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looking for algorithm to open bmp files

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Hi Does anyone has a c++ algorith to open a bmp file and modify it under Windows XP OS. I will appreciate if you have it if you can share it with e thanks

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bitmap.h :


#include <stdio.h>

#pragma pack(push, structPackSize)
#pragma pack(2)

struct bitmapHeader {

short type;//19778

unsigned int fileSize;
short reserved1;//0

short reserved2;//0

int offsetBits;//118


int infoHeaderSize;//40

int width;
int height;
short planes;//1

short bitCount;
int compression;//0

unsigned int imageSize;
int xPelsPerMeter;//0

int yPelsPerMeter;//0

int colorsUsed;//0

int colorsImportant;//0


#pragma pack(pop, structPackSize)

void initBitmapHeader(bitmapHeader &b, int width, int height, int bitcount);
void printBitmapHeader(bitmapHeader b);
void freadBitmapHeader(FILE *f, bitmapHeader &b);
void fwriteBitmapHeader(FILE *f, bitmapHeader b);
bool freadBitmapData(FILE* f, bitmapHeader b, unsigned char *data);
void fwriteBitmapData(FILE* f, bitmapHeader b, unsigned char* data);


bitmap.cpp :

#include "bitmap.h"

#define PIXELSIZE 3

void initBitmapHeader(bitmapHeader &b, int width, int height, int bitcount)
int padding = (4 - (width*PIXELSIZE)%4)%4;

b.type = 19778;
b.fileSize = (width)*height*(bitcount/8) + padding*height + sizeof(bitmapHeader);
b.reserved1 = 0;
b.reserved2 = 0;
b.offsetBits = sizeof(bitmapHeader);
b.infoHeaderSize = 40;
b.width = width;
b.height = height;
b.planes = 1;
b.bitCount = bitcount;
b.compression = 0;
b.imageSize = (width)*height*(bitcount/8) + padding*height;
b.xPelsPerMeter = 0;
b.yPelsPerMeter = 0;
b.colorsUsed = 0;
b.colorsImportant = 0;

void printBitmapHeader(bitmapHeader b)
"type : %i\n"
"filesize : %i\n"
"reserved1 : %i\n"
"reserved2 : %i\n"
"offsetBits : %i\n"
"infoHeaderSize : %i\n"
"width : %i\n"
"height : %i\n"
"planes : %i\n"
"bitCount : %i\n"
"compression : %i\n"
"imageSize : %i\n"
"xPelPerMeter : %i\n"
"yPelsPerMeter : %i\n"
"colorsUsed : %i\n"
"colorsImportant : %i\n"

void freadBitmapHeader(FILE *f, bitmapHeader &b)
fread(&b.type, 1, sizeof(short), f);
fread(&b.fileSize, 1, sizeof(int), f);
fread(&b.reserved1, 1, sizeof(short), f);
fread(&b.reserved2, 1, sizeof(short), f);
fread(&b.offsetBits, 1, sizeof(int), f);
fread(&b.infoHeaderSize, 1, sizeof(int), f);
fread(&b.width, 1, sizeof(int), f);
fread(&b.height, 1, sizeof(int), f);
fread(&b.planes, 1, sizeof(short), f);
fread(&b.bitCount, 1, sizeof(short), f);
fread(&b.compression, 1, sizeof(int), f);
fread(&b.imageSize, 1, sizeof(int), f);
fread(&b.xPelsPerMeter, 1, sizeof(int), f);
fread(&b.yPelsPerMeter, 1, sizeof(int), f);
fread(&b.colorsUsed, 1, sizeof(int), f);
fread(&b.colorsImportant, 1, sizeof(int), f);

void fwriteBitmapHeader(FILE *f, bitmapHeader b)
fwrite(&b.type, 1, sizeof(short), f);
fwrite(&b.fileSize, 1, sizeof(int), f);
fwrite(&b.reserved1, 1, sizeof(short), f);
fwrite(&b.reserved2, 1, sizeof(short), f);
fwrite(&b.offsetBits, 1, sizeof(int), f);
fwrite(&b.infoHeaderSize, 1, sizeof(int), f);
fwrite(&b.width, 1, sizeof(int), f);
fwrite(&b.height, 1, sizeof(int), f);
fwrite(&b.planes, 1, sizeof(short), f);
fwrite(&b.bitCount, 1, sizeof(short), f);
fwrite(&b.compression, 1, sizeof(int), f);
fwrite(&b.imageSize, 1, sizeof(int), f);
fwrite(&b.xPelsPerMeter, 1, sizeof(int), f);
fwrite(&b.yPelsPerMeter, 1, sizeof(int), f);
fwrite(&b.colorsUsed, 1, sizeof(int), f);
fwrite(&b.colorsImportant, 1, sizeof(int), f);

bool freadBitmapData(FILE* f, bitmapHeader b, unsigned char *data)
unsigned char dummyData[4];
int padding = (b.imageSize-(b.width*b.height*PIXELSIZE))/b.height;
for (int row = 0; row < b.height; row++) {
if (fread(data+(row*(b.width*PIXELSIZE)), 1, b.width*PIXELSIZE, f) != b.width*PIXELSIZE) {
return false;
fread(dummyData, 1, padding, f);
return true;

void fwriteBitmapData(FILE* f, bitmapHeader b, unsigned char* data)
unsigned char dummyData[4] = {0,0,0,0};
int padding = (4 - (b.width*PIXELSIZE)%4)%4;
for (int row = 0; row < b.height; row++) {
fwrite(data+(row*(b.width*PIXELSIZE)), 1, b.width*PIXELSIZE, f);
fwrite(dummyData, 1, padding, f);

to read a bitmap:
FILE* f = ...
bitmapHeader bh;
freadBitmapHeader(f, bh);
unsigned char* data = new unsigned char[bh.imageSize];
freadBitmapData(f, bh, data);

to write a bitmap
FILE* f = ...
bitmapHeader bh;
initBitmapHeader(bh, 320, 240, 24);
fwriteBitmapHeader(f, bh);
fwriteBitmapData(f, bh, data);

PIXELSIZE is defined as 3 in .cpp file, change if you want to work with files other than 24bit images. Manipulate pixels like this:
int index = y*width+x;
data[3*index+0] = red;
data[3*index+1] = green;
data[3*index+2] = blue;

[edited by - zppz on June 7, 2004 3:42:19 AM]

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