我正在编写一个简单的程序来将灰度二进制 (P5) 转换为灰度 ascii (P2)，但是在读取二进制并将其转换为 int 时遇到问题。
#include <iostream>
#include <fstream>
#include <sstream>
using namespace::std;
int usage(char* arg) {
// exit program
cout << arg << ": Error" << endl;
return -1;
}
int main(int argc, char* argv[]) {
int rows, cols, size, greylevels;
string filetype;
// open stream in binary mode
ifstream istr(argv[1], ios::in | ios::binary);
if(istr.fail()) return usage(argv[1]);
// parse header
istr >> filetype >> rows >> cols >> greylevels;
size = rows * cols;
// check data
cout << "filetype: " << filetype << endl;
cout << "rows: " << rows << endl;
cout << "cols: " << cols << endl;
cout << "greylevels: " << greylevels << endl;
cout << "size: " << size << endl;
// parse data values
int* data = new int[size];
int fail_tracker = 0; // find which pixel failing on
for(int* ptr = data; ptr < data+size; ptr++) {
char t_ch;
// read in binary char
istr.read(&t_ch, sizeof(char));
// convert to integer
int t_data = static_cast<int>(t_ch);
// check if legal pixel
if(t_data < 0 || t_data > greylevels) {
cout << "Failed on pixel: " << fail_tracker << endl;
cout << "Pixel value: " << t_data << endl;
return usage(argv[1]);
}
// if passes add value to data array
*ptr = t_data;
fail_tracker++;
}
// close the stream
istr.close();
// write a new P2 binary ascii image
ofstream ostr("greyscale_ascii_version.pgm");
// write header
ostr << "P2 " << rows << cols << greylevels << endl;
// write data
int line_ctr = 0;
for(int* ptr = data; ptr < data+size; ptr++) {
// print pixel value
ostr << *ptr << " ";
// endl every ~20 pixels for some readability
if(++line_ctr % 20 == 0) ostr << endl;
}
ostr.close();
// clean up
delete [] data;
return 0;
}
示例图片- 从旧帖子中提取。删除了图像文件中的注释，因为我现在不担心这个功能。
当用 g++ 编译时，我得到输出：
$> ./a.out a.pgm
filetype: P5
rows: 1024
cols: 768
greylevels: 255
size: 786432
Failed on pixel: 1
Pixel value: -110
a.pgm: Error
图像是一只小鸭子，像素值不可能是-110 ......我哪里出错了？谢谢。