BMP文件行填充问题

BMP File line padding issue

所以我尝试用 C++ 代码导出一个 .bmp 文件,除了一件主要的事情:行填充,我让它工作。我不是 100% 确定行填充是如何工作的,但我知道我需要它。除了填充之外,我的算法都有效,我在十六进制编辑器中手动将填充添加到导出的图像中并且有效。但是如何添加填充?这是我拥有的:

//Size of the file in bytes
    int fileSize = 54 + (3 * width * height);

    //The sections of the file
    unsigned char generalHeader[14] = {'B','M',0,0, 0,0,0,0, 0,0,54,0, 0,0};
    unsigned char DIBHeader[40]     = {40,0,0,0, 0,0,0,0, 0,0,0,0, 1,0,24,0, 0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0};
    unsigned char pixelArray[1000000];
    unsigned char bmpPad[3] = {0, 0, 0};

    //Set the binary portion of the generalHeader, mainly just file size
    generalHeader[2] = (unsigned char)(fileSize);
    generalHeader[3] = (unsigned char)(fileSize >> 8);
    generalHeader[4] = (unsigned char)(fileSize >> 16);
    generalHeader[5] = (unsigned char)(fileSize >> 24);

    //The binary variable portion of the DIB header
    DIBHeader[4]  = (unsigned char)(width);
    DIBHeader[5]  = (unsigned char)(width >> 8);
    DIBHeader[6]  = (unsigned char)(width >> 16);
    DIBHeader[7]  = (unsigned char)(width >> 24);
    DIBHeader[8]  = (unsigned char)(height);
    DIBHeader[9]  = (unsigned char)(height >> 8);
    DIBHeader[10] = (unsigned char)(height >> 16);
    DIBHeader[11] = (unsigned char)(height >> 24);

    //Loop through all width and height places to add all pixels


    int counter = 0;
    for(short j = height; j >= 0; j--)
    {
        for(short i = 0; i < width; i++)
        {
            //Add all 3 RGB values
            pixelArray[counter] = pixelColour[i][j].red;
            pixelArray[counter] = pixelColour[i][j].green;
            pixelArray[counter] = pixelColour[i][j].blue;
            counter++;
        }
    }

    //Open it
    ofstream fileWorking(fileName);

    //Write the sections
    fileWorking.write((const char*)generalHeader, 14);
    fileWorking.write((const char*)DIBHeader, 40);
    fileWorking.write((const char*)pixelArray, 3 * width * height);

    //NO MEMORY LEAKS 4 ME
    fileWorking.close();

pixelColour 是具有 3 种颜色的结构数据类型,均为 unsigned char 类型。非常感谢任何帮助!

在您的情况下,每行必须是 4 字节(32 位)的倍数。

int pad = 0; // Set pad byte count per row to zero by default.
// Each row needs to be a multiple of 4 bytes.  
if ((width * 3) % 4 != 0) pad = 4 - ((width * 3) % 4); // 4 - remainder(width * 3 / 4).

填充值几乎可以包含任何内容,但最好将它们设置为 0。当您写完每一行时,只需在写之前再写 pad 个零(字节)下一行。

for(short j = height; j >= 0; j--) {
    for(short i = 0; i < width; i++) {
        //Add all 3 RGB values
        pixelArray[counter++] = pixelColour[i][j].red; // Need to advance counter.
        pixelArray[counter++] = pixelColour[i][j].green;
        pixelArray[counter++] = pixelColour[i][j].blue;
    }
    for (int padVal = 0; padVal < pad; padVal++) pixelArray[counter++] = 0; // Pad.
}

最后,你需要写一个更大的文件大小:

fileWorking.write((const char*) pixelArray, (3 * width + pad) * height);