從RGB值數組生成BMP文件

Question

我想從已經存儲的RGB值生成一個BMP文件。

我在OS X上進行編程，因此無法使用預定義的BMP標頭。

我嘗試執行以下操作，但預覽顯示文件已損壞。

void bitmap(Image * image) {

typedef struct                       /**** BMP file header structure ****/
{
    unsigned short bfType;           /* Magic number for file */
    unsigned int   bfSize;           /* Size of file */
    unsigned short bfReserved1;      /* Reserved */
    unsigned short bfReserved2;      /* ... */
    unsigned int   bfOffBits;        /* Offset to bitmap data */
} BITMAPFILEHEADER;

typedef struct                       /**** BMP file info structure ****/
{
    unsigned int   biSize;           /* Size of info header */
    int            biWidth;          /* Width of image */
    int            biHeight;         /* Height of image */
    unsigned short biPlanes;         /* Number of color planes */
    unsigned short biBitCount;       /* Number of bits per pixel */
    unsigned int   biCompression;    /* Type of compression to use */
    unsigned int   biSizeImage;      /* Size of image data */
    int            biXPelsPerMeter;  /* X pixels per meter */
    int            biYPelsPerMeter;  /* Y pixels per meter */
    unsigned int   biClrUsed;        /* Number of colors used */
    unsigned int   biClrImportant;   /* Number of important colors */
} BITMAPINFOHEADER;

BITMAPFILEHEADER bfh;
BITMAPINFOHEADER bih;

bfh.bfType = 0x4d42;
bfh.bfReserved1 = 0;
bfh.bfReserved2 = 0;
bfh.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
bfh.bfOffBits = 0x36;

bih.biSize = sizeof(BITMAPINFOHEADER);
bih.biWidth = image->getWidth();
bih.biHeight = image->getHeight();
bih.biPlanes = 1;
bih.biBitCount = 24;
bih.biCompression = 0;
bih.biSizeImage = 0;
bih.biXPelsPerMeter = 0x0ec4;
bih.biYPelsPerMeter = 0x0ec4;
bih.biClrUsed = 0;
bih.biClrImportant = 0;

FILE *file = fopen("a.bmp", "wb");
if (!file) {
    cout << "File not found";
    return;
}

fwrite(&bfh, 1, sizeof(bfh), file);
fwrite(&bih, 1, sizeof(bfh), file);

for (int x = 0; x < image->getWidth(); x++) {
    for (int y = 0; y < image->getHeight(); y++) {
        float r = image->getPixel(x, y).r;
        float g = image->getPixel(x, y).g;
        float b = image->getPixel(x, y).b;
        fwrite(&r, 1, 1, file);
        fwrite(&g, 1, 1, file);
        fwrite(&b, 1, 1, file);
    }
}
}

我不確定我是否正確理解結構。 我已經嘗試閱讀有關它的內容，但是我一定會丟失一些東西。

這是文件的十六進制輸出

42 4D 00 02 38 00 00 00 00 00 00 36 00 00 00 28 00 00 00 80 02 00 00 E0 01 00 00 01 00 18 00 00 00 00 00 00 00 00 00 C4 0E 00 00 C4 0E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0 0 0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Answer 1

這個問題很好，因為它啟發了一些陷阱。 這是您代碼中的所有問題。 通過修復它們，一切都會按預期工作：

• 您的bfSize字段不包括位圖的大小

• 常規： BITMAPFILEHEADER變大，因為它以2字節值開頭，然后是4字節值。 填充規則說，此結構的第一個字段將是4個字節而不是2個字節。解決方案：通過從BITMAPFILEHEADER排除魔術數字來單獨寫入魔術數字：

   unsigned short magic=0x4d42; //This field is _not_ included in `BITMAPFILEHEADER` fwrite(&magic,1,sizeof(magic),file); // Write the remaining part of the header (if you did not get an I/O error...) 

