Read bitmap file into structure
Solution 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)
Solution 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);
}
Ege
Updated on June 14, 2021Comments
-
Ege almost 3 years
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.
-
Agent_L over 11 yearsYou forgot about structure packing. Using
WORD
in struct paired with binary read on 32-bit (or more) system is asking for trouble. -
ollo over 11 yearsYou mean adding
#pragma pack(push,1)
is required? -
Agent_L over 11 yearsAbsolutelly. Either pragma, or setting globally for project. Otherwise you have no idea how far
bfReserved1
andbfReserved2
are apart. Maybe 2 bytes (as you intended), maybe 4, maybe else. -
ollo over 11 yearsThanks! Added pragma's for the structs.
-
Agent_L over 11 yearsI just learned it should work in GCC too : gcc.gnu.org/onlinedocs/gcc/Structure_002dPacking-Pragmas.html (I thought it was Microsoft-specific feature)
-
ollo over 11 yearsWith gcc you can use packed attribute instead too:
__attribute__((__packed__))
(see: gcc.gnu.org/onlinedocs/gcc-3.1.1/gcc/Type-Attributes.html) -
Agent_L over 11 yearsAnother approach would be to read entire file into a buffer and THEN cast the buffer ptr into struct ptr. It's useful when dealing with several formats, so one can match several types while loading only once. The dummy array at the end of BITMAPINFO takes advantage of this. Using
bfOffBits
is way simplier then. -
Ege over 11 yearsThank you very much sir very appreciated it. It would be great if you could put up some examples like rotate or mirror for basic examples.
-
Andon M. Coleman about 10 years
free
ingbitmapImage
when it is 0 in this code makes no sense whatsoever. -
Daniel Marschall almost 9 yearsFor a good coding style, shouldn't
malloc
be called in the same method as itsfree
counterpart (i.e. outside of this bitmap read method)? -
Ofer Magen almost 8 yearswhat about the color array? sometimes when there are few colors the data table doesn't contain the rgb but a set of numbers described at the beginning you didn't mentioned that
-
Malcolm McLean over 7 yearsYou need to read the binary file portably. Portable read routines are here github.com/MalcolmMcLean/ieee754/blob/master/binaryio.c and, though the integer routines are simple, they are maybe not obvious. A portable BMP format reader is here github.com/MalcolmMcLean/babyxrc/blob/master/src/bmp.c
-
Eddy_Em over 7 years@MalcolmMcLean your code is very slow. Better example is here. Also your code isn't portable as instead of fixed types like int64_t, uint32_t etc it use int/short etc. Try it on 8/16 or 32-bit architecture!
-
Malcolm McLean over 7 yearsThat code isn't portable. If you have a guaranteed bit width type, it's reasonable to use it. But it's not solving the problem, just hardcoding it in. Mine will work with any size of int above 16 bits, so on any conforming C compiler.
-
DevZer0 over 6 yearsfor the header alignment issue i find its much cleaner to just read the first 2 bytes into a pointer of its own, validate the type and then load the next 4 integers into a header struct. then you don't need to rely on #pragma
-
kenmux over 6 yearsPlease note that there's a mismatch: struct
BITMAPINFOHEADER
hasbOffBits
, but in the functionLoadBitmapFile()
you usebfOffBits
. Maybe all usebfOffBits
? -
jumpjack almost 6 yearsI found an amazing free hex editor which allows directly importing c-style structures and applying them to a file: FlexHex. Then, a window show which values each field is set to. But I have yet to figure out if it supports also offset structures...
-
phoenixstudio over 3 yearsis the link to your github necessary ?
-
Lovish Garg over 3 yearsThere are more than one file in my project and what's wrong if I give link to my github. In fact its better because I have uploaded a detailed README and there are differnet files for different works and if anyone wants to run that BMP program on its system then he/she can simply fork the repository.