Converting cv::mat to QImage - c++

like the title says I am trying to convert a cv::mat to a QImage. What I am doing is using the equalizeHist() function on the mat and then converting it to a QImage to display in widget window in Qt. I know the mat works and loads the image correctly because the equalized image will show in the new window with imshow(), however when converting this mat to a QImage, I can not get it to display in the window. I believe the problem is with the conversion from the mat to QImage but cant find the issue. Below is a part of my code snippet.
Mat image2= imread(directoryImage1.toStdString(),0);
//cv::cvtColor(image2,image2,COLOR_BGR2GRAY);
Mat histEquImg;
equalizeHist(image2,histEquImg);
imshow("Histogram Equalized Image 2", histEquImg);
//QImage img=QImage((uchar*) histEquImg.data, histEquImg.cols, histEquImg.rows, histEquImg.step, QImage::Format_ARGB32);
imageObject= new QImage((uchar*) histEquImg.data, histEquImg.cols, histEquImg.rows, histEquImg.step, QImage::Format_RGB888);
image = QPixmap::fromImage(*imageObject);
scene=new QGraphicsScene(this); //create a frame for image 2
scene->addPixmap(image); //put image 1 inside of the frame
ui->graphicsView_4->setScene(scene); //put the frame, which contains image 3, to the GUI
ui->graphicsView_4->fitInView(scene->sceneRect(),Qt::KeepAspectRatio); //keep the dimension ratio of image 3
No errors occur and the program doesnt crash.
Thanks in advance.

Your problem is the conversion of the QImage to cv::Mat, when using the flag 0 in cv::imread implies the reading is grayscale, and you are using the conversion with the format QImage::Format_RGB888. I use the following function to make the conversion of cv::Mat to QImage:
static QImage MatToQImage(const cv::Mat& mat)
{
// 8-bits unsigned, NO. OF CHANNELS=1
if(mat.type()==CV_8UC1)
{
// Set the color table (used to translate colour indexes to qRgb values)
QVector<QRgb> colorTable;
for (int i=0; i<256; i++)
colorTable.push_back(qRgb(i,i,i));
// Copy input Mat
const uchar *qImageBuffer = (const uchar*)mat.data;
// Create QImage with same dimensions as input Mat
QImage img(qImageBuffer, mat.cols, mat.rows, mat.step, QImage::Format_Indexed8);
img.setColorTable(colorTable);
return img;
}
// 8-bits unsigned, NO. OF CHANNELS=3
if(mat.type()==CV_8UC3)
{
// Copy input Mat
const uchar *qImageBuffer = (const uchar*)mat.data;
// Create QImage with same dimensions as input Mat
QImage img(qImageBuffer, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);
return img.rgbSwapped();
}
return QImage();
}
After that I see that you have misconceptions of how QGraphicsView and QGraphicsScene work when commenting: put the frame, which contains image 3, to the GUI, with ui->graphicsView_4->setScene(scene); you are not setting a frame but a scene, and the scene should only be set once and preferably in the constructor.
// constructor
scene = new QGraphicsScene(this);
ui->graphicsView->setScene(scene);
So when you want to load the image just use the scene:
cv::Mat image= cv::imread(filename.toStdString(), CV_LOAD_IMAGE_GRAYSCALE);
cv::Mat histEquImg;
equalizeHist(image, histEquImg);
QImage qimage = MatToQImage(histEquImg);
QPixmap pixmap = QPixmap::fromImage(qimage);
scene->addPixmap(pixmap);
ui->graphicsView->fitInView(scene->sceneRect(), Qt::KeepAspectRatio);
The complete example can be found in the following link.

