ppm图像格式与bmp之间的相互转换

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1、ps软件可以直接导出该格式，方便快捷且免费；

2、参考https://blog.csdn.net/lingdexixixi/article/details/52354772，但是原文有一处错误，这是修改后的版本

/*真彩色bmp格式与PPM-P6之间的转换*/
#include<math.h>
#include <iomanip> 
#include <stdlib.h>
#include <windows.h>
#include <stdio.h>
 
typedef struct BGR
{
  unsigned char b;
  unsigned char g;
  unsigned char r;
}BGR;
 
typedef struct RGB
{
  unsigned char r;
  unsigned char g;
  unsigned char b;
}RGB;
 
//bpp : BMP图像的色深，即一个像素用多少位表示，常见有1、4、8、16、24和32，分别对应单色、16色、256色、16位高彩色、24位真彩色和32位增强型真彩色
void PPMtoBMP(char *pFramePPM, int bpp)
{
  FILE* pPPM;
  fopen_s(&pPPM, pFramePPM, "rb");
 
  int width, height;
  char header[20];
  fgets(header, 20, pPPM);// get "P6" 
  fgets(header, 20, pPPM);// get "width height" 
  sscanf_s(header, "%d %d\n", &width, &height);
  fgets(header, 20, pPPM);// get "255" 
 
  FILE *fp;
  fopen_s(&fp, "test.bmp", "wb");
  if (fp == NULL)
  {
    printf("file is null.\n");
    return;
  }
 
  BITMAPFILEHEADER bmpheader;
  BITMAPINFOHEADER bmpinfo;
  RGB *ppmBitsRGB = (RGB *)malloc(width*height * sizeof(RGB));
 
  bmpheader.bfType = 0x4d42;
  bmpheader.bfReserved1 = 0;
  bmpheader.bfReserved2 = 0;
  bmpheader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) - 2;
  bmpheader.bfSize = bmpheader.bfOffBits + width * height*bpp / 8;
 
  bmpinfo.biSize = sizeof(BITMAPINFOHEADER);
  bmpinfo.biWidth = width;
  bmpinfo.biHeight = height;
  bmpinfo.biPlanes = 1;
  bmpinfo.biBitCount = bpp;
  bmpinfo.biCompression = 0;//BI_RGB;
  bmpinfo.biSizeImage = width * height*bpp / 8;
  bmpinfo.biXPelsPerMeter = 100;
  bmpinfo.biYPelsPerMeter = 100;
  bmpinfo.biClrUsed = 0;
  bmpinfo.biClrImportant = 0;
 
  fwrite(&bmpheader.bfType, sizeof(bmpheader.bfType), 1, fp);
  fwrite(&bmpheader.bfSize, sizeof(bmpheader.bfSize), 1, fp);
  fwrite(&bmpheader.bfReserved1, sizeof(bmpheader.bfReserved1), 1, fp);
  fwrite(&bmpheader.bfReserved2, sizeof(bmpheader.bfReserved2), 1, fp);
  fwrite(&bmpheader.bfOffBits, sizeof(bmpheader.bfOffBits), 1, fp);
 
  fwrite(&bmpinfo.biSize, sizeof(bmpinfo.biSize), 1, fp);
  fwrite(&bmpinfo.biWidth, sizeof(bmpinfo.biWidth), 1, fp);
  fwrite(&bmpinfo.biHeight, sizeof(bmpinfo.biHeight), 1, fp);
  fwrite(&bmpinfo.biPlanes, sizeof(bmpinfo.biPlanes), 1, fp);
  fwrite(&bmpinfo.biBitCount, sizeof(bmpinfo.biBitCount), 1, fp);
  fwrite(&bmpinfo.biCompression, sizeof(bmpinfo.biCompression), 1, fp);
  fwrite(&bmpinfo.biSizeImage, sizeof(bmpinfo.biSizeImage), 1, fp);
  fwrite(&bmpinfo.biXPelsPerMeter, sizeof(bmpinfo.biXPelsPerMeter), 1, fp);
  fwrite(&bmpinfo.biYPelsPerMeter, sizeof(bmpinfo.biYPelsPerMeter), 1, fp);
  fwrite(&bmpinfo.biClrUsed, sizeof(bmpinfo.biClrUsed), 1, fp);
  fwrite(&bmpinfo.biClrImportant, sizeof(bmpinfo.biClrImportant), 1, fp);
 
  int y, x;
  for (y = 0; y < height; y++)
  {
    fread(&ppmBitsRGB[y*width], 3 * width, 1, pPPM);
    for (x = width - 1; x >= 0; x--)
    {
      fwrite(&ppmBitsRGB[y*width + x].b, 1, 1, fp);
      fwrite(&ppmBitsRGB[y*width + x].g, 1, 1, fp);
      fwrite(&ppmBitsRGB[y*width + x].r, 1, 1, fp);
    }
  }
  fclose(fp);
  fp = NULL;
  return;
}
 
void BMPtoPPM(char *pFrameRGB)
{
  FILE* pBMP;
  fopen_s(&pBMP, pFrameRGB, "rb");
  BITMAPINFOHEADER infoHeader;
  BITMAPFILEHEADER fileHeader;
  FILE *pFile;
  fopen_s(&pFile, "test.ppm", "wb");
  if (pFile == NULL)
  {
    printf("file is null.\n");
    return;
  }
  fread(&fileHeader, sizeof(BITMAPFILEHEADER), 1, pBMP);
  fread(&infoHeader, sizeof(BITMAPINFOHEADER), 1, pBMP);
 
  if (infoHeader.biBitCount != 24) {
    printf("it is not a 24-bit rgb image.\n");
    return;
  }
  long width = infoHeader.biWidth;
  long height = infoHeader.biHeight;
 
  // Write header
  fprintf(pFile, "P6\n%d %d\n255\n", width, height);
 
  // Write pixel data
  int i, j;
  BGR *bmpBitsBGR = (BGR *)malloc(width*height * sizeof(BGR));
 
  //获取每一个像素点的BGR值
  fseek(pBMP, fileHeader.bfOffBits, 0);
  for (i = 0; i < height; i++)
  {
 
    fread(&bmpBitsBGR[i*width], 3 * width, 1, pBMP);
    for (j = width - 1; j >= 0; j--)
    {
      fwrite(&bmpBitsBGR[i*width + j].r, 1, 1, pFile);
      fwrite(&bmpBitsBGR[i*width + j].g, 1, 1, pFile);
      fwrite(&bmpBitsBGR[i*width + j].b, 1, 1, pFile);
    }
    fseek(pBMP, (4 - (width% 4)) % 4, SEEK_CUR); //4字节对齐
  }
 
 
  // Close file
  fclose(pBMP);
  fclose(pFile);
  free(bmpBitsBGR);
  bmpBitsBGR = NULL;
  return;
}