功能： 通過C程式實現圖片處理，把24bit_BMP轉為16bit_BMP

主要流程：

1）開啟圖片檔案，獲得檔案流指標

2）讀取開頭54byte，獲取圖片頭部結構體，分析圖片資訊

3）再獲取圖片的資料部分（頭部結構體之後的部分）

4）通過位偏移，把每3byte的(888RGB)轉為2byte(1555GRB)

5）把所有資料寫到另一個空的BMP檔案

#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;
}