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.geek-share.com/detail/2670388402.html

https://www.geek-share.com/detail/2578149743.html

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()<<QString::fromLocal8Bit("%1 GDAL打开失败").arg(strFilePath);
GDALClose(poDataset);
return false;
}

nWidth = poDataset->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;
  }