Hi I am trying to draw a contour to a base64 encoded qbytearray by converting it to cv mat and revert it back to qbyte array to display on qml.
While the first part is working correclty, I can't seem to convert the cv mat to qbytearray back properly
the code that I am using now is
cv::Mat final_img;
cv::Mat dst;
cv::resize(final_img, final_img, final_img.size());
cv::cvtColor(final_img, dst, cv::COLOR_BGR2BGRA);
QByteArray data = QByteArray::fromRawData(reinterpret_cast<char*>(dst.data), 592355);
decoded_image = "data:image/jpeg;base64,";
decoded_image.append(QString::fromLatin1(data.toBase64().data()));
I get a correct format of base64encoded bytearray but gets the following error
Unsupported image format
Any help will be appreciated! Thanks
Related
// `s` is the webots's rangefinder
auto buffer = (float*)s->getRangeImage();
cv::Mat img(cv::Size(width, height), CV_32FC1, buffer); // image data is float*
// check and success.
// imshow("pic", img);
// cvWaitKey(0);
// encode:
std::vector<uchar> newBuffer;
cv::imencode(".jpg", img, newBuffer);
// decode
auto img_decode = cv::imdecode(newBuffer, cv::IMREAD_UNCHANGED);
// fail and get a black image
imshow("pic", img_decode);
cvWaitKey(0);
I have try to use other params in function cv::imdecode like cv::IMREAD_ANYDEPTH but fail. I am searching for a long time on net. But no use. Please help or try to give some ideas how to achieve this.
If your data is real, i.e. floating point, and single channel, you could try writing to a PFM or TIFF format image which will support that data type.
As #wohlstad mentions in the comments, JPEG is uint8 so only supports integers in the range 0..255.
If I have an opencv image that I read from a png file like this:
cv::Mat img = cv::imread("/to/path/test.png");
how do I get that image in bytes? I know using img.data returns an unsigned char* but that is not what I need. Any suggestions?
If I got your question right, you want, for example, a 250*250 image to return a 250*250 matrix so I would suggest using grey-scale instead of BGR
imgData = cv2.imread(path, 0)
I believe this is written in C++ like this
cv::Mat img = cv::imread(file_name);//It returns a matrix object
cv::Mat graymat;
cvtColor(img, graymat,cv::COLOR_BGR2GRAY);
I've created a filter extending QAbstractVideoFilter and
QVideoFilterRunnable and I've overrided the
QVideoFrame run(QVideoFrame* input, const QVideoSurfaceFormat &surfaceFormat, RunFlags flags)`
method
The problem is that QVideoFrame format is Format_YUV420P and has no handle. I need to convert it into a CV_8UC1 in order to use OpenCV algorithms.
Which is the best way to accomplish this?
First you need to create a cv::Mat which has an API for initializing using data pointer as:
cv::Mat img = cv::Mat(rows, cols, CV_8UC3, input.data/*Change this to point the first element of array containing the YUV color info*/)
Now since the img is initialized with YUV color data, you may use various cvtColor modes to convert the YUV mat to other formats, for converting it to gray-scale you may try:
cv::Mat gray;
cv::cvtColor(img, gray, cv::COLOR_YUV2GRAY_I420);
I want to load an image in c++ opencv that comes from a postgresql database.
The image, jpg extension, is stored as a binary data (bytea type) in the base, that I can access thanks to libpqxx.
The problem is that I do not know how to convert the data into a cv::Mat instance. With a regular image I could use imread('myImage.jpg', ...), but in this case I cannot even load the database image in the data attribute of Mat because it is jpeg and not bmp.
Any idea ? Is there some opencv method I could use that could understand directly the binary data and convert it to the appropriate structure ? the imdecode() functions seems to be used for bitmap datas.
edit : Berak, using a vector the imdecode function returns null Matrice What happens "If the buffer is too short or contains invalid data, the empty matrix/image is returned." Here is the code :
pqxx::result r=bdd::requete("SELECT image FROM lrad.img WHERE id=3",1);//returns the bytea image in r[0]["image"]
const char* buffer=r[0]["image"].c_str();
vector<uchar>::size_type size = strlen((const char*)buffer);
vector<uchar> jpgbytes(buffer, buffer+size);
Mat img = imdecode(jpgbytes, CV_LOAD_IMAGE_COLOR);
//jpgbytes.size()=1416562 img.size()=[0 x 0]
What am I missing ?
still, use imdecode . it can handle png,jpg,bmp,ppm,webp,jp2,exr, but no gif.
vector<uchar> jpgbytes; // from your db
Mat img = imdecode(jpgbytes);
(you should do the same for bmp or any other supported formats, don't mess with Mat's raw data pointers!)
