图片处理（一）之BMP格式24bit转16bit

功能： 通过C程序实现图片处理，把24bit_BMP转为16bit_BMP

主要流程：

1）打开图片文件，获得文件流指针

2）读取开头54byte，获取图片头部结构体，分析图片信息

3）再获取图片的数据部分（头部结构体之后的部分）

4）通过位偏移，把每3byte的(888RGB)转为2byte(1555GRB)

5）把所有数据写到另一个空的BMP文件

#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 long  LONG;

#pragma pack(1)

typedef struct tagBITMAPFILEHEADER 

{     
WORD    bfType;     
DWORD   bfSize;     
WORD    bfReserved1;     
WORD    bfReserved2;     
DWORD   bfOffBits; 

} BITMAPFILEHEADER;

#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; 

int main(int argc,char** argv)

{
int nErrorCode=0;
FILE *fin;
FILE *fout;
char szInFilename[256];
char szOutFilename[256];
if(argc==3)
{
strcpy(szInFilename ,argv[1]);
strcpy(szOutFilename,argv[2]);
}
else
{
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    = malloc(CURBMP_BYTE   * BmpDataNum);

    unsigned short *BmpDatabuffNew = 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");
system("pause");
return nErrorCode;

}