C语言 将位图文件读入结构

read bitmap file into structure

提问by Ege

I would like to read a bitmap file into a struct and manuplate it like make a mirror effect etc. but I cannot understand which kind of struct should i be creating in order to read into it.

我想将位图文件读入一个结构并对其进行操作，例如制作镜像效果等。但我无法理解我应该创建哪种结构才能读入它。

Thank you for your help

感谢您的帮助

回答by ollo

?This is how you maually load a bmp file

?这是您手动加载 bmp 文件的方式

The bitmap file format: Bitmap file header Bitmap info header palette data Bitmap Dada

位图文件格式： 位图文件头位图信息头调色板数据位图达达

so on with the code part, this is our struct we need to create to hold the bitmap file header

等等代码部分，这是我们需要创建的结构来保存位图文件头

#pragma pack(push, 1)

typedef struct tagBITMAPFILEHEADER
{
    WORD bfType;  //specifies the file type
    DWORD bfSize;  //specifies the size in bytes of the bitmap file
    WORD bfReserved1;  //reserved; must be 0
    WORD bfReserved2;  //reserved; must be 0
    DWORD bfOffBits;  //species the offset in bytes from the bitmapfileheader to the bitmap bits
}BITMAPFILEHEADER;

#pragma pack(pop)

the bftype field checks to see if you are infact loading a bmp file, and if you are the field should be 0x4D42.

bftype 字段检查您是否正在加载 bmp 文件，如果您是该字段，则该字段应为 0x4D42。

Now we need to create our bitmapinfoheader struct. This holds info about our bitmap.

现在我们需要创建我们的 bitmapinfoheader 结构。这包含有关我们位图的信息。

#pragma pack(push, 1)

typedef struct tagBITMAPINFOHEADER
{
    DWORD biSize;  //specifies the number of bytes required by the struct
    LONG biWidth;  //specifies width in pixels
    LONG biHeight;  //species height in pixels
    WORD biPlanes; //specifies the number of color planes, must be 1
    WORD biBitCount; //specifies the number of bit per pixel
    DWORD biCompression;//spcifies the type of compression
    DWORD biSizeImage;  //size of image in bytes
    LONG biXPelsPerMeter;  //number of pixels per meter in x axis
    LONG biYPelsPerMeter;  //number of pixels per meter in y axis
    DWORD biClrUsed;  //number of colors used by th ebitmap
    DWORD biClrImportant;  //number of colors that are important
}BITMAPINFOHEADER;

#pragma pack(pop)

Now on to loading our Bitmap

现在开始加载我们的位图

unsigned char *LoadBitmapFile(char *filename, BITMAPINFOHEADER *bitmapInfoHeader)
{
    FILE *filePtr; //our file pointer
    BITMAPFILEHEADER bitmapFileHeader; //our bitmap file header
    unsigned char *bitmapImage;  //store image data
    int imageIdx=0;  //image index counter
    unsigned char tempRGB;  //our swap variable

    //open filename in read binary mode
    filePtr = fopen(filename,"rb");
    if (filePtr == NULL)
        return NULL;

    //read the bitmap file header
    fread(&bitmapFileHeader, sizeof(BITMAPFILEHEADER),1,filePtr);

    //verify that this is a bmp file by check bitmap id
    if (bitmapFileHeader.bfType !=0x4D42)
    {
        fclose(filePtr);
        return NULL;
    }

    //read the bitmap info header
    fread(bitmapInfoHeader, sizeof(BITMAPINFOHEADER),1,filePtr); // small edit. forgot to add the closing bracket at sizeof

    //move file point to the begging of bitmap data
    fseek(filePtr, bitmapFileHeader.bfOffBits, SEEK_SET);

    //allocate enough memory for the bitmap image data
    bitmapImage = (unsigned char*)malloc(bitmapInfoHeader->biSizeImage);

    //verify memory allocation
    if (!bitmapImage)
    {
        free(bitmapImage);
        fclose(filePtr);
        return NULL;
    }

    //read in the bitmap image data
    fread(bitmapImage,bitmapInfoHeader->biSizeImage,filePtr);

    //make sure bitmap image data was read
    if (bitmapImage == NULL)
    {
        fclose(filePtr);
        return NULL;
    }

