BMP文件行填充问题

BMP File line padding issue

本文关键字：问题 填充 文件 BMP      更新时间：2023-10-16

所以我试图用C++代码导出一个.bmp文件，除了一件主要的事情：换行之外，我已经让它正常工作了。我不能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，我的算法也能工作，我在十六进制编辑器中手动将填充添加到我导出的图像中，它也能工作。但是我该如何添加填充？这是我所拥有的：

//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，所有类型都是无符号字符。非常感谢您的帮助！

在您的情况下，每行必须是4个字节（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。当写入每一行时，只需在写入下一行之前再写入pad个零（字节）。

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，您需要编写一个更大的文件大小：

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