How to get a picture from QString in Qt

[Mikeeeeee]

Hi!
So I translate the picture into a QString :

QString AppCore::getImage(QString addressFile)
{
    QImage myImage(addressFile);

    QByteArray bArray;
    QBuffer buffer(&bArray);
    buffer.open(QIODevice::WriteOnly);
    myImage.save(&buffer, "JPEG");

    QString image("data:image/jpg;base64,");
    image.append(QString::fromLatin1(bArray.toBase64().data()));

    //qDebug()<<"bArray.size() : "<<bArray.size();
    QPixmap pixamp1;
    QByteArray bArray2;
    //bArray2 = QByteArray::fromHex(image.toLocal8Bit());
    /*bArray2.append(image);
    pixamp1.loadFromData(bArray2,nullptr,Qt::AutoColor);
    qDebug()<<"pixamp1.size() : "<<pixamp1.size();*/

    return image;
}

Array b Array is translated into a picture, but to perform the transformation with the QString in image does not work.
Please tell me how this can be done?

[Christian Ehrlicher]

So where/how do you display this base64 encoded image?

[Mikeeeeee]

I do not display it anywhere yet, just transfer it to the server. But not in the program can transfer QString in the picture

[Mikeeeeee]

Just tried to string so

QString imageString = QString::fromStdString(bArray.toStdString());

[Christian Ehrlicher]

Can you please explain what you're really trying to do...

[Mikeeeeee]

I need to translate the picture into Qstring, transfer to another device and again translate into a picture.

[Christian Ehrlicher]

And how do you transfer the data?

[Mikeeeeee]

I use TcpSocket

[Gojir4]

@mikeeeeee Hi,

I think it's easier if you use QDataStream.
I never tested but it seems quite straightforward

Write

QDataStream out(&socket);   // serialize the data 
out << myImage;             // serialize an image

Read

QDataStream in(&socket);    // read the data serialized from the socket
QImage myImage;
in >> myImage;              // extract image

[aha_1980]

@mikeeeeee said in How to get a picture from QString in Qt:

I use TcpSocket

Then you don't need QString. You need QByteArray, probably QDataStream as @Gojir4 pointed out.

QString imageString = QString::fromStdString(bArray.toStdString());

Sorry, but never do that!

QString imageString = QString::fromUtf8(bArray); is most often correct, sometimes fromLatin1() or fromLocal8Bit() might be needed too.

But as said, your problem cannot be solved with QString.

Regards

[Mikeeeeee]

But I pass the picture to json , and with the picture I pass additional information to the server. So I need a QString.

[SGaist]

Hi,

As already explained by my fellows, use QByteArray. QString is for string manipulation, it's not what you are doing. You are sending data through network. Therefore you are creating a base64 QByteArray that represent your image's binary data. There's no need for any QString in between.

[Mikeeeeee]

But as I write in Qbytearray json?
And why this doesn't it work:

    /*QString imageString = QString::fromLocal8Bit(bArray);
    bArray2 = QByteArray::fromHex(imageString.toLocal8Bit());*/
    QString imageString = QString::fromLatin1(bArray);
    bArray2 = QByteArray::fromHex(imageString.toLatin1());
    if (bArray != bArray2) {qDebug()<<"bArray != bArray2";}
    else {"bArray == bArray2";}

debug return: bArray != bArray2

[SGaist]

At one point you are encoding in base64 and the other you are decoding from hex. These are two completely different things.

Also, QString does a conversion to UTF16. So again, the fact that JSON contains text doesn't mean that you need to use QString.

[Mikeeeeee]

But as a json, you can write a qbytearray? And how to write the qbytearray to a string and then again in qbytearray?

[SGaist]

Take a look at QJsonDocument, no QString there.

[Mikeeeeee]

But I can't write qbytearray to json. And how to write the qbytearray to a string and then again in qbytearray?

[SGaist]

You have to understand that it's the QByteArray that will contain the JSON data.

Again, read the documentation of QJsonDocument, the related classes and example code.

[Mikeeeeee]

I read the documentation, it does not specify the ability to add QByteArray to json. So how can I translate QByteArray to Qstring and then to QByteArray?

[aha_1980]

@mikeeeeee Then you need to read more carefully.

https://doc.qt.io/qt-5/qjsondocument.html#toJson
https://doc.qt.io/qt-5/qjsondocument.html#fromJson

[Mikeeeeee]

I don't see how it will help to write QByteArray to json. Again, I can write Qstring to json. It remains only to learn how to safely translate from Qstring to QByteArray .

[J.Hilk]

@mikeeeeee do you actually want a qbytearray as a value to a key inside your son file ?

[Mikeeeeee]

So it turns QString into a picture to translate

QString AppCore::getImage(QString addressFile)
{
    QImage myImage(addressFile);

    QByteArray bArray;
    QBuffer buffer(&bArray);
    buffer.open(QIODevice::WriteOnly);
    myImage.save(&buffer, "JPEG");

    QString image("data:image/jpg;base64,");
    image.append(QString::fromLatin1(bArray.toBase64().data()));

    QImage testImage(image);
    qDebug()<<"myImage.size() : "<<myImage.size();

    return image;
}