QCamera has strange blue tint

SolaVitae

Currently, my QCamera/viewfinder has a very strange blue tint, as seen here

alt text

This is the original image

alt text

I'm using a virtual webcam for testing, but the tint issue is the same on my actual webcam as well. Using the built-in windows Camera app has no blue tint, and the image appears fine. I'm using the built-in QCamera example from creator as well for testing

Kent-Dorfman

yes, it does. Is there a question in there?

Have you verified that the color model output of the camera is what Qt thinks it is? is it JPG or one of the many YUV image formats?

SolaVitae

@Kent-Dorfman
I guess the question would be how do I get rid of it; would the expected image format be an issue even with a virtual webcam?

Kent-Dorfman

oh...virtual webcam problem with ALL images, or just ones captured from the real camera?

SolaVitae

@Kent-Dorfman

The virtual webcam just emulates a webcam and let's you show something like your desktop, or a still image (it shows up as a separate device on the device list) I'm only using it to see if the blue tint was an issue with my actual webcam, but both my actual webcam and the virtual webcam both have the blue tint, but only in QT, as images captured outside of QT look perfectly normal

Kent-Dorfman

I understand that. what I'm asking is whether the affected source images all originate from the real camera, or if the tint is experienced with generic images from other sources (piped thru the virtual device).

jsulm

@SolaVitae Looks like red part of the pixel data is missing. Can you show how you're using the camera?

SolaVitae

@Kent-Dorfman
the source image on the virtual cam is not from the real camera, its a .mp3 file, the issue also persists with just a standard .jpg file as the source as well.

@jsulm

in my application im using it as such:

WebCamDialog::WebCamDialog(QWidget *parent) :
	QDialog(parent),
	ui(new Ui::webcamdialog)
{
	ui->setupUi(this);

	includeNameCB = ui->includeNameCB;
	includeNameLE = ui->includeNameLE;
	saveImageButton = ui->savePhotoButton;
	cancelButton = ui->exitButton;

	availableCameras = ui->availableCamerasLW;
	

	if (!checkCameraAvailability()) close();

	availableCameras->setFocusPolicy(Qt::NoFocus);
	availableCameras->setPalette(p);

	cameraList = QCameraInfo::availableCameras();
	QButtonGroup bg;
	bool firstOption = true;
	foreach(const QCameraInfo &ci, cameraList) {
		QCheckBox *cam = new QCheckBox(ci.description());
		bg.addButton(cam);
		cam->setAutoExclusive(true);
		QListWidgetItem *lwi = new QListWidgetItem();
		availableCameras->addItem(lwi);
		availableCameras->setItemWidget(lwi, cam);
		availableCameraMap.insert(cam, lwi);
		connect(cam, &QCheckBox::stateChanged, this, &WebCamDialog::cameraSelectionChanged);
		if (firstOption) {
			cam->setChecked(true);
			firstOption = false;
		}
	}
	bg.setExclusive(true);	
}


void WebCamDialog::setCamera(const QCameraInfo &c) {
	m_camera.reset(new QCamera(c));
	m_camera->setViewfinder(ui->viewFinder);
	m_camera->viewfinderSettings().setResolution(1000, 1000);
	m_camera->setCaptureMode(QCamera::CaptureStillImage);

	m_camera->imageProcessing()->setWhiteBalanceMode(QCameraImageProcessing::WhiteBalanceVendor);

	qDebug() << m_camera->imageProcessing()->whiteBalanceMode();
	qDebug() << m_camera->imageProcessing()->colorFilter();


	m_imageCapture.reset(new QCameraImageCapture(m_camera.data()));
	connect(m_imageCapture.data(), &QCameraImageCapture::imageCaptured, this, &WebCamDialog::imageCaptured);
	m_camera->start();


}

void WebCamDialog::imageCaptured(int id, const QImage &i) {
	Q_UNUSED(id);
	QImage destination;
	if (!overlay.isHidden()) destination = QImage(640, 530, QImage::Format_A2RGB30_Premultiplied);
	else destination = QImage(640, 480, QImage::Format_A2RGB30_Premultiplied);

	QPainter p(&destination);

	p.setCompositionMode(QPainter::CompositionMode_Source);
	p.fillRect(destination.rect(), Qt::white);

	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	p.drawImage(0, 0, i);
	
	p.end();
	destination.save(c.directory + "\\" + ui->fileNameLE->text());

}

there is a lot of other unrelated code that I removed, but that is everything directly pertaining to the camera and viewfinder. I also have the same issue with the built in QT Camera example in QT Creator though

mranger90

@SolaVitae said in QCamera has strange blue tint:

QImage(640, 480, QImage::Format_A2RGB30_Premultiplied);

Blue tint could be because the red and blue channels are swapped. If you are in windows this is a common problem. Try using Format_A2BGR30_Premultiplied, when creating the QImage.

Kent-Dorfman

what mranger said...the color format that Qt expects to see is not what is being sent.

SolaVitae

@mranger90
it's still blue, its also blue in the viewfinder before the image is even saved

side note: The camera works perfectly, and is not blue in the QML Example from QT Creator, but is blue in the regular QT Example

Kent-Dorfman

Try different values for QCameraImageProcessing::WhiteBalanceMode and see if they have any effect.

In particular look at the definition for the white balance value you are currently using. It says "base value", which would probably infer that there is a list of vender values starting at 1000, where the required value is specific to the product being used.

SolaVitae

@Kent-Dorfman
ive tried all of them, with no change

I've narrowed the issue down to it inverting the red/blue colors

as seen in this image
alt text

The colors actually are Red - > Green - > Blue, but it inverts red and blue

mranger90

Ok, that's pretty much what I expected. The output from the camera is probably RGB but a lot of windows drivers are expecting BGR. Or it's possible (but less likely) that your camera is putting out BGR and the driver expects RGB. You might be able to change this by examining the QImageEncoderSettings to see if there is a pixel format and changing it. Or you can try intercepting the buffers and building a QImage based on the correct orientation.

SolaVitae

@mranger90

Is there an easy way to do this? seems odd that it only occurs in QT, with both my actual webcam and a virtual one, but doesn't occur in an example using QML

mranger90

You can check to see what the camera is supporting with

    QList<QVideoFrame::PixelFormat> formats = m_camera->supportedViewfinderPixelFormats();
    qDebug() << "supported formats " << formats;

Then you might be able to do something like:

viewFinderSettings.setPixelFormat(QVideoFrame::Format_RGB24);

You might also want to check with some other application. As I recall, on windows the QCamera stuff is a rather thin layer over DirectShow so you might want to play with that to get a clear idea of whats coming off the camera.
If worse comes to worst you may want to use something like OpenCV which will give you more control over the capture buffers and how to format them.

SolaVitae

@mranger90

The list returns (Format_RGB24, Format_YUV420P), its default set to the RGB24, and changing it to YUV420p does nothing.

As for testing it elsewhere, it works flawlessly everywhere else. The default camera app on windows works, a webcam testing website works, skype works.

fcarney

@SolaVitae,
Just a shot in the dark. Have you tried explicitly setting the pixel format to QVideoFrame::Format_RGB24? Just in case some other app changed its mode?

SolaVitae

@fcarney
yes, it does not change anything

The issue does not occur on my laptop, or a friend's PC. So im guessing it has something to do with my pc. What it is I can't figure out, but I guess it's not that big of a deal if it's only on my PC. It will subconciously bother me to no ender, but oh well

SGaist

Hi,

Since you are talking about a virtual camera, it might be generating BGR images. And since it's virtual you might be able to configure that.

In any case, you can use QImage::rgbSwapped to convert to the right order.