    //swap the r and b values to get RGB (bitmap is BGR)
    for (imageIdx = 0;imageIdx < bitmapInfoHeader->biSizeImage;imageIdx+=3) // fixed semicolon
    {
        tempRGB = bitmapImage[imageIdx];
        bitmapImage[imageIdx] = bitmapImage[imageIdx + 2];
        bitmapImage[imageIdx + 2] = tempRGB;
    }

    //close file and return bitmap iamge data
    fclose(filePtr);
    return bitmapImage;
}

Now to make use of all of this:

现在要利用所有这些：

BITMAPINFOHEADER bitmapInfoHeader;
unsigned char *bitmapData;
...
bitmapData = LoadBitmapFile("mypic.bmp",&bitmapInfoHeader);
//now do what you want with it, later on i will show you how to display it in a normal window

Later on ill put up Writing a to bmp and how to load a targa file and how to display them.?

后来生病了写一个到 bmp 以及如何加载 targa 文件以及如何显示它们。？

Quoted from: http://www.vbforums.com/showthread.php?261522-C-C-Loading-Bitmap-Files-%28Manually%29(User: BeholderOf). (Some minor corrections done)

引自：http://www.vbforums.com/showthread.php?261522-CC-Loading-Bitmap-Files-%28Manually%29（用户：BeholderOf）。（做了一些小修正）

回答by Eddy_Em

hereA short working example.

这里是一个简短的工作示例。

It converts a wav-file to bmp (a long ago I had such fun).

它将 wav 文件转换为 bmp（很久以前我玩得很开心）。

Code:

代码：

#include <stdio.h>
#include <strings.h>
#include <sndfile.h>
#include <stdlib.h>
#include <math.h>

#define RATE 44100

typedef struct {
    unsigned short type;                 /* Magic identifier            */
    unsigned int size;                       /* File size in bytes          */
    unsigned int reserved;
    unsigned int offset;                     /* Offset to image data, bytes */
} HEADER;
typedef struct {
    unsigned int size;               /* Header size in bytes      */
    int width,height;                /* Width and height of image */
    unsigned short planes;       /* Number of colour planes   */
    unsigned short bits;         /* Bits per pixel            */
    unsigned int compression;        /* Compression type          */
    unsigned int imagesize;          /* Image size in bytes       */
    int xresolution,yresolution;     /* Pixels per meter          */
    unsigned int ncolours;           /* Number of colours         */
    unsigned int importantcolours;   /* Important colours         */
} INFOHEADER;
typedef struct {
    unsigned char r,g,b,junk;
} COLOURINDEX;


int main(int argc, char *argv[]){
    int i,j,rd;
    int gotindex = 0;
    unsigned char grey,r,g,b;
    double ampl;
    short _2byte[2];
    HEADER header;
    INFOHEADER infoheader;
    COLOURINDEX colourindex[256];
    FILE *fptr; 
    SNDFILE* sndfile = NULL;
    SF_INFO sfinfo;
    long rate = RATE;

