C++ 将PPM图像转换为灰度C++；

尝试通过索引包含像素数据的指针，将PPM图像转换为灰度：

void PPMObject::greyScale()
{
    const float r = 0.299F;
    const float g = 0.587F;
    const float b = 0.114F;

    int size = this->width * this->height * 3;
    for (int i = 0; i < size; i++)
    {
        this->m_Ptr[i] = (this->m_Ptr[i] * r) + (this->m_Ptr[i] * g) + (this->m_Ptr[i] * b);
        this->m_Ptr[i+1] = (this->m_Ptr[i+1] * r) + (this->m_Ptr[i+1] * g) + (this->m_Ptr[i+1] * b);
        this->m_Ptr[i+2] = (this->m_Ptr[i+2] * r) + (this->m_Ptr[i+2] * g) + (this->m_Ptr[i+2] * b);
    }
}

我把数据写如下：

ostream& operator <<(ostream &outputStream, const PPMObject &other)
{
    outputStream << other.magicNum  << " "
    << other.width          << " "
    << other.height         << " "
    << other.maxColorValue  << " "
    ;   
    outputStream.write(other.m_Ptr, other.width * other.height * 3);
    return outputStream;
}

ostream&operator在greyScale（）函数中，每次遍历循环时都需要将i增加3，因为每个像素占用3个字节，每次处理一个像素：

for (int i = 0; i < size; i+=3)

简化为：

 this->m_Ptr[i] = (this->m_Ptr[i] * 1.0F);

正确的公式如下所示（忽略强制转换并假设数据按RGB顺序排列）：

for（int i=0；im_Ptr[i]*r）+（this->m_Ptr[i+1]*g）+（this->m_Ptr[i+2]*b）；
此->m_Ptr[i]=灰度标度值；
此->m_Ptr[i+1]=灰度标度值；
此->m_Ptr[i+2]=灰度标度值；
}
我今天早些时候编写的以下程序成功地将彩色图像（.ppm）文件转换为灰度图像（.ppm）文件。我添加了很多评论，所以你可以很容易地跟随

#include <fstream>
#include <iostream>
#include <string>

using namespace std;

int main() {
    //File input and output streams
    ifstream fin("colorImage.ppm");
    ofstream fout("grayscaleImage.ppm");
    //Check if input file was successfully opened
    if (!fin) {
        cout << "Error - Nonexistent Image (.ppm) File" << endl;
        system("pause");
        return -1;  // Error exit
    }
    //Declare necessary variables
    string magic_number;
    int pixel_per_row, num_rows, color_depth, red, green, blue;
    //Read in values for the following variables from input file
    fin >> magic_number >> pixel_per_row >> num_rows >> color_depth;
    //Write the following variables to the output file
    fout << magic_number << endl << pixel_per_row << " " << num_rows << endl << color_depth << endl;
    //Read in input file until file end putting values into appropriate variables
    while (fin >> red >> green >> blue) {
        red = green = blue = int(0.3 * red + 0.59 * green + 0.11 * blue); //Covert each pixel to grayscale
        fout << red << endl << green << endl << blue << endl; //Write converted values to output file
    }
    //Close files
    fin.close();
    fout.close();
    return 0;
}

#包括
#包括
#包括
使用名称空间std；
int main（）{
//文件输入和输出流
ifstream fin（“colorImage.ppm”）；
流fout（“grayscaleImage.ppm”）；
//检查输入文件是否已成功打开
如果（！fin）{
cout magic_number>>每行像素数>>行数>>颜色深度；
//将以下变量写入输出文件
谢谢！如果我有更多的经验，我应该自己抓住这些错误。
 this->m_Ptr[i] = (this->m_Ptr[i] * 1.0F);

for (int i = 0; i < size; i+=3)
{
    float greyscaleValue = (this->m_Ptr[i] * r) + (this->m_Ptr[i+1] * g) + (this->m_Ptr[i+2] * b);
    this->m_Ptr[i] = greyscaleValue;
    this->m_Ptr[i+1] = greyscaleValue;
    this->m_Ptr[i+2] = greyscaleValue;
}

#include <fstream>
#include <iostream>
#include <string>

using namespace std;

int main() {
    //File input and output streams
    ifstream fin("colorImage.ppm");
    ofstream fout("grayscaleImage.ppm");
    //Check if input file was successfully opened
    if (!fin) {
        cout << "Error - Nonexistent Image (.ppm) File" << endl;
        system("pause");
        return -1;  // Error exit
    }
    //Declare necessary variables
    string magic_number;
    int pixel_per_row, num_rows, color_depth, red, green, blue;
    //Read in values for the following variables from input file
    fin >> magic_number >> pixel_per_row >> num_rows >> color_depth;
    //Write the following variables to the output file
    fout << magic_number << endl << pixel_per_row << " " << num_rows << endl << color_depth << endl;
    //Read in input file until file end putting values into appropriate variables
    while (fin >> red >> green >> blue) {
        red = green = blue = int(0.3 * red + 0.59 * green + 0.11 * blue); //Covert each pixel to grayscale
        fout << red << endl << green << endl << blue << endl; //Write converted values to output file
    }
    //Close files
    fin.close();
    fout.close();
    return 0;
}