【数字图像】BMP文件格式详解

/*****************************************************
   BMP文件读写 
   hatsusakana@gmail.com 
*****************************************************/

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

typedef unsigned short WORD;
typedef unsigned int DWORD;

#pragma pack(1)
typedef struct {
    WORD  bfType;
    DWORD bfSize;
    WORD  bfReserved1;
    WORD  bfReserved2;
    DWORD bfOffBits;
} BITMAP_FILE_HEADER;

typedef struct BITMAP_INFO_HEADER { 
    DWORD biSize; 
    int   biWidth; 
    int   biHeight; 
    WORD  biPlanes; 
    WORD  biBitCount; 
    DWORD biCompression; 
    DWORD biSizeImage; 
    int   biXPelsPerMeter; 
    int   biYPelsPerMeter; 
    DWORD biClrUsed; 
    DWORD biClrImportant; 
} BITMAP_INFO_HEADER;
#pragma pack()

/**
 * 32->24
 */
static void bmp_remove_aplpha (unsigned char *data, unsigned char *buf, size_t *size, size_t w, size_t h) {
    size_t i = 0, j = 0, dst_fix = 0;

    dst_fix = 4 - ((w * 24)>>3) & 3;
    *size = ((((w * 24) + 31) >> 5) << 2) * h;

    for (j = 0; j < h; j++) {
        for (i = 0; i < w; i++) {
            memcpy(buf, data, 3);
            data += 4;
            buf += 3;
        }
        buf += dst_fix;
    }
}

/**
 * 倒转图像
 */
static void bmp_reverse (unsigned char *data, unsigned char *buf, size_t size, size_t w, size_t h) {
    unsigned char *src = NULL;
    int i = 0, j = 0, preline = 0;
    
    preline = size / h;
    for (i = 0, j = h - 1; j >= 0; i++, j--) {
        src = data + j * preline;
        memcpy(buf + i * preline, src, preline);
    }
}

/**
 * bmp_read
 * 
 * 读取一个BMP文件
 * 只支持24/32位，32位会转为24位，倒转的图像会摆正
 */
unsigned char *bmp_read (const char *path, size_t *size, size_t *w, size_t *h) {
    FILE *fp = NULL;
    BITMAP_FILE_HEADER file = {0};
    BITMAP_INFO_HEADER info = {0};
    unsigned char *data = NULL, *buf = NULL;
    
    if (!path || *path == 0 || !size || !w || !h)
        return NULL;
    
    if (!(fp = fopen(path, "rb")))
        return NULL;

    if (fread(&file, 1, sizeof(BITMAP_FILE_HEADER), fp) != sizeof(BITMAP_FILE_HEADER)) {
        fclose(fp);
        return NULL;
    }

    if (fread(&info, 1, sizeof(BITMAP_INFO_HEADER), fp) != sizeof(BITMAP_INFO_HEADER)) {
        fclose(fp);
        return NULL;
    }

    //非BM开头
    if (file.bfType != 0x4d42) {
        fclose(fp);
        return NULL;
    }

    //暂时只能支持24与32位
    if (info.biBitCount != 24 && info.biBitCount != 32) {
        fclose(fp);
        return NULL;
    }

    if (info.biSizeImage == 0) {
        info.biSizeImage = info.biWidth * abs(info.biHeight) * (info.biBitCount == 24 ? 3 : 4);
    }
    
    data = (unsigned char *)malloc(sizeof(unsigned char) * info.biSizeImage);
    buf = (unsigned char *)malloc(sizeof(unsigned char) * info.biSizeImage);
    if (!data || !buf) {
        if (data) free(data);
        if (buf) free(buf);
        fclose(fp);
        return NULL;
    }
    
    if (fread(data, 1, info.biSizeImage, fp) != info.biSizeImage) {
        free(data);
        free(buf);
        fclose(fp);
        return NULL;
    }
    
    fclose(fp);
    
    *size = info.biSizeImage;
    *w = info.biWidth;
    *h = abs(info.biHeight);
    
    //32转24
    if (info.biBitCount == 32) {
        bmp_remove_aplpha(data, buf, size, *w, *h);
        memcpy(data, buf, *size);
    }
    
    //图像倒转
    if (info.biHeight > 0) {
        bmp_reverse(data, buf, *size, *w, *h);
        memcpy(data, buf, *size);
    }

    free(buf);
    return data;
}

/**
 * bmp_write
 */
int bmp_write (unsigned char *data, size_t size, size_t w, size_t h, const char *path) {
    FILE *fp = NULL;
    BITMAP_FILE_HEADER file = {0};
    BITMAP_INFO_HEADER info = {0};
    unsigned char *src = NULL;
    int hsrc = 0, preline = 0;
    
    if (!data || size == 0 || w == 0 || h == 0 || !path || *path == 0)
        return 0;
    
    if (!(fp = fopen(path, "wb+")))
        return 0;

    file.bfType = 0x4d42;
    file.bfSize = sizeof(BITMAP_FILE_HEADER) + sizeof(BITMAP_INFO_HEADER) + size;
    file.bfReserved1 = 0;
    file.bfReserved2 = 0;
    file.bfOffBits = sizeof(BITMAP_FILE_HEADER) + sizeof(BITMAP_INFO_HEADER);
    
    info.biSize = sizeof(BITMAP_INFO_HEADER);
    info.biWidth = w;
    info.biHeight = h;
    info.biPlanes = 1;
    info.biBitCount = 24;
    info.biCompression = 0L;
    info.biSizeImage = size;
    info.biXPelsPerMeter = 0;
    info.biYPelsPerMeter = 0;
    info.biClrUsed = 0;
    info.biClrImportant = 0;
    
    fwrite(&file, 1, sizeof(BITMAP_FILE_HEADER), fp);
    fwrite(&info, 1, sizeof(BITMAP_INFO_HEADER), fp);
    
    //倒转写入图像数据
    preline = size / h;
    for (hsrc = h - 1; hsrc >= 0; hsrc--) {
        src = data + hsrc * preline;
        fwrite(src, 1, preline, fp);
    }
    
    fclose(fp);
    return 1;
}

int main (int argc, char *argv[]) {
    unsigned char *data = NULL;
    size_t size = 0, w = 0, h = 0;
    
    data = bmp_read("1.bmp", &size, &w, &h);
    bmp_write(data, size, w, h, "2.bmp");
    return 1;
}