Ok I have the process to convert a bytea data to a cv::Mat, here is the code.
inline int dec(uchar x){ //convert uchar to int
if (x>='0'&&x<='9') return (x-'0');
else if (x>='a'&&x<='f') return (x-'a'+10);
else if (x>='A'&&x<='F') return (x-'A'+10);
return 0;
}
cv::Mat bytea2Mat(const pqxx::result::field& f){
const char* buffer=f.c_str();
vector<uchar>::size_type size = strlen((const char*)buffer);
vector<uchar> jpgbytes(size/2-1);
for (size_t i=0; i!=size/2-1;i++) {
jpgbytes[i]=(dec(buffer[2*(i+1)])<<4)+dec(buffer[2*(i+1)+1]);
}
cout <<size/2<<";"<<jpgbytes.size()<<endl;
return imdecode(jpgbytes, CV_LOAD_IMAGE_COLOR);
}
The bytea output is encrypted as a char* looking like "\x41204230", for an original input string of "a b0" in hexa form. (the \x may not be present according to the data input)
to get the original data you have to calculate the original input from the two char, ('4','1'= 0x41=65). The vector is half the size of the char*.
I'm trying to show LiveView image in real time. I use EDSDK 2.14 + Qt5 + opencv+mingw32 under Windows. I'm not very sophisticated in image processing so now I have the following problem. I use example from Canon EDSDK and all was ok until this part of code:
//
// Display image
//
I googled a lot of examples but all of them was written on C# or MFC or VB. Also I found advise to use libjpegTurbo for decompressing image and then showing it using opencv. I tried to use libjpegTurbo but failed to undestand what to do :(. Maybe somebody here have code example of the conversion LiveView stream to opencv Mat or QImage (because I use Qt)?
Here is what worked for me after following the SAMPLE 10 from the Canon EDSDK Reference. It's a starting point for a more robust solution.
In the downloadEvfData function, I replaced the "Display Image" part by the code bellow:
unsigned char *data = NULL;
EdsUInt32 size = 0;
EdsSize coords ;
// get image coordinates
EdsGetPropertyData(evfImage, kEdsPropsID_Evf_CoordinateSystem, 0, sizeof(coords), &coords);
// get buffer pointer and size
EdsGetPointer(stream, (EdsVoid**)&data);
EdsGetLenth(stream, &size);
//
// release stream and evfImage
//
// create mat object
Mat img(coords.height, coords.width, CV_8U, data);
image = imdecode(img, CV_LOAD_IMAGE_COLOR);
I've also changed the function signature:
EdsError downloadEvfData(EdsCameraRef camera, Mat& image)
And in the main function:
Mat image;
namedWindow("main", WINDOW_NORMAL);
startLiveView(camera);
for(;;) {
dowloadEvfData(camera, image);
imshow("main", image);
if (waitkey(10) >= 0);
break;
}
Based on the Canon EDSDKs example, you may append your EdsStreamRef 'stream' data with its correct length into a QByteArray. Then, use for example the following to parse the raw data from the QByteArray as a JPG into a new QImage:
QImage my_image = QImage::fromData(limagedata,"JPG"); Once it's in a QImage you can convert it into a OpenCV cv::Mat (see How to convert QImage to opencv Mat)
Well it depends on the format of the liveview-stream.
There must be some kind of delimiter in it and you need then to convert each image and update your QImage with it.
Check out this tutorial for more information: Canon EDSDK Tutorial in C#
QImage img = QImage::fromData(data, length, "JPG");
m_image = QImageToMat(img);
// -----------------------------------------
cv::Mat MainWindow::QImageToMat(QImage& src)
{
cv::Mat tmp(src.height(),src.width(),CV_8UC4,(uchar*)src.bits(),src.bytesPerLine());
cv::Mat result = tmp.clone();
return result;
}
// -------------------------
void MainWindow::ShowVideo()
{
namedWindow("yunhu",WINDOW_NORMAL);
while(1)
{
requestLiveViewImage();
if(m_image.data != NULL)
{
imshow("yunhu", m_image);
cvWaitKey(50);
}
}
}