CODEWITHSUNDEEP
c++opencvimage-processingcaffe
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Reputation: 5434

Converting Caffe caffe::Datum to OpenCV cv::Mat in C++

I'm doing some debugging and so I'm dumping image files to look at the predictions and transformations.

I can create a caffe::Datum from cv::Mat:

cv::Mat matrix;
// ... initialize matrix
caffe::Datum datum;
caffe::CVMatToDatum(matrix, &datum)

but how do I create a cv::Mat from caffe::Datum? The following code gives the fatal exception "Datum not encoded":

caffe::Datum datum;
// ... initialize datum
cv::Mat matrix;
matrix = DecodeDatumToCVMat(datum, true);

Upvotes: 1

Views: 1310

Answers (2)

Shazar
Shazar

Reputation: 13

Addition to the answer by @ttagu99 , in the float section there is a slight bug: The line:

ptr[img_index++] = static_cast<float>(datum.float_data(img_index));

Should be in fact:

int datum_index = (c * datum_height + h) * datum_width + w;
ptr[img_index++] = static_cast<float>(datum->float_data(datum_index));

This fixes the order of writing the data to the matrix. Otherwise, you only see lines of color.

Upvotes: 0

ttagu99
ttagu99

Reputation: 46

You can use following functions.

cv::Mat DatumToCVMat(const Datum& datum){
int datum_channels = datum.channels();
int datum_height = datum.height();
int datum_width = datum.width();

string strData = datum.data();
cv::Mat cv_img;
if (strData.size() != 0)
{
    cv_img.create(datum_height, datum_width, CV_8UC(datum_channels));
    const string& data = datum.data();
    std::vector<char> vec_data(data.c_str(), data.c_str() + data.size());

    for (int h = 0; h < datum_height; ++h) {
        uchar* ptr = cv_img.ptr<uchar>(h);
        int img_index = 0;
        for (int w = 0; w < datum_width; ++w) {
            for (int c = 0; c < datum_channels; ++c) {
                int datum_index = (c * datum_height + h) * datum_width + w;
                ptr[img_index++] = static_cast<uchar>(vec_data[datum_index]);
            }
        }
    }
}
else
{
    cv_img.create(datum_height, datum_width, CV_32FC(datum_channels));
    for (int h = 0; h < datum_height; ++h) {
        float* ptr = cv_img.ptr<float>(h);
        int img_index = 0;
        for (int w = 0; w < datum_width; ++w) {
            for (int c = 0; c < datum_channels; ++c) {
                ptr[img_index++] = static_cast<float>(datum.float_data(img_index));
            }
        }
    }
}
return cv_img;

}

all code : http://lab.deepaivision.com/2017/06/opencv-mat-caffe-datum-datum-mat.html

Upvotes: 3

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