Help capturing an image

[John1123]

Hello,
I'm using multimedia to try and capture an image from my camera. I believe my connections are correct (they're similar to the example that is provided) but whenever I try to capture() a readyForCaptureChanged signal is emitted and isReadyForCapture changes from true to false. I made this a few months ago, I forgot which version I was on, and it was working fine, but recently I updated the components and I'm unable to capture an image.

[Axel Spoerl]

Since there is no code posted, we don't know what you are actually trying.
Maybe just read this, and if it doesn't solve your problem - post your code.

[John1123]

Thanks for getting back to me, unfortunately the link that you sent didn't help me. Here's the code that I'm using

from another file I'm calling getAvailableDevices(), then initDevice with a valid device index, then I'm setting the settings in captureSetting, and lastly I call captureFrame() where the image is supposed to be captured. The problem though is that whenever capture() is called readyForCapture is called again but ready is set to false.

VideoCapture::VideoCapture(QImage *image)
{
savedImage = image;
}

void VideoCapture::getAvailableDevices()
{
m_devices = QMediaDevices::videoInputs();
}

void VideoCapture::initDevice(const int deviceIdx )
{
int cnt = 0;

for (const QCameraDevice &cameraDevice : m_devices)
{
    qDebug() << cnt << ". " << cameraDevice.description();

    if(cameraDevice.isNull())
    {
        qDebug() << "\t"<< cnt++ << " is null\n";
    }
}
qDebug() << "Initializing device " << deviceIdx << " for capturing an image" << Qt::endl;

/*Initialize a capture device*/
m_targetDevice.reset(new QCamera(m_devices[deviceIdx]));
m_captureSession.setCamera(m_targetDevice.data());

/*Initialize a QImageCapture instance*/
m_capture = new QImageCapture;
m_captureSession.setImageCapture(m_capture);

/*Connections for updating the camera*/
connect(m_targetDevice.data(), &QCamera::activeChanged, this, &VideoCapture::updateCameraActive, Qt::DirectConnection);
connect(m_targetDevice.data(), &QCamera::errorOccurred, this, &VideoCapture::cameraError, Qt::DirectConnection);

/*Conenctions for capturing an image*/
connect(m_capture, &QImageCapture::readyForCaptureChanged, this, &VideoCapture::readyForCapture, Qt::DirectConnection);
connect(m_capture, &QImageCapture::imageCaptured, this, &VideoCapture::imageCaptured, Qt::DirectConnection);
connect(m_capture, &QImageCapture::errorOccurred, this, &VideoCapture::captureError, Qt::DirectConnection);

};

void VideoCapture::updateCameraActive(bool ready)
{
if (ready)
{
qDebug() << "Camera is active ";
}
else
{
qDebug() << "Camera is not active";
}
}

void VideoCapture::captureSetting(int width, int height)
{
m_capture->setFileFormat(QImageCapture::PNG);
m_capture->setQuality(QImageCapture::VeryHighQuality);
m_capture->setResolution(width, height);
}

void VideoCapture::captureFrame()
{
m_targetDevice->start();
updateCameraActive(m_targetDevice->isActive());
checkReadyForCapture();
readyForCapture(m_capture->isReadyForCapture());
}

void VideoCapture::imageCaptured(int requestId, const QImage &img)
{
Q_UNUSED(requestId);
Q_UNUSED(img);
qDebug() << "Image Captured!!";
*savedImage = img.copy();
m_targetDevice->stop();
}

void VideoCapture::readyForCapture(bool ready)
{
if(ready)
{
qDebug() << "Capture ready";
m_capture->capture();
}
else
{
qDebug() << "Capture not ready";
}
}

void VideoCapture::captureError(int id, const QImageCapture::Error error, const QString &errorString)
{
Q_UNUSED(id);
Q_UNUSED(error);
qDebug() << "Capture Error: " << errorString;
m_targetDevice->stop();
}

void VideoCapture::cameraError()
{
if (m_targetDevice->error() != QCamera::NoError)
{
qDebug() << "Camera error: " << m_targetDevice->errorString();
}
}

void VideoCapture::checkReadyForCapture()
{
QString boolStr = m_capture->isReadyForCapture() ? "True" : "False";
qDebug() << "isReadyForCapture: " << boolStr;
}

[SGaist]

Hi,

There several strange (as in wrong) stuff in your code:

• Why are you forcing the connection type to be DirectConnection ? There's rarely a need to specify the type of connection.
• Why is savedImage a pointer rather than a QImage object ? There's usually no need for that

Additional questions:

• Which version of Qt ?
• On which OS ?

[John1123]

For DirectConnection, I added that because I thought I needed it; Ill take it off. savedImage is used in the file that calls the VideoCapture functions. I'm running QT on 6.6.3 and I'm on windows

[SGaist]

You should rather emit the new image from your VideoCapture class rather than fiddling with a variable that it should not know about.

[John1123]

Ok, ill look into emitting the image that it captures, but I still have the problem where capture() wont capture an image

[SGaist]

Did you try to save the image in a file to see how it looks ?

[John1123]

An image can't be captured in the first place, whenever I call capture it redirects to readyForCapture and isReadyForCapture changes from true to false. This also applies to captureToFile()

[SGaist]

Which version of Qt are you using ?
On which OS ?
With which device ?

[John1123]

I'm running QT on 6.6.3, I'm on windows, and I'm using my webcam

[SGaist]

Which version of Windows ?
What is the model of your webcam ?

[John1123]

my webcam is a Logi C615 HD WebCam, and im on windows 10

[SGaist]

Can you check again with 6.7 ?

[John1123]

I've checked again in 6.7 and it still doesn't work.

[SGaist]

Ok, then can you switch the backend to use the native rather than ffmpeg ?

[John1123]

How would I do that?

[SGaist]

It's described here.

[John1123]

So I've tried it, and now isReadyForCapture doesn't change to false after capture() is called but it still doesn't capture an image

[SGaist]

Can you provide a minimal compilable example that shows this behaviour ?