Pset4, padding, Resize

Question

I was trying to solve resize problem, I started by resizing horizontally, it worked, but the image is corrupted, because the code messes the padding part, I'm not sure I understand padding and the fseek() part, so a little help would be appreciated. this is the code till now: /** * Copies a BMP piece by piece, just because. */

include

include

include "bmp.h"

int main(int argc, char *argv[]) { int newPadding; int z=0; // ensure proper usage if (argc != 4) { fprintf(stderr, "Usage: ./copy infile outfile\n"); return 1; }

// remember filenames
int n=atoi(argv[1]);
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;

//determine new width & height
bi.biWidth=n*bi.biWidth;
bi.biHeight=n*bi.biHeight;
newPadding =  (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
bi.biSizeImage=((sizeof(RGBTRIPLE)*bi.biWidth)+newPadding)*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(bi.biHeight); i < biHeight; i++)
{


    // iterate over pixels in scanline
    for (int j = 0; j < bi.biWidth; j++)
    {
        // temporary storage
        RGBTRIPLE triple;

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


            // write RGB triple to outfile
        for(z=0;z<n;z++)
        fwrite(&triple, sizeof(RGBTRIPLE), n, outptr); //write to outfile n times


    }

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

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

}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

Answer 1

You redefine bi.biWidth and bi.biHeight as new, outfile ones. However, in your loop you want to iterate over infile ones.