Convert Mat to QPixmap

Question

How can we convert directly cv::Mat to QPixmap without going through filename loading?

I have made some research about it but no hints!

As a first step, what I have tried is that I save the image, and then load it. But it's not what I want to have.

Grillparzer

You could probably use the function QPixmap::loadFromData(...) to load the field cv::Mat::data directly into the QPixmap. I never tried to do such a thing though. – Eastsoutheast

And by the way, possible duplicate since it's easy to switch between Qimage and QPixmap. – Eastsoutheast

And how to switch between QImage and QPixmap? – Grillparzer

Cannot be easier: QPixmap::fromImage(). – Eastsoutheast

Answer 1

Jehan is right.

For people referring to this thread in the future: First convert image from BGR(used by OpenCV) to RGB.

Then:

QPixmap::fromImage(QImage((unsigned char*) mat.data, mat.cols, mat.rows, QImage::Format_RGB888));

Tall

You can also use QPixmap::fromImage(QImage((unsigned char*) mat.data, mat.cols, mat.rows, QImage::Format_RGB888).rgbswapped()); so you dont have to convert image before starting – Whitcomb

This isn't working for Mat3b. What exactly could be the reason? – Boorman

QPixmap pix= QPixmap::fromImage(QImage((unsigned char*) img.data, img.cols, img.rows, QImage::Format_RGB888).rgbSwapped()); ui->mylable->setPixmap(pix); – Yammer

After Qt 5.14 there is a new QImage format QImage::Format_BGR888 so a better method is to specify the format as QImage::Format_BGR888 and no need to convert colors now. – Tony

Answer 2

Mehfoos Yacoob is right, that is the best way to convert a cv::Mat to a QPixmap. First, you need to convert the cv::Mat to a QImage, and then using the fromImage function, assign its result to a QPixmap. It is important to keep in mind the type of the cv::Mat in order to use the correct QImage format.

This is a little example of how to do it: http://asmaloney.com/2013/11/code/converting-between-cvmat-and-qimage-or-qpixmap/

Pallor

as additional information to this solution (as told in https://mcmap.net/q/337426/-how-to-convert-an-opencv-cv-mat-to-qimage) is that "some images won't show properly without it." -> add the mat.step as 4th parameter. The example linked above to asmaloney also includes that parameter it his calls. – Sip