代码如下：

#include
#include
#include


#pragma pack(1)
typedef struct tagBITMAPFILEHEADER
{
    unsigned char bfType[2];//文件格式
    unsigned long bfSize;//文件大小
    unsigned short bfReserved1;//保留
    unsigned short bfReserved2;
    unsigned long bfOffBits; //DIB数据在文件中的偏移量
}fileHeader;
#pragma pack()
/*
位图数据信息结构
*/
#pragma pack(1)
typedef struct tagBITMAPINFOHEADER
{
    unsigned long biSize;//该结构的大小
    long biWidth;//文件宽度
    long biHeight;//文件高度
    unsigned short biPlanes;//平面数
    unsigned short biBitCount;//颜色位数
    unsigned long biCompression;//压缩类型
    unsigned long biSizeImage;//DIB数据区大小
    long biXPixPerMeter;
    long biYPixPerMeter;
    unsigned long biClrUsed;//多少颜色索引表
    unsigned long biClrImporant;//多少重要颜色
}fileInfo;
#pragma pack()
/*
调色板结构
*/
#pragma pack(1)
typedef struct tagRGBQUAD
{
    unsigned char rgbBlue; //蓝色分量亮度
    unsigned char rgbGreen;//绿色分量亮度
    unsigned char rgbRed;//红色分量亮度
    unsigned char rgbReserved;
}rgbq;
#pragma pack()

int main()
{
    FILE *fp1 = fopen("C:\\Users\\Administrator\\Desktop\\data\\bmp\\image.bmp", "rb+");
    if (fp1 == NULL)
    {
        printf("打开文件fp1失败");
        exit(0);
    }

    FILE *fp2 = fopen("C:\\Users\\Administrator\\Desktop\\data\\bmp\\imageGray.bmp", "wb");
    if (fp1 == NULL)
    {
        printf("打开文件fp2失败");
        exit(0);
    }

    fileHeader * fh;
    fileInfo * fi;
    fh = (fileHeader *)malloc(sizeof(fileHeader));
    fi = (fileInfo *)malloc(sizeof(fileInfo));

    //读取位图头结构和信息头
    fread(fh, sizeof(fileHeader), 1, fp1);
    fread(fi, sizeof(fileInfo), 1, fp1);

    printf("\\\\\\\\\\\\\\\\\\\\原始图片信息\\\\\\\\\\\\\\\\\\\\\\\\\\\n");
    printf("bmp文件头：\n");
    printf("bfSize:%d\n", fh->bfSize);
    printf("bfOffBits:%d\n", fh->bfOffBits);
    printf("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n");
    printf("bmp信息头\n");
    printf("结构体长度：%d \n", fi->biSize);
    printf("位图宽度：%d \n", fi->biWidth);
    printf("位图高度：%d \n", fi->biHeight);
    printf("位图平面数：%d \n", fi->biPlanes);
    printf("颜色位数：%d \n", fi->biBitCount);
    printf("压缩方式：%d \n", fi->biCompression);
    printf("实际位图数据占用的字节数：%d \n", fi->biSizeImage);
    printf("X方向分辨率：%d \n", fi->biXPixPerMeter);
    printf("Y方向分辨率：%d \n", fi->biYPixPerMeter);
    printf("使用的颜色数：%d \n", fi->biClrUsed);
    printf("重要颜色数：%d \n", fi->biClrImporant);
    printf("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n");

    //修改信息头
    fi->biBitCount = 8;
    //fi->biSizeImage = ((fi->biWidth * 3 + 3) / 4) * 4 * fi->biHeight;
    fi->biSizeImage = fi->biHeight*fi->biWidth;
    //修改文件头
    fh->bfOffBits = sizeof(fileHeader) + sizeof(fileInfo) + 256 * sizeof(rgbq);
    fh->bfSize = fh->bfOffBits + fi->biSizeImage;

