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 ?