  此修改還意味着BITMAPFILEHEADER::bfSize為2+sizeof(BITMAPFILEHADER) + sizeof(BITMAPINFOHEADER)+ biWidth*biHeight*3

• 您還通過了bfh和bih展位的sizeof(bfh) ，因此永遠不會編寫完整的BITMAPINFOHEADER

• BMP文件格式要求每條掃描線都是DWORD對齊的，因此根據寬度，您可能需要在每條掃描線后寫入零字節

• 如果您認為第一條掃描線朝上，則圖像為上下顛倒，因為您的身高為正。

• 位圖文件按行存儲，因此您應該在最內部的循環中遍歷x坐標

• 您還寫入了錯誤的像素值。 您應該寫unsigned char而不是float。 您寫入正確的大小（1個字節），但它不是正確的值：

   unsigned char r = image->getPixel(x, y).r/255; //If 1.0f is white. 

  同樣，位圖是BGR（A）而不是RGB（A）。

假設您的寬度不錯，一個有效的例子是

void bitmap()
{
typedef struct                       /**** BMP file header structure ****/
    {
    unsigned int   bfSize;           /* Size of file */
    unsigned short bfReserved1;      /* Reserved */
    unsigned short bfReserved2;      /* ... */
    unsigned int   bfOffBits;        /* Offset to bitmap data */
    } BITMAPFILEHEADER;

typedef struct                       /**** BMP file info structure ****/
    {
    unsigned int   biSize;           /* Size of info header */
    int            biWidth;          /* Width of image */
    int            biHeight;         /* Height of image */
    unsigned short biPlanes;         /* Number of color planes */
    unsigned short biBitCount;       /* Number of bits per pixel */
    unsigned int   biCompression;    /* Type of compression to use */
    unsigned int   biSizeImage;      /* Size of image data */
    int            biXPelsPerMeter;  /* X pixels per meter */
    int            biYPelsPerMeter;  /* Y pixels per meter */
    unsigned int   biClrUsed;        /* Number of colors used */
    unsigned int   biClrImportant;   /* Number of important colors */
    } BITMAPINFOHEADER;

BITMAPFILEHEADER bfh;
BITMAPINFOHEADER bih;

/* Magic number for file. It does not fit in the header structure due to alignment requirements, so put it outside */
unsigned short bfType=0x4d42;           
bfh.bfReserved1 = 0;
bfh.bfReserved2 = 0;
bfh.bfSize = 2+sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER)+640*480*3;
bfh.bfOffBits = 0x36;

bih.biSize = sizeof(BITMAPINFOHEADER);
bih.biWidth = 640;
bih.biHeight = 480;
bih.biPlanes = 1;
bih.biBitCount = 24;
bih.biCompression = 0;
bih.biSizeImage = 0;
bih.biXPelsPerMeter = 5000;
bih.biYPelsPerMeter = 5000;
bih.biClrUsed = 0;
bih.biClrImportant = 0;

FILE *file = fopen("a.bmp", "wb");
if (!file)
    {
    printf("Could not write file\n");
    return;
    }

/*Write headers*/
fwrite(&bfType,1,sizeof(bfType),file);
fwrite(&bfh, 1, sizeof(bfh), file);
fwrite(&bih, 1, sizeof(bih), file);

/*Write bitmap*/
for (int y = bih.biHeight-1; y>=0; y--) /*Scanline loop backwards*/
    {
    for (int x = 0; x < bih.biWidth; x++) /*Column loop forwards*/
        {
        /*compute some pixel values*/
        unsigned char r = 255*((float)x/bih.biWidth);
        unsigned char g = 255*((float)y/bih.biHeight);
        unsigned char b = 0;
        fwrite(&b, 1, 1, file);
        fwrite(&g, 1, 1, file);
        fwrite(&r, 1, 1, file);
        }
    }
fclose(file);
}

Answer 2

user877329的代碼對我有用。 （因為我使用C語言，所以進行了一些小的更改）注意：請注意變量的“大小”，因為變量的大小可能不同，具體取決於您編譯的平台。