    void (*bmpread)();
    void _eightbit(){
        if(fread(&grey, sizeof(unsigned char), 1, fptr) != 1){
        fprintf(stderr,"Image read failed\n");
        exit(-1);
        }
        if (gotindex){
            ampl =  colourindex[grey].r * 64. +
                colourindex[grey].g * 128.+
                colourindex[grey].b * 64.;
        } else {
            ampl = grey * 256. - 32768.;
        }
//      printf("%.2f\n", ampl);
    }
    void _twentyfourbit(){
        do{
            if((rd = fread(&b, sizeof(unsigned char), 1, fptr)) != 1) break;
            if((rd = fread(&g, sizeof(unsigned char), 1, fptr)) != 1) break;
            if((rd = fread(&r, sizeof(unsigned char), 1, fptr)) != 1) break;
        }while(0);
        if(rd != 1){    
            fprintf(stderr,"Image read failed\n");
            exit(-1);
        }
        ampl = r * 64. + g * 128. + b * 64. - 32768.;
//      printf("%.2f\n", ampl);
    }
    if (argc < 3){
        printf("Usage: %s <input.bmp> <output.wav> [samplerate]\n", argv[0]);
        printf("For example:\n\t%s pict.bmp sample.wav 44100 2\n", argv[0]);
        exit(0);
    }
    printf("Input file: %s\n", argv[1]);
    printf("Output file: %s\n", argv[2]);
    if(argc > 3) rate = atoi(argv[3]);
    if(rate < 4000) rate = 4000;
    //if(argc > 4) channels = atoi(argv[4]);        
    sfinfo.samplerate = rate;
    sfinfo.channels = 2;
    sfinfo.format = SF_FORMAT_WAV|SF_FORMAT_PCM_16;
    if((fptr = fopen(argv[1],"r")) == NULL) {
        fprintf(stderr,"Unable to open BMP file \"%s\"\n",argv[1]);
        exit(-1);
    }
        /* Read and check BMP header */
    if(fread(&header.type, 2, 1, fptr) != 1){
        fprintf(stderr, "Failed to read BMP header\n");
        exit(-1);
    }
    if(header.type != 'M'*256+'B'){
        fprintf(stderr, "File is not bmp type\n");
        exit(-1);
    }
    do{
        if((rd = fread(&header.size, 4, 1, fptr)) != 1) break;
        printf("File size: %d bytes\n", header.size);
        if((rd = fread(&header.reserved, 4, 1, fptr)) != 1) break;
        if((rd = fread(&header.offset, 4, 1, fptr)) != 1) break;
        printf("Offset to image data is %d bytes\n", header.offset);
    }while(0);
    if(rd =! 1){
        fprintf(stderr, "Error reading file\n");
        exit(-1);
    }
    /* Read and check the information header */
    if (fread(&infoheader, sizeof(INFOHEADER), 1, fptr) != 1) {
        fprintf(stderr,"Failed to read BMP info header\n");
        exit(-1);
    }
    printf("Image size = %d x %d\n", infoheader.width, infoheader.height);
    printf("Number of colour planes is %d\n", infoheader.planes);
    printf("Bits per pixel is %d\n", infoheader.bits);
    printf("Compression type is %d\n", infoheader.compression);
    printf("Number of colours is %d\n", infoheader.ncolours);
    printf("Number of required colours is %d\n", infoheader.importantcolours);
    /* Read the lookup table if there is one */
    for (i=0; i<255; i++){
        colourindex[i].r = rand() % 256;
        colourindex[i].g = rand() % 256;
        colourindex[i].b = rand() % 256;
        colourindex[i].junk = rand() % 256;
    }
    if (infoheader.ncolours > 0) {
        for (i=0; i<infoheader.ncolours; i++){
            do{
            if ((rd = fread(&colourindex[i].b, sizeof(unsigned char),1,fptr)) != 1)
                break;
            if ((rd = fread(&colourindex[i].g, sizeof(unsigned char),1,fptr)) != 1)
                break;
            if ((rd = fread(&colourindex[i].r, sizeof(unsigned char),1,fptr)) != 1)
                break;
            if ((rd = fread(&colourindex[i].junk, sizeof(unsigned char),1,fptr)) != 1)
                break;
            }while(0);
            if(rd != 1){
                fprintf(stderr,"Image read failed\n");
                exit(-1);
            }           
            printf("%3d\t%3d\t%3d\t%3d\n", i,
            colourindex[i].r, colourindex[i].g, colourindex[i].b);
        }
        gotindex = 1;
    }
    if(infoheader.bits < 8){
        printf("Too small image map depth (%d < 8)\n", infoheader.bits);
        exit(-1);
    }
    /* Seek to the start of the image data */
    fseek(fptr, header.offset, SEEK_SET);
    printf("Creating 16bit WAV %liHz.\n", rate);
    sndfile = sf_open(argv[2], SFM_WRITE, &sfinfo);
    if(sndfile == NULL){
        fprintf(stderr, "Cannot open output file!\n"); exit(-1);
    }
    bmpread = _eightbit;
    if(infoheader.bits == 24)
        bmpread = _twentyfourbit;

    /* Read the image */
    for (j=0;j<infoheader.height;j++) {
        _2byte[1] = 32700;
        for (i=0;i<infoheader.width;i++) {
            bmpread();
            _2byte[0] = (short)ampl;
            sf_write_short(sndfile, _2byte, 2);
            _2byte[1] = 0;
        } // i
    } // j
    fclose(fptr);
    sf_close(sndfile);
}