图片处理（一）之BMP格式24bit转16bit

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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;
}

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