bmp的24bit位宽转16bit

转载来自：

https://blog.csdn.net/youyoufengxinzi/article/details/1516523

#include <stdio.h
#include <stdlib.h>
#include <string.h>

#define BMP_TYPE 0x424D
#define BI_RGB               0
#define BMP1555_BYTE       2
#define BMP24_BYTE     3
#define BMP32_BYTE 4
#define CURBMP_BYTE            BMP24_BYTE
#define BMP24_TO_16(B, G, R)   ((B << 0)|(G << 5)|(R << 10))

typedef unsigned short WORD;
typedef unsigned int  DWORD;
typedef unsigned int  LONG;

#pragma pack(1)
typedef struct tagBITMAPFILEHEADER {
    WORD    bfType;
    DWORD   bfSize;
    WORD    bfReserved1;
    WORD    bfReserved2;
    DWORD   bfOffBits;
} BITMAPFILEHEADER; //7

#pragma pack(1)
typedef struct tagBITMAPINFOHEADER {
    DWORD  biSize;
    LONG   biWidth;
    LONG   biHeight;
    WORD   biPlanes;
    WORD   biBitCount;
    DWORD  biCompression;
    DWORD  biSizeImage;
    LONG   biXPelsPerMeter;
    LONG   biYPelsPerMeter;
    DWORD  biClrUsed;
    DWORD  biClrImportant;
} BITMAPINFOHEADER; //56

int main(int argc,char** argv) {
    int nErrorCode=0;
    FILE *fin;
    FILE *fout;
    char szInFilename[256];
    char szOutFilename[256];
    printf("short:%d, int:%d, long:%d. data:%d\n", sizeof(short), sizeof(int), sizeof(long), sizeof(BITMAPINFOHEADER));
    if(argc==3) {
        strcpy(szInFilename ,argv[1]);
        strcpy(szOutFilename,argv[2]);
    } else {
        printf("invalid param.\n");
        return 0;
        strcpy(szInFilename , "333.bmp");
        strcpy(szOutFilename, "444.bmp");
    }

    printf("src:%s, dest:%s\n",szInFilename,szOutFilename);
    fin  = fopen(szInFilename , "rb");
    fout = fopen(szOutFilename, "wb");

    if(fin && fout)  {
        //get BufHeader
        BITMAPFILEHEADER BmpBufHeader;
        if(fread(&BmpBufHeader, 1, sizeof(BITMAPFILEHEADER), fin))  {
            printf("Type:  0x%x\n",BmpBufHeader.bfType);
            printf("Size:  0x%x\n",BmpBufHeader.bfSize);
            printf("Offset:%d\n"  ,BmpBufHeader.bfOffBits);
        } else {
            nErrorCode |= 0x2;
        }

        //get InfoHeader
        BITMAPINFOHEADER BmpInfoHeader;
        if(fread(&BmpInfoHeader, sizeof(BITMAPINFOHEADER), 1, fin))  {
            printf("biWidth :   %d\n",BmpInfoHeader.biWidth);
            printf("biHeight:   %d\n",BmpInfoHeader.biHeight);
            printf("biBitCount: %d\n",BmpInfoHeader.biBitCount);
        } else {
            nErrorCode |= 0x4;
        }

        //handle Header
        int BmpDataNum;
        if(BmpInfoHeader.biBitCount != BMP24_BYTE*8 && BmpBufHeader.bfType != BMP_TYPE && BmpInfoHeader.biCompression != BI_RGB) {
            nErrorCode |= 0x8;
        }
        BmpInfoHeader.biBitCount  = BMP1555_BYTE * 8;
        BmpDataNum = (BmpBufHeader.bfSize - BmpBufHeader.bfOffBits) / CURBMP_BYTE;
        BmpBufHeader.bfSize = BmpDataNum * BMP1555_BYTE * 8 + BmpBufHeader.bfOffBits;
        BmpInfoHeader.biSizeImage = (BmpInfoHeader.biSizeImage * BMP1555_BYTE) / CURBMP_BYTE;

        //get BmpData
        fseek(fin, 54, SEEK_SET);
        unsigned char  *BmpDatabuff    = (unsigned char  *)malloc(CURBMP_BYTE   * BmpDataNum);
        unsigned short *BmpDatabuffNew = (unsigned short  *)malloc(BMP1555_BYTE * BmpDataNum);
        if(!fread (BmpDatabuff, 1, CURBMP_BYTE * BmpDataNum, fin))
            nErrorCode |= 0x10;
        memset(BmpDatabuffNew, 0, BMP1555_BYTE * BmpDataNum );

        //handle BmpData(important)
        int i;
        unsigned int B,G,R;
        for(i = 0; i < BmpDataNum; i++) {
            B = (BmpDatabuff[i*CURBMP_BYTE+0] >> 3)&0x1F;//blue
            G = (BmpDatabuff[i*CURBMP_BYTE+1] >> 3)&0x1F;//green
            R = (BmpDatabuff[i*CURBMP_BYTE+2] >> 3)&0x1F;//red
            BmpDatabuffNew[i] = (unsigned short)BMP24_TO_16(B, G, R);
        }

        //creat NewBmp
        fseek(fout, 0, SEEK_SET);
        if(!fwrite(&BmpBufHeader , 1, sizeof(BITMAPFILEHEADER), fout))  {
            nErrorCode |= 0x20;
        }
        if(!fwrite(&BmpInfoHeader, 1, sizeof(BITMAPINFOHEADER), fout))  {
            nErrorCode |= 0x40;
        }
        fseek(fout, 54, SEEK_SET);
        if(!fwrite(BmpDatabuffNew, BMP1555_BYTE, BmpDataNum, fout)) {
            nErrorCode |= 0x80;
        }

    } else{
        nErrorCode |= 0x1;
    }

    if(fin) {
        fclose(fin);
    }
    if(fout) {
        fclose(fout);
    }
    printf("nErrorCode: %d\n", nErrorCode);
    printf("BMP32_TO_16:%s\n",!nErrorCode?"success":"fail");
    return nErrorCode;
}