在C中创建BMP文件(位图)

Question

我正试图在C中创建一个位图,只是来自代码.我目前正在尝试制作一个非常简单的.bmp图像,高度为1像素,宽度为4像素,所有白色像素.我已阅读格式说明并尝试应用它.这导致以下代码:

char bitmap[1000];

void BMPmake()
{
    // -- FILE HEADER -- //

    // bitmap signature
    bitmap[0] = 'B';
    bitmap[1] = 'M';

    // file size
    bitmap[2] = 66; // 40 + 14 + 12
    bitmap[3] = 0;
    bitmap[4] = 0;
    bitmap[5] = 0;

    // reserved field (in hex. 00 00 00 00)
    for(int i = 6; i < 10; i++) bitmap[i] = 0;

    // offset of pixel data inside the image
    for(int i = 10; i < 14; i++) bitmap[i] = 0;

    // -- BITMAP HEADER -- //

    // header size
    bitmap[14] = 40;
    for(int i = 15; i < 18; i++) bitmap[i] = 0;

    // width of the image
    bitmap[18] = 4;
    for(int i = 19; i < 22; i++) bitmap[i] = 0;

    // height of the image
    bitmap[22] = 1;
    for(int i = 23; i < 26; i++) bitmap[i] = 0;

    // reserved field
    bitmap[26] = 1;
    bitmap[27] = 0;

    // number of bits per pixel
    bitmap[28] = 24; // 3 byte
    bitmap[29] = 0;

    // compression method (no compression here)
    for(int i = 30; i < 34; i++) bitmap[i] = 0;

    // size of pixel data
    bitmap[34] = 12; // 12 bits => 4 pixels
    bitmap[35] = 0;
    bitmap[36] = 0;
    bitmap[37] = 0;

    // horizontal resolution of the image - pixels per meter (2835)
    bitmap[38] = 0;
    bitmap[39] = 0;
    bitmap[40] = 0b00110000;
    bitmap[41] = 0b10110001;

    // vertical resolution of the image - pixels per meter (2835)
    bitmap[42] = 0;
    bitmap[43] = 0;
    bitmap[44] = 0b00110000;
    bitmap[45] = 0b10110001;

    // color pallette information
    for(int i = 46; i < 50; i++) bitmap[i] = 0;

    // number of important colors
    for(int i = 50; i < 54; i++) bitmap[i] = 0;

    // -- PIXEL DATA -- //
    for(int i = 54; i < 66; i++) bitmap[i] = 0;
}

void BMPwrite()
{
    FILE *file;
    file = fopen("bitmap.bmp", "w+");
    for(int i = 0; i < 66; i++)
    {
        fputc(bitmap[i], file);
    }
    fclose(file);
}

当我尝试打开此图像时,它表示图像已损坏.我在这里错过了什么吗？

我还注意到.bmp整数的编码是小端.我认为这意味着我必须颠倒字节的顺序.例如,四个字节中的256个是:00000000 00000000 00000001 00000000,我认为在小端,这将是:00000000 00000001 00000000 00000000

任何人都可以帮我一把吗？我使用正确的方法吗？任何帮助,将不胜感激!

提前致谢!

Answer 1

您的像素偏移量(字节10..13)为零,但像素数据实际上并不从文件的开头开始,而是从字节54开始.

也:

• 你对字节34的评论是"位",但是意思是"字节",但当然这并不重要.

• 您的水平和垂直分辨率具有错误的字节顺序,但我非常怀疑这一点很重要.

如果我这样做,我会为头数据定义结构(事实上,如果你在Windows上,微软已经这样做了)并使用宏或其他东西将字节顺序放入正确的顺序.

是否"必须颠倒字节的顺序"取决于您正在使用的处理器的字节顺序.分别编写单独的字节,就像你正在做的那样,是避免担心这一点的有效方法.

Answer 2

这是在linux上测试的代码.

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <malloc.h>
#define _height 600
#define _width 800
#define _bitsperpixel 24
#define _planes 1
#define _compression 0
#define _pixelbytesize _height*_width*_bitsperpixel/8
#define _filesize _pixelbytesize+sizeof(bitmap)
#define _xpixelpermeter 0x130B //2835 , 72 DPI
#define _ypixelpermeter 0x130B //2835 , 72 DPI
#define pixel 0xFF
#pragma pack(push,1)
typedef struct{
    uint8_t signature[2];
    uint32_t filesize;
    uint32_t reserved;
    uint32_t fileoffset_to_pixelarray;
} fileheader;
typedef struct{
    uint32_t dibheadersize;
    uint32_t width;
    uint32_t height;
    uint16_t planes;
    uint16_t bitsperpixel;
    uint32_t compression;
    uint32_t imagesize;
    uint32_t ypixelpermeter;
    uint32_t xpixelpermeter;
    uint32_t numcolorspallette;
    uint32_t mostimpcolor;
} bitmapinfoheader;
typedef struct {
    fileheader fileheader;
    bitmapinfoheader bitmapinfoheader;
} bitmap;
#pragma pack(pop)

int main (int argc , char *argv[]) {
    FILE *fp = fopen("test.bmp","wb");
    bitmap *pbitmap  = (bitmap*)calloc(1,sizeof(bitmap));
    uint8_t *pixelbuffer = (uint8_t*)malloc(_pixelbytesize);
    strcpy(pbitmap->fileheader.signature,"BM");
    pbitmap->fileheader.filesize = _filesize;
    pbitmap->fileheader.fileoffset_to_pixelarray = sizeof(bitmap);
    pbitmap->bitmapinfoheader.dibheadersize =sizeof(bitmapinfoheader);
    pbitmap->bitmapinfoheader.width = _width;
    pbitmap->bitmapinfoheader.height = _height;
    pbitmap->bitmapinfoheader.planes = _planes;
    pbitmap->bitmapinfoheader.bitsperpixel = _bitsperpixel;
    pbitmap->bitmapinfoheader.compression = _compression;
    pbitmap->bitmapinfoheader.imagesize = _pixelbytesize;
    pbitmap->bitmapinfoheader.ypixelpermeter = _ypixelpermeter ;
    pbitmap->bitmapinfoheader.xpixelpermeter = _xpixelpermeter ;
    pbitmap->bitmapinfoheader.numcolorspallette = 0;
    fwrite (pbitmap, 1, sizeof(bitmap),fp);
    memset(pixelbuffer,pixel,_pixelbytesize);
    fwrite(pixelbuffer,1,_pixelbytesize,fp);
    fclose(fp);
    free(pbitmap);
    free(pixelbuffer);
}