    printf("\\\\\\\\\\\\\\\\\\\\修改后的图片信息\\\\\\\\\\\\\\\\\\\\\\\\\\\n");
    printf("bmp文件头：\n");
    printf("bfSize:%d\n", fh->bfSize);
    printf("bfOffBits:%d\n", fh->bfOffBits);
    printf("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n");
    printf("bmp信息头\n");
    printf("结构体长度：%d \n", fi->biSize);
    printf("位图宽度：%d \n", fi->biWidth);
    printf("位图高度：%d \n", fi->biHeight);
    printf("位图平面数：%d \n", fi->biPlanes);
    printf("颜色位数：%d \n", fi->biBitCount);
    printf("压缩方式：%d \n", fi->biCompression);
    printf("实际位图数据占用的字节数：%d \n", fi->biSizeImage);
    printf("X方向分辨率：%d \n", fi->biXPixPerMeter);
    printf("Y方向分辨率：%d \n", fi->biYPixPerMeter);
    printf("使用的颜色数：%d \n", fi->biClrUsed);
    printf("重要颜色数：%d \n", fi->biClrImporant);
    printf("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n");

    //创建调色板
    int i,j,k=0;
    rgbq *fq = (rgbq *)malloc(256 * sizeof(rgbq));
    for (i = 0; i<256; i++)
    {
        fq[i].rgbBlue = fq[i].rgbGreen = fq[i].rgbRed = i;
    }
    //写入文件头、信息头、调色板
    fwrite(fh, sizeof(fileHeader), 1, fp2);
    fwrite(fi, sizeof(fileInfo), 1, fp2);
    fwrite(fq, sizeof(rgbq), 256, fp2);

    //将位图信息转为灰度
    //存储bmp一行的像素点
    //unsigned char ImgData[900][3];
    unsigned char ImgData[3000][3];
    //将灰度图像存到一维数组中
    //unsigned char grayData2[900];
    unsigned char ImgData2[3000];
    /*
    //错误的算法
    for (i = 0; i < fi->biHeight; i++)
    {
        for (j = 0; j < (fi->biWidth * 3 + 3) / 4 * 4; j++)
        {
            for (k = 0; k < 3; k++)
            {
                fread(&ImgData[j][k], 1, 1, fp1);
            }
        }
        for (j = 0; j < (fi->biWidth + 3) / 4 * 4; j++)
        {
            ImgData2[j] = int((float)ImgData[j][0] * 0.114 +
                (float)ImgData[j][1] * 0.587 +
                (float)ImgData[j][2] * 0.299);
        }

        //将灰度图信息写入
        fwrite(ImgData2, j, 1, fp2);
    }
    */
    /*
    //正确的算法(1)
    for (i = 0; ibiHeight; i++)
    {
        for (j = 0; j<(fi->biWidth + 3) / 4 * 4; j++)
        {
            for (k = 0; k<3; k++)
            fread(&ImgData[j][k], 1, 1, fp1);
        }
        for (j = 0; j<(fi->biWidth + 3) / 4 * 4; j++)
        {
            ImgData2[j] = int((float)ImgData[j][0] * 0.114 +
                (float)ImgData[j][1] * 0.587 +
                (float)ImgData[j][2] * 0.299);
        }
        //将灰度图信息写入
        fwrite(ImgData2, j, 1, fp2);
    }
    */
    //正确算法（2）
    unsigned char * * bmp_data;
    bmp_data = new unsigned char*[fi->biHeight]; //声明一个指针数组
    unsigned char *data288 = new unsigned char[fi->biHeight*fi->biWidth];

    for (i = 0; ibiHeight; i++)
        bmp_data[i] = new unsigned char[(fi->biWidth * 3 + 3) / 4 * 4]; //每个数组元素也是一个指针数组
    for (i = 0; ibiHeight; i++)
        for (j = 0; j<(fi->biWidth * 3 + 3) / 4 * 4; j++)
            fread(&bmp_data[i][j], 1, 1, fp1);//每次只读取一个字节，存入数组

    for (i = 0; ibiHeight; i++)//将24位真彩色转换成灰度图
        for (j = 0; jbiWidth; j++){
        data288[fi->biWidth*i + j] = ((unsigned char)((float)bmp_data[i][3 * j] * 0.114 + (float)bmp_data[i][3 * j + 1] * 0.587 + (float)bmp_data[i][3 * j + 2] * 0.299));
        }

    fwrite(data288, fi->biSizeImage, 1, fp2);
    free(fh);
    free(fi);
    free(fq);
    fclose(fp1);
    fclose(fp2);
    printf("success\n");
    return 0;
}