Color changing bmp in c - c

Question

I have a pixel information array who has the biSizeImage size and contains triplets of the form (blue, green, red) with values ​​between 0 and 255. I must change my bmp color from red, to white, but i have a problem, as can be seen in picture.
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
int main()
{
BITMAPFILEHEADER file;
BITMAPINFOHEADER info;
FILE* f=fopen("imagine.bmp","rb");
fread(&file,sizeof(BITMAPFILEHEADER),1,f);
fread(&info,sizeof(BITMAPINFOHEADER),1,f);
RGBQUAD *a=malloc(info.biSizeImage*sizeof(RGBQUAD));
fread(a,sizeof(RGBQUAD),info.biSizeImage,f);
for(int i=0;i<info.biSizeImage;i++)
{
a[i].rgbBlue=255;
a[i].rgbGreen=255;
a[i].rgbRed=255;
}
FILE* f2=fopen("imagine2.bmp","wb");
if(f2==NULL)
printf("Error");
fwrite(&file,sizeof(BITMAPFILEHEADER),1,f2);
fwrite(&info,sizeof(BITMAPINFOHEADER),1,f2);
fwrite(a,sizeof(RGBQUAD),info.biSizeImage,f2);
return 0;
Output
Original image

Answer 1

info.biSizeImage can be zero. Check to make sure it is not zero, or calculate it based on stride. Width, height, and bitcount values are always set.
As noted in comments, 24 bit image has 3 bytes (24 bit) per pixel. RGBQUA is for 32-bit image. You have to iterate through the height, and then width 3 bytes at a time.
int main(void)
{
BITMAPFILEHEADER file;
BITMAPINFOHEADER info;
FILE* f = fopen("imagine.bmp", "rb");
fread(&file, sizeof(BITMAPFILEHEADER), 1, f);
fread(&info, sizeof(BITMAPINFOHEADER), 1, f);
if(info.biBitCount != 24)
return 0;
int stride = ((info.biWidth * info.biBitCount + 31) / 32) * 4;
int size = stride * info.biHeight;
BYTE *a = malloc(stride * info.biHeight);
fread(a, 1, size, f);
for(int y = info.biHeight - 1; y >= 0; y--)
{
for(int x = 0; x < stride; x += 3)
{
int i = y * stride + x;
a[i + 0] = 255;
a[i + 1] = 255;
a[i + 2] = 255;
}
}
FILE* f2 = fopen("imagine2", "wb");
if(f2 == NULL)
printf("Error");
fwrite(&file, sizeof(BITMAPFILEHEADER), 1, f2);
fwrite(&info, sizeof(BITMAPINFOHEADER), 1, f2);
fwrite(a, 1, size, f2);
return 0;
}