Read bitmap file into structure

Question

I would like to read a bitmap file into a struct and manipulate it like eg. making a mirror effect, but I cannot understand which kind of struct should I be creating in order to read into it.

Thank you for your help.

Answer 1

»This is how you manually load a .BMP file

The bitmap file format:

• Bitmap file header
• Bitmap info header
• Palette data
• Bitmap data

So on with the code part. This is our struct we need to create to hold the bitmap file header.

#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;  //specifies the offset in bytes from the bitmapfileheader to the bitmap bits }BITMAPFILEHEADER;  #pragma pack(pop) 

The bftype field checks to see if you are in fact loading a .BMP file, and if you are, the field should be 0x4D42.

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

#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;  //specifies height in pixels     WORD biPlanes;  //specifies the number of color planes, must be 1     WORD biBitCount;  //specifies the number of bits per pixel     DWORD biCompression;  //specifies 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 the bitmap     DWORD biClrImportant;  //number of colors that are important }BITMAPINFOHEADER;  #pragma pack(pop) 

Now on to loading our bitmap.

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 file 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 checking bitmap id     if (bitmapFileHeader.bfType !=0x4D42)     {         fclose(filePtr);         return NULL;     }      //read the bitmap info header     fread(bitmapInfoHeader, sizeof(BITMAPINFOHEADER),1,filePtr);       //move file pointer to the beginning 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,1,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)     {         tempRGB = bitmapImage[imageIdx];         bitmapImage[imageIdx] = bitmapImage[imageIdx + 2];         bitmapImage[imageIdx + 2] = tempRGB;     }      //close file and return bitmap image data     fclose(filePtr);     return bitmapImage; } 

Now to make use of all of this:

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 I'll put up Writing to a .BMP, and how to load a targa file, and how to display them.«

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

Answer 2

here A short working example.

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

Code:

#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); }