Related

Display Qbytearray as Image in QT 5.12.9 version

I am reading the QByteArray using QTcpSocket and converting the array into the cvMat image. to display the image using imshow().but i am getting gray image.
code is as follows.
//array ->QBytearray (received from socket)
cv::Mat img,img1;
img.cols=320;
img.rows=240;
img = cv::Mat(240,320, CV_8UC1,array.data());
cv::cvtColor(img, img, CV_GRAY2RGB); //
cv::imshow("image display",img);
cv::waitKey(5000);
after cvtColour() function also its not converting into colour image.
Thanks in advance.
This is the way to modify channels separately:
img = cv::Mat(240,320, CV_8UC1,array.data());
cv::Mat img1;
cv::divide(img,cv::Scalar(2),img1);
std::vector<cv::Mat> channels;
channels.push_back(img);
channels.push_back(img1);
channels.push_back(img);
cv::merge(channels, img);
cv::imshow("image display",img);
cv::waitKey(5000);

Saving images and then display them in a QLabel

I'm currently building a Qt application that using some camera.
In this application the uses capture images, and then they are automatically saved in a specific folder. Everything works great.
Now, when the "library" button is clicked, I want to read all the images (JPEG files) and display all the images that were taken one by one in a QLabel.
I couldn't find any tutorials for this, only found tutorials and uses the argv argument which is no good for me, because in my application the user may capture images and then display them in the same run.
How can read the files list and display it?
Thank you very much :)
If you have a single QLabel then you have to join the images together a single one. I find easier to display a list of QLabels:
auto layout = new QVBoxLayout();
Q_FOREACH (auto imageName, listOfImages) {
QPixmap pixmap(dirPath + "/" + imageName);
if (!pixmap.isNull()) {
auto label = new QLabel();
label->setPixmap(pixmap);
layout->addWidget(label);
}
}
a_wdiget_where_to_show_images->setLayout(layout);
The last line will depend on when do you want to place the labels. I suggest some widget with a scroll bar.
Now, you want to read all the images from a directory (the listOfImages variable above). If you don't have it:
const auto listOfImages = QDir(dirPath).entryList(QStringList("*.jpg"), QDir::Files);
You may have layout problems if your images are too big. In that case you should scale them if they are bigger than a given size. Take a look at QPixmap::scaled or QPixmap::scaledToWidth. Also, if image quality is important, specify Qt::SmoothTransformation as the transformation mode.
You can use opencv library to read all images in a directory.
vector<String> filenames; // notice here that we are using the Opencv's embedded "String" class
String folder = "Deri-45x45/"; // again we are using the Opencv's embedded "String" class
float sayi = 0;
glob(folder, filenames); // new function that does the job ;-)
float toplam = 0;
for (size_t i = 0; i < filenames.size(); ++i)
{
Mat img = imread(filenames[i],0);
//Display img in QLabel
QImage imgIn = putImage(img);
imgIn = imgIn.scaled(ui->label_15->width(), ui->label_15->height(),Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
ui->label_15->setPixmap(QPixmap::fromImage(imgIn));
}
In order to convert Mat type to QImage, we use putImage function:
QImage putImage(const Mat& mat)
{
// 8-bits unsigned, NO. OF CHANNELS=1
if (mat.type() == CV_8UC1)
{
// Set the color table (used to translate colour indexes to qRgb values)
QVector<QRgb> colorTable;
for (int i = 0; i < 256; i++)
colorTable.push_back(qRgb(i, i, i));
// Copy input Mat
const uchar *qImageBuffer = (const uchar*)mat.data;
// Create QImage with same dimensions as input Mat
QImage img(qImageBuffer, mat.cols, mat.rows, mat.step, QImage::Format_Indexed8);
img.setColorTable(colorTable);
return img;
}
// 8-bits unsigned, NO. OF CHANNELS=3
if (mat.type() == CV_8UC3)
{
// Copy input Mat
const uchar *qImageBuffer = (const uchar*)mat.data;
// Create QImage with same dimensions as input Mat
QImage img(qImageBuffer, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);
return img.rgbSwapped();
}
else
{
qDebug() << "ERROR: Mat could not be converted to QImage.";
return QImage();
}
}

