C++ Mat与AVFrame，QImage的转换

前言

ffmpeg，opencv，qt 在视频应用开发的时候会经常用到，因此总结性转换的方法

• AVFrame转cv::Mat

void avframeToMat(const AVFrame * frame, cv::Mat& image)
{
	int w = frame->width;
	int h = frame->height;
	struct SwsContext *sws_ctx = NULL;
	sws_ctx = sws_getContext(frame->width, frame->height, (enum AVPixelFormat)frame->format,
		w, h, AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);

	//cv::Mat mat;
	image.create(cv::Size(w, h), CV_8UC3);
	AVFrame *bgr24frame = av_frame_alloc();
	bgr24frame->data[0] = (uint8_t *)image.data;
	avpicture_fill((AVPicture *)bgr24frame, bgr24frame->data[0], AV_PIX_FMT_BGR24, w, h);
	sws_scale(sws_ctx,
		(const uint8_t* const*)frame->data, frame->linesize,
		0, frame->height, // from cols=0,all rows trans
		bgr24frame->data, bgr24frame->linesize);

	av_free(bgr24frame);
	sws_freeContext(sws_ctx);
	return;
}

• QImage 转 cv::Mat

cv::Mat QImage2cvMat(QImage image)
{
	cv::Mat mat;
	switch (image.format())
	{
	case QImage::Format_ARGB32:
	case QImage::Format_RGB32:
	case QImage::Format_ARGB32_Premultiplied:
		mat = cv::Mat(image.height(), image.width(), CV_8UC4, (void*)image.constBits(), image.bytesPerLine());
		break;
	case QImage::Format_RGB888:
		mat = cv::Mat(image.height(), image.width(), CV_8UC3, (void*)image.constBits(), image.bytesPerLine());
		cv::cvtColor(mat, mat, CV_BGR2RGB);
		break;
	case QImage::Format_Indexed8:
		mat = cv::Mat(image.height(), image.width(), CV_8UC1, (void*)image.constBits(), image.bytesPerLine());
		break;
	}
	return mat;
}

• cv::Mat 转QImage

QImage cvMat2QImage(const cv::Mat& mat)
{
  
	if (mat.type() == CV_8UC1)
	{
		QImage image(mat.cols, mat.rows, QImage::Format_Indexed8);
		// Set the color table (used to translate colour indexes to qRgb values)  
		image.setColorCount(256);
		for (int i = 0; i < 256; i++)
		{
			image.setColor(i, qRgb(i, i, i));
		}
		// Copy input Mat  
		uchar *pSrc = mat.data;
		for (int row = 0; row < mat.rows; row++)
		{
			uchar *pDest = image.scanLine(row);
			memcpy(pDest, pSrc, mat.cols);
			pSrc += mat.step;
		}
		return image;
	}
	// 8-bits unsigned, NO. OF CHANNELS = 3  
	else if (mat.type() == CV_8UC3)
	{
		// Copy input Mat  
		const uchar *pSrc = (const uchar*)mat.data;
		// Create QImage with same dimensions as input Mat  
		QImage image(pSrc, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);
		return image.rgbSwapped();
	}
	else if (mat.type() == CV_8UC4)//opencv 会从这里转
	{
		//qDebug() << "CV_8UC4";
		// Copy input Mat  
		const uchar *pSrc = (const uchar*)mat.data;
		// Create QImage with same dimensions as input Mat  
		QImage image(pSrc, mat.cols, mat.rows, mat.step, QImage::Format_RGB32);
		return image.copy();
	}
	else
	{
		//qDebug() << "ERROR: Mat could not be converted to QImage.";
		return QImage();
	}
}