Saving images and then display them in a QLabel - c++

Question

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 :)

Answer 1

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.

Answer 2

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();
}
}