convert Qimage to cvMat 64FC3 format

i have searched a lot on the internet but i have only found how to convert Qimage to RGB format, i want to convert an Qimage to cv mat format CV_64FC3.
i have really bad results when i work with CV_8UC3
here is my code :
QImage myImage;
myImage.load("C://images//PolarImage300915163358.bmp");
QLabel myLabel;
myLabel.setPixmap(QPixmap::fromImage(myImage));
//myLabel.show();
cv::Mat image1 = QImage2Mat(myImage);
Mat img;
image1.convertTo(img, CV_64FC3, 1.0 / 255.0);
and here is the function that i used :
cv::Mat QImage2Mat(QImage const& src)
{
cv::Mat tmp(src.height(),src.width(),CV_8UC3,(uchar*)src.bits(),src.bytesPerLine());
cv::Mat result; // deep copy just in case (my lack of knowledge with open cv)
cvtColor(tmp, result,CV_BGR2RGB);
return result;
}
please help me i m new to both opencv and Qt
Not sure what you mean with bad results, but you are assuming that QImage also loads the image as OpenCV (BGR). In the documentation it tells you that they use ARGB.
So, knowing this you have 2 options:
Convert to QImage::Format_RGB888 the Qimage using the function convertToFormat and then this line cvtColor(tmp, result,CV_BGR2RGB); is not needed, since it will be already in RGB.
Use CV_8UC4 when creating the cv::Mat and then drop the first channel (channel alpha) using either split and join or mixchannels.
i have found what was going wrong, in fact, Qimage has a fourth channel for alpha so when you read the Qimage data you need to put it in CV_8UC4
here is the code :
Mat QImage2Mat(const QImage& src) {
cv::Mat mat = cv::Mat(src.height(), src.width(), CV_8UC4, (uchar*)src.bits(), src.bytesPerLine());
cv::Mat result = cv::Mat(mat.rows, mat.cols, CV_8UC3 );
int from_to[] = { 0,0, 1,1, 2,2 };
cv::mixChannels( &mat, 1, &result, 1, from_to, 3 );
return result;
}

