使用GDAL实现常用图像格式(JPEG、PNG32、PNG24)之间的转换

主要思路

• 使用GDAL库实现图像类型转换功能
• 读取原始图像的数据，返回图像的宽、高、通道数量
• 创建内存驱动器，将原始图像的数据写入到内存驱动器中
• 使用CreateCopy接口，将内存驱动器的数据生成要求的jpg或者png图像
  • 读取和写入的时候，都是按通道从0 0位置开始一次性读取图像宽和高数量的像素。
  • 按照源图像的通道数量作为间隔拷贝原始数据到内存驱动器中。

参考网址

https://www.cnblogs.com/xiangism/p/5311314.html

https://blog.csdn.net/godenlove007/article/details/8864763

读取图像原始数据

	    bool ReadImageData( unsigned char **pImageData,int &nWidth,int &nHeight,int &nChannels,const QString& strFilePath )
		{
			GDALAllRegister();
			GDALDataset *poDataset = NULL;
	
			CPLSetConfigOption("GDAL_FILENAME_IS_UTF8","NO");
	
			poDataset=(GDALDataset*) GDALOpen(strFilePath.toLocal8Bit(),GA_ReadOnly);	
			if(poDataset == NULL)
			{
				//qDebug()<GetRasterXSize();
			nHeight = poDataset->GetRasterYSize();
			nChannels = poDataset->GetRasterCount();
	
			*pImageData = new unsigned char[nChannels * nWidth * nHeight];		
			ZeroMemory(*pImageData,nChannels * nWidth * nHeight);
	
			for (int i = 1; i <= nChannels; ++ i)
			{
				unsigned char *pImageOffset = *pImageData + i - 1;
				GDALRasterBand* pBand = poDataset->GetRasterBand(i);
	
				pBand->RasterIO(
					GF_Read,
					0,0,			
					nWidth,nHeight,	
					pImageOffset,	
					nWidth,nHeight,	
					GDT_Byte,		
					nChannels,				
					0);				
			}
	
			GDALClose(poDataset);
			return true;
		}

创建指定格式的图像

• GetDriverType就是根据目标文件后缀名获取对应的驱动器类型：比如".jpg"对应"JPEG"。

• 创建完成后注意数据集的释放。

    	bool WriteImageData(const QString& strDestFilePath,unsigned char* pImageData,int nWidth,int nHeight,int nChannels,int nNewChannels)
    	{
    		CPLSetConfigOption("GDAL_FILENAME_IS_UTF8","NO");
    
    		GDALAllRegister();
    
    		QString strType;
    		GetDriverType(strDestFilePath,strType);
    
    		GDALDriver *pMemDriver = NULL;
    		pMemDriver = GetGDALDriverManager()->GetDriverByName("MEM");
    		if( pMemDriver == NULL ) { return false; }
    
    		GDALDataset * pMemDataSet = pMemDriver->Create("",nWidth,nHeight,nNewChannels,GDT_Byte,NULL);
    		GDALRasterBand *pBand = NULL;
    
    		for (int i = 1; i <= nNewChannels; i++)
    		{
    			if (i==nNewChannels && nNewChannels >nChannels)
    			{
    				unsigned char *pTempImageData = new unsigned char[nNewChannels*nWidth*nHeight];
    				memset(pTempImageData,0xFE,nNewChannels*nWidth*nHeight);
    
    				pBand = pMemDataSet->GetRasterBand(i);
    				pBand->RasterIO(GF_Write, 
    					0, 
    					0, 
    					nWidth, 
    					nHeight, 
    					pTempImageData, 
    					nWidth, 
    					nHeight, 
    					GDT_Byte, 
    					nNewChannels, 
    					0); 
    			}
    			else
    			{
    				pBand = pMemDataSet->GetRasterBand(i);
    				pBand->RasterIO(GF_Write, 
    					0, 
    					0, 
    					nWidth, 
    					nHeight, 
    					pImageData+i-1 , 
    					nWidth, 
    					nHeight, 
    					GDT_Byte, 
    					nChannels, 
    					0); 
    			}
    		}
    
    		GDALDriver *pDstDriver = NULL;
    		pDstDriver = (GDALDriver *)GDALGetDriverByName(strType.toStdString().c_str());
    		if (pDstDriver == NULL)
    		{ 
    			GDALClose(pMemDataSet); 
    
    			return false;
    		}
    
    		GDALDataset * pDataSet = pDstDriver->CreateCopy(strDestFilePath.toLocal8Bit(),pMemDataSet,FALSE, NULL, NULL, NULL);
    		if (pDataSet == NULL)
    		{
    			GDALClose(pMemDataSet); 
    
    			return false;
    		}
    
    		GDALClose(pDataSet); 
    		GDALClose(pMemDataSet); 
    
    		return true; 
    	}