ppm图像格式与bmp之间的相互转换

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
#include  
#include 
#include 
#include 

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;
}