Qt OpenCV - SIGSEGV when displaying transformed frames

I have an app that has to pull frames from video, transform one a little, transform one a lot, and simultaneously display them in GUI. In a worker thread, there's an OpenCV loop:
while(1) {
cv::VideoCapture kalibrowanyPlik;
kalibrowanyPlik.open(kalibracja.toStdString()); //open file from url
int maxFrames = kalibrowanyPlik.get(CV_CAP_PROP_FRAME_COUNT);
for(int i=0; i<maxFrames; i++) //I thought it crashed when finished reading the first time around
{
cv::Mat frame;
cv::Mat gray;
cv::Mat color;
kalibrowanyPlik.read(frame);
cv::cvtColor(frame, gray, CV_BGR2GRAY);
cv::cvtColor(frame, color, CV_BGR2RGB);
QImage image((uchar*)color.data, color.cols, color.rows,QImage::Format_RGB888);
QImage processedImage((uchar*)gray.data, gray.cols, gray.rows,QImage::Format_Indexed8);
emit progressChanged(image, processedImage);
QThread::msleep(50);
}
}
And this is how frames are placed in GUI
void MainWindow::onProgressChagned(QImage image, QImage processedImage) {
QPixmap processed = QPixmap::fromImage(processedImage);
processed = processed.scaledToHeight(379);
ui->labelHsv->clear();
ui->labelHsv->setPixmap(processed);
QPixmap original = QPixmap::fromImage(image); //debug points SIGSEGV here
original = original.scaledToHeight(379);
ui->labelKalibracja->clear();
ui->labelKalibracja->setPixmap(original);
}
The RGB image always crashes, grayscale image never crashes (tested). Why is the RGB image crashing?
edit: I've just discovered that if I change msleep(50) to msleep(100) it executes perfectly. But I don't want that. I need at least 25 frames per second, 10 is not acceptable... why would that cause a SIGSEGV
Standard issue. Problem is memory management!
See my other answer. In comments there is a good link.
So in your code QImage doesn't copy and doesn't take ownership of memory of matrix. And later on when matrix is destroyed and QImage tries access this memory (QImage is copied by creating shallow copy) you have a segfault.
Here is a code form this link (I've tweak it a bit), for some reason this site has some administration issues (some quota exceeded), that is why I'm pasting it here.
inline QImage cvMatToQImage( const cv::Mat &inMat )
{
switch ( inMat.type() )
{
// 8-bit, 4 channel
case CV_8UC4:
{
QImage image( inMat.data, inMat.cols, inMat.rows, inMat.step, QImage::Format_RGB32 );
QImage copy(image);
copy.bits(); //enforce deep copy
return copy;
}
// 8-bit, 3 channel
case CV_8UC3:
{
QImage image( inMat.data, inMat.cols, inMat.rows, inMat.step, QImage::Format_RGB888 );
return image.rgbSwapped();
}
// 8-bit, 1 channel
case CV_8UC1:
{
static QVector<QRgb> sColorTable;
// only create our color table once
if ( sColorTable.isEmpty() )
{
for ( int i = 0; i < 256; ++i )
sColorTable.push_back( qRgb( i, i, i ) );
}
QImage image( inMat.data, inMat.cols, inMat.rows, inMat.step, QImage::Format_Indexed8 );
image.setColorTable( sColorTable );
QImage copy(image);
copy.bits(); //enforce deep copy
return copy;
}
default:
qWarning() << "ASM::cvMatToQImage() - cv::Mat image type not handled in switch:" << inMat.type();
break;
}
return QImage();
}
Your code should utilize this functions like that:
while(1) {
cv::VideoCapture kalibrowanyPlik;
kalibrowanyPlik.open(kalibracja.toStdString()); //open file from url
int maxFrames = kalibrowanyPlik.get(CV_CAP_PROP_FRAME_COUNT);
for(int i=0; i<maxFrames; i++) //I thought it crashed when finished reading the first time around
{
cv::Mat frame;
cv::Mat gray;
kalibrowanyPlik.read(frame);
cv::cvtColor(frame, gray, CV_BGR2GRAY);
QImage image(cvMatToQImage(frame));
QImage processedImage(cvMatToQImage(gray));
emit progressChanged(image, processedImage);
QThread::msleep(10); // this is bad see comments below
}
}
Use of msleep is in 95% cases bad! Remove this loop and create slot which will be invoked by signal from QTimer.
Another solution will be to use a timer :
void ??::timerEvent(QTimerEvent*){
if(kalibrowanssky.isOpened())
cv::Mat frame;
cv::Mat gray;
cv::Mat color;
kalibrowanyPlik.read(frame);
cv::cvtColor(frame, gray, CV_BGR2GRAY);
cv::cvtColor(frame, color, CV_BGR2RGB);
ui->labelHsv->setPixmap(QPixmap::fromImage(Mat2QImage(color)));
ui->labelKalibracja->setPixmap(QPixmap::fromImage(Mat2QImage(gray)));
}
In your main :
cv::VideoCapture kalibrowanyPlik;
startTimer(1000/25); // 25 frames by second
And the function Mat2QImage (I found it here : how to convert an opencv cv::Mat to qimage) :
QImage ??::Mat2QImage(cv::Mat const& src) {
cv::Mat temp;
cvtColor(src, temp,CV_BGR2RGB);
QImage dest((const uchar *) temp.data, temp.cols, temp.rows, temp.step, QImage::Format_RGB888);
dest.bits();
return dest;
}

