C++: Convert text file of integers into a bitmap image file in BMP format

Question

I have a text file being saved by a matrix library containing a 2D matrix as such:

1 0 0 
6 0 4
0 1 1

Where each number is represented with

Answer 1

To output a readable BMP file, you need to put a header first:

#include 

DWORD dwSizeInBytes = rows*cols*4; // when your matrix contains RGBX data)

// fill in the headers
BITMAPFILEHEADER bmfh;
bmfh.bfType = 0x4D42; // 'BM'
bmfh.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + dwSizeInBytes;
bmfh.bfReserved1 = 0;
bmfh.bfReserved2 = 0;
bmfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

BITMAPINFOHEADER bmih;
bmih.biSize = sizeof(BITMAPINFOHEADER);
bmih.biWidth = cols;
bmih.biHeight = rows;
bmih.biPlanes = 1;
bmih.biBitCount = 32;
bmih.biCompression = BI_RGB;
bmih.biSizeImage = 0;
bmih.biXPelsPerMeter = 0;
bmih.biYPelsPerMeter = 0;
bmih.biClrUsed = 0;
bmih.biClrImportant = 0;

Now before you write your color information, just write the bitmap header

fwrite(&bmfh, sizeof(bmfh),1, bmp_ptr);
fwrite(&bmih, sizeof(bmih),1, bmp_ptr);

And finally the color information:

fwrite(&intmatrix, size, sizeof(int), bmp_ptr);

Note, that the block size is sizeof(int), as your matrix doesn't contain single characters, but integers for each value. Depending on the content of your matrix, it might be a good idea to convert the values to COLORREF values (Check the RGB macro, which can be found in WinGDI.h, too)