知道该如何提取每个像素的通道值,并按照此格式排序。
#include <opencv2/opencv.hpp>
cv::Mat hwc2chw(const cv::Mat &image){
std::vector<cv::Mat> rgb_images;
cv::split(image, rgb_images);
// Stretch one-channel images to vector
cv::Mat m_flat_r = rgb_images[0].reshape(1,1);
cv::Mat m_flat_g = rgb_images[1].reshape(1,1);
cv::Mat m_flat_b = rgb_images[2].reshape(1,1);
// Now we can rearrange channels if need
cv::Mat matArray[] = { m_flat_r, m_flat_g, m_flat_b};
cv::Mat flat_image;
// Concatenate three vectors to one
cv::hconcat( matArray, 3, flat_image );
return flat_image;
}
顺便说一句,如果输入的图像不是RGB格式,您可以在matArray创建行中更改通道顺序。
cv::Mat bgr_image = cv::imread(imageFileName);
cv::Mat chw_image = cv::dnn::blobFromImage
(
bgr_image,
1.0, // scale factor
cv::Size(), // spatial size for output image
cv::Scalar(), // mean
true, // swapRB: BGR to RGB
false, // crop
CV_32F // Depth of output blob. Choose CV_32F or CV_8U.
);
const float* data = reinterpret_cast<const float*>(chw_image.data);
int data_length = 1 * 3 * bgr_image.rows * bgr_image.cols;
您可以手动迭代图像并将值复制到正确的位置,也可以使用类似 cv::extractChannel 的东西逐个复制通道,如下所示:
#include <opencv2/opencv.hpp>
int main()
{
//create dummy 3 channel float image
cv::Mat sourceRGB(cv::Size(100,100),CV_32FC3);
auto size = sourceRGB.size();
for (int y = 0; y < size.height; ++y)
{
for (int x = 0; x < size.width; ++x)
{
float* pxl = sourceRGB.ptr<float>(x, y);
*pxl = x / 100.0f;
*(pxl+1) = y / 100.0f;
*(pxl + 2) = (y / 100.0f) * (x / 100.0f);
}
}
cv::imshow("test", sourceRGB);
cv::waitKey(0);
//create single image with all 3 channels one after the other
cv::Size newsize(size.width,size.height*3);
cv::Mat destination(newsize,CV_32FC1);
//copy the channels from the source image to the destination
for (int i = 0; i < sourceRGB.channels(); ++i)
{
cv::extractChannel(
sourceRGB,
cv::Mat(
size.height,
size.width,
CV_32FC1,
&(destination.at<float>(size.height*size.width*i))),
i);
}
cv::imshow("test", destination);
cv::waitKey(0);
return 0;
}