读取多波段的tif(利用GDAL)

bmp的格式是RGBRGB.....排列下来的，每个像素的三个分量靠在一起，描述完一个像素，接着描述下一个像素。

tif的格式更多样。通常的格式也是BGRBGR.....(次序与bmp相反)排列下来的，但偶尔有一些tif文件采用RRRRRR.......GGGGG.........BBBBB.....的安排。还有的tif文件内容是压缩过的。。。。这里我们只考虑三个颜色分量靠在一起的情况。

下面的例子是一个tif文件，宽896,高608,三个分量。这里直接用gdal读取tif，再写入bmp。与前面《一个tif转bmp的示例》不同，使用gdal不需要手动交换B-R的位置。
具体项目见我的资源中的"gdalTif.rar"

#include <gdal_priv.h>
#include <algorithm>
#include <iostream>
#include <fstream>

#pragma comment(lib, "gdal_i.lib")

bool bReadImageMultiBand(unsigned char * & pImgData, int & iWidth, int & iHeight, int & iChannel, char * strPath);
bool bWriteImageData(char *, unsigned char *, int, int, int, int);
void vFindImageTypeGDAL(char *, char *);

int main(void)
{
	GDALAllRegister();
	int iWidth, iHeight, iChannel;
	unsigned char * pImgData;
	if(bReadImageMultiBand(pImgData, iWidth, iHeight, iChannel, "earthRGBRGB.tif"))
	{
		bWriteImageData("earth.bmp", pImgData, iWidth, iHeight, iChannel, iChannel);
		delete [] pImgData;
	}

	return 0;
}

bool bReadImageMultiBand(unsigned char * & pImgData, int & iWidth, int & iHeight, int & iChannel, char * strPath)
{
	GDALDataset * pDataSet = nullptr;
	pDataSet = (GDALDataset *)GDALOpen(strPath, GA_ReadOnly);
	if(pDataSet == nullptr)
	{
		GDALClose(pDataSet);
		return false;
	}

	GDALDataType dt = pDataSet->GetRasterBand(1)->GetRasterDataType();
	iWidth = pDataSet->GetRasterXSize();
	iHeight = pDataSet->GetRasterYSize();
	iChannel = std::min(pDataSet->GetRasterCount(), 3);
	int arrBandMap[] = {1,2,3};
	pImgData = new unsigned char[iWidth * iHeight * iChannel];
	pDataSet->RasterIO(GF_Read, 0,0, iWidth, iHeight, pImgData, iWidth, iHeight, dt, iChannel, arrBandMap, 0,0,0);
	GDALClose(pDataSet);

	return true;
}

bool bWriteImageData(char * strDestPath, unsigned char * pData, int iWidth, int iHeight, int iSrcChannel, int iDestChannel)
{
	char arrType[1024] = {0};
	vFindImageTypeGDAL(strDestPath, arrType);

	if(arrType)
	{
		std::fstream file;
		file.open(strDestPath, std::ios_base::out);
		file.close();
		GDALDriver * pMemDriver = GetGDALDriverManager()->GetDriverByName("MEM");
		if(pMemDriver == nullptr)
			return false;

		GDALDataset * pMemDataSet = pMemDriver->Create("",iWidth,iHeight,iDestChannel,GDT_Byte,NULL);
        GDALRasterBand *pBand = NULL;
		int arrBandMap[3] = { 1, 2, 3 };
		pMemDataSet->RasterIO(GF_Write,
			0,
			0,
			iWidth,
			iHeight,
			pData,
			iWidth,
			iHeight,
			GDT_Byte,
			iDestChannel,
			arrBandMap,
			0,0,0);

        GDALDriver *pDstDriver = NULL;
        pDstDriver = (GDALDriver *)GDALGetDriverByName(arrType);
        if (pDstDriver == NULL)
        {
            GDALClose(pMemDataSet);

            return false;
        }

        GDALDataset * pDataSet = pDstDriver->CreateCopy(strDestPath,pMemDataSet,FALSE, NULL, NULL, NULL);
        if (pDataSet == NULL)
        {
            GDALClose(pMemDataSet);

            return false;
        }

        GDALClose(pDataSet);
        GDALClose(pMemDataSet);

        return true;
    }
    else
    {
        return false;
    }
}

void vFindImageTypeGDAL(char * pDstImgFileName, char * pDst)
{
	char * dstExtension = strlwr(strrchr(pDstImgFileName, '.') + 1);

	if (0 == strcmp(dstExtension, "bmp"))
		sprintf(pDst, "%s", "BMP");
	else if (0 == strcmp(dstExtension, "jpg"))
		sprintf(pDst, "%s", "JPEG");
	else if (0 == strcmp(dstExtension, "png"))
		sprintf(pDst, "%s", "PNG");
	else if (0 == strcmp(dstExtension, "tif"))
		sprintf(pDst, "%s", "GTiff");
	else if (0 == strcmp(dstExtension, "gif"))
		sprintf(pDst, "%s", "GIF");
}