C++ 位图到 base64

Question

我有以下代码来创建位图：

//raw data
PBYTE firstPixel = (PBYTE)((PBYTE)AnsiBdbRecord) + sizeof(WINBIO_BDB_ANSI_381_RECORD);

// declare other bmp structures
BITMAPFILEHEADER bmfh;
BITMAPINFOHEADER info;
RGBQUAD rq[256];
// create the grayscale palette 
for (int i = 0; i<256; i++)
{
    rq[i].rgbBlue = i;
    rq[i].rgbGreen = i;
    rq[i].rgbRed = i;
    rq[i].rgbReserved = 0;
}
//RGBQUAD bl = { 0,0,0,0 };  //black color
//RGBQUAD wh = { 0xff,0xff,0xff,0xff }; // white color

// andinitialize them to zero
memset(&bmfh, 0, sizeof(BITMAPFILEHEADER));
memset(&info, 0, sizeof(BITMAPINFOHEADER));

// fill the fileheader with data
bmfh.bfType = 0x4d42; // 0x4d42 = 'BM'
bmfh.bfReserved1 = 0;
bmfh.bfReserved2 = 0;
bmfh.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER); // + padding;
bmfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD);

// fill the infoheader
info.biSize = sizeof(BITMAPINFOHEADER);
info.biWidth = Width;
info.biHeight = Height;
info.biPlanes = 1; // we only have one bitplane
info.biBitCount = PixelDepth; // RGB mode is 24 bits
info.biCompression = BI_RGB;
info.biSizeImage = 0; // can be 0 for 24 bit images
info.biXPelsPerMeter = 0x0ec4; // paint and PSP use this values
info.biYPelsPerMeter = 0x0ec4;
info.biClrUsed = 0; // we are in RGB mode and have no palette
info.biClrImportant = 0; // all colors are importantenter code here

并且我保存如下：

    HANDLE file = CreateFile(bmpfile, GENERIC_WRITE, FILE_SHARE_READ,
    NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (file == NULL)
{
    DWORD dw = GetLastError();
    CloseHandle(file);
}

// write file header
if (WriteFile(file, &bmfh, sizeof(BITMAPFILEHEADER), &bwritten, NULL) == false)
{
    DWORD dw = GetLastError();
    CloseHandle(file);
}
// write infoheader
if (WriteFile(file, &info, sizeof(BITMAPINFOHEADER), &bwritten, NULL) == false)
{
    DWORD dw = GetLastError();
    CloseHandle(file);
}
//write rgbquad for black
if (WriteFile(file, &rq, sizeof(rq), &bwritten, NULL) == false)
{
    DWORD dw = GetLastError();
    CloseHandle(file);
}
// write image data
if (WriteFile(file, &firstPixel[0], imageSize, &bwritten, NULL) == false)
{
    DWORD dw = GetLastError();
    CloseHandle(file);
}

// and clean up
CloseHandle(file);

我认为以上是保存位图图像的标准方式。但是，我不想保存图像，而是希望它以 BASE64 的形式可用并在 HTTP Post 中传递。因此，这个问题涉及this one, but I am having a lot of difficulties converting the bmp structure to BASE64. I have taken the BASE64 encoder from here，但我不知道如何将BMPFILEHEADER、BMPINFOHEADER、RGBQUAD和原始数据结构作为参数传递给BASE64编码器。

关于如何组合我收集的信息有什么想法或建议吗？

更新

感谢 Roman Pustylnikov，我已经走得更远了：我正在创建这样的结构：

    struct ImageBuffer
{
    BITMAPFILEHEADER bfheader;
    BITMAPINFOHEADER infobmp;
    RGBQUAD rgb[256];
    PBYTE bitmap;
};

填写如下：

ImageBuffer capture;
capture.bfheader = bmfh;
capture.infobmp = info;
// create the grayscale palette 
for (int i = 0; i<256; i++)
{
    capture.rgb[i].rgbBlue = i;
    capture.rgb[i].rgbGreen = i;
    capture.rgb[i].rgbRed = i;
    capture.rgb[i].rgbReserved = 0;
}
capture.bitmap = firstPixel;

并进行如下转换：

int totalSize = sizeof(capture.bfheader) + sizeof(capture.infobmp) + sizeof(capture.rgb) + imageSize;
std::string encodedImage = base64_encode(reinterpret_cast<const unsigned char*>(&capture), totalSize);

但是，它给了我一个无效的位图。此外，当我从磁盘（使用 writefile 生成的位图）加载位图时，我得到了一个不同的 base64 字符串。我使用 C# 代码比较两个 Base64 字符串：

            // generated base64 string
        string test = "Put base64string generated from C++ here";
        byte[] imageBytes = Convert.FromBase64String(test);

        // generate the same string based on the actual bmp
        byte[] data = File.ReadAllBytes(@"c:\successtest.bmp");
        string original = Convert.ToBase64String(data);

更新二：解决方案

解决办法可以在最新更新的Roman Pustylnikov的回答中找到。

Answer 1

你可以不用 file in the middle, using the following example 作为 encoder/decoder:

第一种方法是创建连续内存并将其作为输入：

int size=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD)*256 + imageSize ;

   unsigned char * bmpBuff = new char[size];
   int i = 0;
   memcpy((void *)( &( bmpBuff[i] )), (void *) &bfheader,sizeof(BITMAPFILEHEADER) );
   i+=sizeof(BITMAPFILEHEADER);
   memcpy((void *)( &( bmpBuff[i] )), (void *) &infobmp,sizeof(BITMAPINFOHEADER) );
   i+=sizeof(BITMAPINFOHEADER);
   memcpy((void *)( &( bmpBuff[i] )), (void *) &rq,sizeof(RGBQUAD)*256 );
   i+=sizeof(RGBQUAD)*256;
   memcpy((void *)( &( bmpBuff[i] )), (void *) firstPixel, imageSize );
   std::string encodedImage = base64_encode(bmpBuff, size);

这种方法的缺点是需要复制内存。

另一种方法是处理"lost triplet"。为此，我们需要定义一个结构：

struct ScreenShotBuffer
{
    BITMAPFILEHEADER bfheader;
    BITMAPINFO infobmp;
    RGBQUAD rgb[256];      
};

棘手的部分来了。由于编码处理字节的三元组，因此您需要处理两个缓冲区之间的边界（我没有对此进行测试，因此它可能包含错误，只是一种通用方法）。

int size=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD)*256;


unsigned char *info = einterpret_cast<const unsigned char*> &screenshotInfo;
unsigned char *img = einterpret_cast<const unsigned char*> firstPixel;

std::string encodedInfo = base64_encode(info , size);
std::string encodedLostTriplet = "";

int offset = size%3;

unsigned char lostTriplet[3];
   if (offset) {
     lostTriplet[0]=info[size-offset];
     if (offset==2) 
         lostTriplet[1] = info[size-offset+1];
     else
         lostTriplet[1] = img[0];
     lostTriplet[2] = img[2-offset];
     encodedLostTriplet = base64_encode(lostTriplet, 3);
   }
   else {
      offset=3;
   }

std::string encodedData = base64_encode(reinterpret_cast<const unsigned char*> &img[3-offset], imageSize - (3 - offset) );

std::string encodedImage = encodedInfo + lostTriplet + encodedData;

有点乱，但应该在相同的内存上工作。

C++ 位图到 base64

C++ bitmap to base64

c++

bitmap

biometrics

更新

更新二：解决方案