How to convert QImage to QByteArray?

Try this:

QByteArray arr = QByteArray::fromRawData((const char*)img.bits(), img.byteCount());

You could do this:

QImage img_enrll;
QByteArray arr;
QBuffer buffer(&arr);
buffer.open(QIODevice::WriteOnly);
img_enrll.save(&buffer, "yourformat");

Having written that, if you need this for serialization, you are better of with QDataStream.