Question

I have an array of raw bytes and I want to make a bmp file from those bytes. That is, I have to fill bitmap header structre and other things, then write down the bytes so I have a bmp file in the proper format.

As I need this for some quick check only, I wonder if there is a portable method to do this – take raw bytes and save them as a bmp file. Any Windows version won’t do as I’m writing that on Unix.

Alternatively, I can save those bytes as any other image format – I only need to have a quick look at the resulting picture.

Answer 1

The following will give you a .ppm image from a byte array. The "P6" specifies binary format 3 byte per pixel, but plain text is also supported and various forms of grayscale. The reason you should use this is that it is easy as can be and most *nix systems have a bunch of ppmto*-tools: ppmtobmp, ppmtojpeg, …, ppmtopng… you name it.

typedef struct {
    int width;
    int height;
    uint8_t *data;
    size_t size;
} ppm_image;

size_t ppm_save(ppm_image *img, FILE *outfile) {
    size_t n = 0;
    n += fprintf(outfile, "P6\n# THIS IS A COMMENT\n%d %d\n%d\n", 
                 img->width, img->height, 0xFF);
    n += fwrite(img->data, 1, img->width * img->height * 3, outfile);
    return n;
}

There is also ppmtocad… who would have guessed?