Invalid or Unsupported Image Format (Recover)

Question

// Copies a BMP file

#include <stdio.h>
#include <stdlib.h>

#include "bmp.h"

int main(int argc, char *argv[])
{

int n = atoi(argv[1]);
// ensure proper usage
if (argc != 4 || (n > 100 || n < 0))
{
    fprintf(stderr, "Usage: copy infile outfile\n");
    return 1;
}

// remember filenames
char *infile = argv[2];
char *outfile = argv[3];

// open input file
FILE *inptr = fopen(infile, "r");
if (inptr == NULL)
{
    fprintf(stderr, "Could not open %s.\n", infile);
    return 2;
}

// open output file
FILE *outptr = fopen(outfile, "w");
if (outptr == NULL)
{
    fclose(inptr);
    fprintf(stderr, "Could not create %s.\n", outfile);
    return 3;
}

// read infile's BITMAPFILEHEADER
BITMAPFILEHEADER bf;
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

// read infile's BITMAPINFOHEADER
BITMAPINFOHEADER bi;
fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);

// ensure infile is (likely) a 24-bit uncompressed BMP 4.0
if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 ||
    bi.biBitCount != 24 || bi.biCompression != 0)
{
    fclose(outptr);
    fclose(inptr);
    fprintf(stderr, "Unsupported file format.\n");
    return 4;
}

// determine padding for scanlines
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

// stores the original biWidth and biHeight in variables
int originalbiWidth = bi.biWidth;
int originalbiHeight = bi.biHeight;

// multiplies the biWidth and biHeight by n
bi.biWidth *= n;
bi.biHeight *= n;

// determines padding for scanlines after they are scaled by a factor of n
int outputPadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

bi.biSizeImage = (bi.biWidth * sizeof(RGBTRIPLE) + outputPadding) * abs(bi.biHeight);
bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

// write outfile's BITMAPFILEHEADER
fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);

// write outfile's BITMAPINFOHEADER
fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);


// iterate over infile's scanlines
for (int i = 0, biHeight = abs(originalbiHeight); i < biHeight; i++)
{
    // iterate over pixels in scanline
    for (int j = 0; j < originalbiWidth; j++)
    {
        // temporary storage
        RGBTRIPLE triple;

        // read RGB triple from infile
        fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

        for (int k = 0; k < n; k++)
        {
            // write RGB triple to outfile
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
        }

    }

    // skip over padding, if any
    fseek(inptr, padding, SEEK_CUR);

    // then add it back (to demonstrate how)
    for (int k = 0; k < outputPadding; k++)
    {
        fputc(0x00, outptr);
    }
}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

After I modified copy.c to update the BITMAPFILEHEADER and BITMAPINFOHEADER of the output of the program, I get a file output, but I cannot open it because of the error, "Invalid or Unsupported Image Format". When I remove the modifications I made below, the file opens. Thanks in advance for helping.

Answer 1

Your calculation for bi.biSizeImage is wrong. The number of bytes per line is bi.biWidth * sizeof(RGBTRIPLE) + outputPadding, and there are abs(bi.biHeight) lines.