用 C++ 编写 PPM 文件并得到扭曲的结果

Question

我必须读取、修改和写入 PPM 图像。我试图通过尝试将 PPM 图像写入新文件来检查我是否在我的数组中正确获取了 PPM 图像的所有数据。但是我得到的图像看起来像一台坏掉的电视：a pattern of this:

我不知道我做错了什么，我至少想知道一种方法来检查可能出错的地方。这些是我的代码： 主要的： 图片实例；

string filename = "Image03.ppm";
string format = "ppm";
bool fileWritten = false;
if (instance.load(filename, format)) {
    cout << "The file has been successfully loaded" << endl;

    cout << "The dimensions of the image are:" << endl;
    cout << instance.getWidth() << "x" << instance.getHeight() << endl;

...

bool imaging::Image::load(const string & filename, const string & format){
        string extension = filename.substr(filename.find_last_of(".") + 1);
        bool flag = false; // to stop the loop when a different letter is found.
        bool result = false; // stores the return value
        unsigned int sz = extension.size();
        for (unsigned int i = 0; i < sz; ++i) {
            if (tolower(extension[i]) != tolower(format[i]) && !flag) {
                cout << "The extension of the file does not match the required format." << endl;

                flag = true;

            }
        }

        if (!flag) {
            string filename1 = filename;
            const char *cstr = filename1.c_str();
            int pw = 0;
            int ph = 0;
            float* buff = ReadPPM(cstr, &pw, &ph);
            width = pw;
            height = ph;
            bool h = WritePPM(buff, width, height, "kokoo.ppm");

...

bool WritePPM(const float * data, int w, int h, const char * filename) {
        ofstream myfile;
        myfile.open(filename, ios::out | ios::binary);

        myfile << "P6\n" << w << "\n" << h << "\n255\n";
        for (int i = 0; i < w*h; i++) {
            myfile.write((char*)&data[i], sizeof(float));
        }
        myfile.close();
        return 0;
    }

...

float * ReadPPM(const char * filename, int* w, int* h) {
        ifstream myfile;
        myfile.open(filename,  ios::binary);
        if (myfile.is_open())
        {
            int i = 0;
            string letter;
            cout << "File successfully open" << endl;

            myfile.ignore(2, ' ');
            int width;
            int height;
            myfile >> width;
            myfile >> height;
            myfile.ignore(4, ' ');

            *w = width;
            *h =  height;

            int size = width*height * 3;
            int k = myfile.peek();
            while (k == 32) {                           //32 is ascii for whitespace.
                myfile.ignore(256,' ');
                k = myfile.peek();
            }
            unsigned char * temp = new unsigned char[size];
            myfile.read((char*)temp, size);
            float * buff = new float[size];



            while (i < size) {  
                buff[i] = (float)temp[i]/255;
                i++;
                cout << "before" << buff[i] << endl;
                cin.get();
            }

            delete[] temp;
            return buff;
            myfile.close();
        }
        else
        {
            cout << "Error opening file";
            cin.get();
            return 0;
        }




    }

即使我的代码看起来很傻，这也是我对这门语言不熟悉的原因，除非我做错了什么，否则我喜欢它的外观，反正这是一个作业。

Answer 1

如果你真的必须转换为浮点数组，这就是你做错的地方：

WritePPM 中的循环完全错误。您忘记了 3，忘记了乘以 255 来缩减，并且无法将浮点值写入 PPM。它应该是这样的：

for (int i = 0; i < 3*w*h; i++) {
    unsigned char c = (unsigned char) (255.0f * data[i] + 0.5f); 
    myfile.write((char*) &c, sizeof(c));
}

我没有检查所有其他代码，但是您肯定还有一些其他错误，例如在ReadPPM中的return语句之后关闭文件。