QT failed to load Image from Buffer

Question

My work Environment : Qt 5.8 MSVC2015 64bit, QT GraphicsView, Windows 7 64 bit

I am loading image from buffer (a demon process is going send a image buffer), but it failed to create image with buffer.

QFile file("D:\\2.png");
if (!file.open(QFile::ReadOnly))
    qDebug() << "Error failed to Open file";
QByteArray array = file.readAll();
array = array.toBase64();
QImage tempimage((uchar *)array.data(), 250, 250, QImage::Format_RGBX8888);
if (!tempimage.isNull()) {
      ///I always get this error
    qDebug() << "Error!!! failed to create a image!"; 
}

Any idea what I am missing here ?

your logic statement is wrong - you're saying if it's not null it's an error. Remove the `!` from `if (!tempimage.isNull())` — Steve Lorimer, May 16 '17 at 10:30
@ Steve Lorimer : thanks for correction. But My Image loaded as blur image. @ Tomaz array.data() is not a NULL value. — Sandip, May 16 '17 at 10:44
@Florent , I tried with image QImage::Format_BGR30. But I am still get disturbed image. — Sandip, May 16 '17 at 10:50
Have you tried the [`QImage` constructor which takes a path to a file](http://doc.qt.io/qt-5/qimage.html#QImage-8)? ie: no messing around with `QFile`, `QByteArray` etc — Steve Lorimer, May 16 '17 at 11:03
@Steve, Using QImage I able to load image successfully. But in my application another demon process is going send a image buffer. So I have to load image from buffer only. — Sandip, May 16 '17 at 11:12
Try use [`QImage::loadFromData`](http://doc.qt.io/qt-5/qimage.html#loadFromData-1) — Steve Lorimer, May 16 '17 at 11:17
I also suggest reading the guide: http://doc.qt.io/qt-5/qimage.html#reading-and-writing-image-files — Steve Lorimer, May 16 '17 at 11:17

score 0 · Answer 1 · answered May 16 '17 at 11:22

Why are you converting to base64?

Wait, where are you converting from PNG to an image plane?

Try bool QImage::loadFromData(const QByteArray &data, const char *format = Q_NULLPTR) to load the PNG instead of the CTor with the raw data.

If your wire format isn't PNG (and is in fact base64 encoded raw pixel data) then you want to convert FROM base64.

score 0 · Answer 2 · answered May 16 '17 at 11:39

Thanks for all suggestion & help. I fix my mistakes removed base64 conversion & loaded buffer using loadFromData with QByteArray reinterpret_cast:

Here is a final solution :

QFile file("D:\\2.png");
if (!file.open(QFile::ReadOnly))
    qDebug() << "Error failed to Open file";
QByteArray array = file.readAll();

 QImage tempimage;
 //// This very important to cast in below format, QByteArray don't work as arguments.
 tempimage.loadFromData(reinterpret_cast<const uchar *>(array.data()),array.size());
if (tempimage.isNull()) {
    qDebug() << "Error!!! failed to create a image!";
}

QT failed to load Image from Buffer

2 Answers2