generate monochrome bitmap image using c - c

Question

I am writing code to generate monochrome bmp image out of array. there are plenty of tools to generate bmp to array but i want it in reverse way. i found lots of code but it was color image.
here is code i am trying...
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <malloc.h>
#define _height 64
#define _width 128
#define _bitsperpixel 1
#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 0x55
#pragma pack(push,1)
unsigned char arr[8192]={0};
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[]) {
int i;
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);
for(i=0;i<8192;i++)
{
pixelbuffer[i] = arr[i];
}
// memset(pixelbuffer,pixel,_pixelbytesize);
fwrite(pixelbuffer,1,_pixelbytesize,fp);
fclose(fp);
free(pbitmap);
free(pixelbuffer);
}
i am giving bits per pixel is 1 bit (i want either black or white), and not sure about other parameters which has to be change.
if i use _bitsperpixel as 24 then it is working properly but if i assign as 1 then getting it is getting crashed..

Answer 1

When _bitsperpixel == 1, then _pixelbytesize == 1024. Your loop runs till 8192, thus writing beyond the allocated memory.
Depending on what you store in your arr, you should either reduce the number of iterations of the loop to _pixelbytesize, or convert your bytes in arr into bits:
for(int i = 0; i < _pixelbytesize; ++i)
{
uint8_t b = 0;
for(int j = 0; j < 8; ++j)
b |= arr[8*i + j] >> 7 << j;
pixelbuffer[i] = b;
}
Note that this is a simple code that works only for image widths that are divisible by eight.