读/写PPM图像文件C++

Question

尝试以我知道的方式读取和写入PPM图像文件(.ppm):

std::istream& operator >>(std::istream &inputStream, PPMObject &other)
{
    inputStream.seekg(0, ios::end);
    int size = inputStream.tellg();
    inputStream.seekg(0, ios::beg);

    other.m_Ptr = new char[size];


    while (inputStream >> other.m_Ptr >> other.width >> other.height >> other.maxColVal)
    {
        other.magicNum = (string) other.m_Ptr;
    }

    return inputStream;
}

我的值对应于实际文件.所以我乐意尝试写数据:

std::ostream& operator <<(std::ostream &outputStream, const PPMObject &other)
{
    outputStream << "P6"     << " "
        << other.width       << " "
        << other.height      << " "
        << other.maxColVal   << " "
       ;

    outputStream << other.m_Ptr;

    return outputStream;
}

我确保使用std :: ios :: binary打开文件进行读写:

int main ()
{
    PPMObject ppmObject = PPMObject();
    std::ifstream image;
    std::ofstream outFile;

    image.open("C:\\Desktop\\PPMImage.ppm", std::ios::binary);
    image >> ppmObject;

    image.clear();
    image.close();

    outFile.open("C:\\Desktop\\NewImage.ppm", std::ios::binary);
    outFile << ppmObject;

    outFile.clear();
    outFile.close();

    return 0;
}

逻辑错误:

我只写了一部分图像.标题没有问题或手动打开文件.

类公共成员变量:

m_Ptr成员变量是char*,height,width maxColrVal都是整数.

尝试解决方案:

使用inputStream.read和outputStream.write来读取和写入数据,但我不知道我尝试过的方式和方法不起作用.

由于我的char*m_Ptr包含所有像素数据.我可以遍历它:

for (int I = 0; I < other.width * other.height; I++) outputStream << other.m_Ptr[I];

但由于某种原因,这会导致运行时错误.

Answer 1

基于http://fr.wikipedia.org/wiki/Portable_pixmap,P6是二进制图像.这会读取单个图像.请注意,不执行检查.这需要添加.

std::istream& operator >>(std::istream &inputStream, PPMObject &other)
{
    inputStream >> other.magicNum;
    inputStream >> other.width >> other.height >> other.maxColVal;
    inputStream.get(); // skip the trailing white space
    size_t size = other.width * other.height * 3;
    other.m_Ptr = new char[size];
    inputStream.read(other.m_Ptr, size);
    return inputStream;
}

此代码写入单个图像.

std::ostream& operator <<(std::ostream &outputStream, const PPMObject &other)
{
    outputStream << "P6"     << "\n"
        << other.width       << " "
        << other.height      << "\n"
        << other.maxColVal   << "\n"
       ;
    size_t size = other.width * other.height * 3;
    outputStream.write(other.m_Ptr, size);
    return outputStream;
}

m_Ptr仅包含RGB像素值.

我在网上下载的图像(http://igm.univ-mlv.fr/~incerti/IMAGES/COLOR/Aerial.512.ppm)上测试了代码,并使用了以下结构PPMObject.

struct PPMObject
{
  std::string magicNum;
  int width, height, maxColVal;
  char * m_Ptr;
};