How to convert QImage to opencv Mat

I have searched on the internet but I cannot find a method of converting a QImage(or QPixmap) to a OpenCV Mat. How would I do this?.
Any help is appreciated.
If the QImage will still exist, and you just need to perform a quick operation on it then you can construct a cv::Mat using the QImage memory:
cv::Mat mat(image.height(), image.width(), CV_8UC3, (cv::Scalar*)image.scanLine(0));
This assumes that the QImage is 3-channels, ie RGB888.
If the QImage is going away then you need to copy the data, see Qimage to cv::Mat convertion strange behaviour.
If QImage is Format_ARGB32_Premultiplied (the preferred format) then you will need to convert each pixel to OpenCV's BGR layout. The cv::cvtcolor() function can convert ARGB to RGB in the latest versions.
Or you can use QImage::convertToFormat() to convert to RGB before copying the data.
One year after you issued this question there've been great answers on the internet:
Convert between cv::mat and Qimage correctly
Converting Between cv::Mat and QImage or QPixmap
But the way I see it, if you're working with Qt and OpenCV at the same time then type QImage is probably just for displaying, that case you might want to use QPixmap since it's optimized for displaying. So this is what I do:
Load image as cv::Mat, if you'd like to display the image, convert to QPixmap using the non-copy method introduced in the second article.
Do your image processing in cv::Mat.
Any time during the workflow you can call upon something like Mat2QPixmap() to get realtime result.
Never convert QPixmap to cv::Mat, there's no sense doing it considering the purpose of each type.
The answer to this with Qt 5.11 (and probably some earlier versions):
cv::Mat mat(image.height(), image.width(),CV_8UC3, image.bits());
// image.scanline() does not exist,
//and height/width is interchanged for a matrix
Again the QImage is assumed to be RGB888 (ie QImage::Format_RGB888)
My attempt in OpenCV 3.1+ style code:
void qimage_to_mat(const QImage& image, cv::OutputArray out) {
switch(image.format()) {
case QImage::Format_Invalid:
{
cv::Mat empty;
empty.copyTo(out);
break;
}
case QImage::Format_RGB32:
{
cv::Mat view(image.height(),image.width(),CV_8UC4,(void *)image.constBits(),image.bytesPerLine());
view.copyTo(out);
break;
}
case QImage::Format_RGB888:
{
cv::Mat view(image.height(),image.width(),CV_8UC3,(void *)image.constBits(),image.bytesPerLine());
cvtColor(view, out, cv::COLOR_RGB2BGR);
break;
}
default:
{
QImage conv = image.convertToFormat(QImage::Format_ARGB32);
cv::Mat view(conv.height(),conv.width(),CV_8UC4,(void *)conv.constBits(),conv.bytesPerLine());
view.copyTo(out);
break;
}
}
}
void mat_to_qimage(cv::InputArray image, QImage& out)
{
switch(image.type())
{
case CV_8UC4:
{
cv::Mat view(image.getMat());
QImage view2(view.data, view.cols, view.rows, view.step[0], QImage::Format_ARGB32);
out = view2.copy();
break;
}
case CV_8UC3:
{
cv::Mat mat;
cvtColor(image, mat, cv::COLOR_BGR2BGRA); //COLOR_BGR2RGB doesn't behave so use RGBA
QImage view(mat.data, mat.cols, mat.rows, mat.step[0], QImage::Format_ARGB32);
out = view.copy();
break;
}
case CV_8UC1:
{
cv::Mat mat;
cvtColor(image, mat, cv::COLOR_GRAY2BGRA);
QImage view(mat.data, mat.cols, mat.rows, mat.step[0], QImage::Format_ARGB32);
out = view.copy();
break;
}
default:
{
throw invalid_argument("Image format not supported");
break;
}
}
}
cv::Mat to_cvmat(QImage img)
{
img = img.convertToFormat(QImage::Format_RGB888, Qt::ColorOnly).rgbSwapped();
return cv::Mat(img.height(), img.width(), CV_8UC3, img.bits(), img.bytesPerLine()).clone();
}