I'm stuck on Resize (Less). Please help!

Question

I can't seem to figure out what's wrong with my resize code - it only resizes correctly for n = 1. I've checked the header data when n = 4 compared to large.bmp, and it's the same. If anyone knows what I'm doing wrong, please let me know.

Edit: I've changed my code to make a new bf and bi, and this almost works, but not quite. If you can see the problem here, please help!

// Resizes a bmp file
#include 
#include 
#include "bmp.h"


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

// remember filenames
int n = atoi(argv[1]);
//printf("%i", n);
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, nbf;
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

nbf = bf;

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

nbi = bi;

// 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;
}

// int ogWidth = bi.biWidth;
// int ogHeight = bi.biHeight;
int ogPadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
printf("og Padding: %i\n", ogPadding);

// multiply width and height by n
// this is where the problem is?
nbi.biWidth = bi.biWidth * n;
nbi.biHeight = bi.biHeight * n;

// determine padding for scanlines
int newPadding = (4 - (nbi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4; // Here
printf("new Padding: %i\n", newPadding);

nbi.biSizeImage = ((sizeof(RGBTRIPLE) * nbi.biWidth) + newPadding) * abs(nbi.biHeight); // Here
nbf.bfSize = nbi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

// incorrect because bi.biWidth is still og

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

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

// iterate over infile's scanlines
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{

    for (int o = 0; o < n - 1; o++)
    {
        printf("Yay %i\n", o);
        // iterate over pixels in scanline
        for (int j = 0; j < bi.biWidth; j++) // Here
        {
            // temporary storage
            RGBTRIPLE triple;

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

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

                //printf("in loop %i", p);
            }


        }

        // add padding
        for (int k = 0; k < newPadding; k++)
        {
            fputc(0x00, outptr);
            printf("Padding\n");
        }

        fseek(inptr, -1 * bi.biWidth, SEEK_CUR); // Here

    }

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

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

        // write RGB triple to outfile
        for (int p = 0; p < n; p++){
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            //printf("in loop %i", p);
        }


    }

    // add padding
    for (int k = 0; k < newPadding; k++)
    {
        fputc(0x00, outptr);
        //printf("Padding");
    }

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

    // // Skip back to previous line if necessary
    // int o = (i + 1) % n;
    // printf("o: %i\n", o);

    // if (o > 0)
    // {
    //     int skip = bi.biWidth + ogPadding;
    //     printf("skip: %i\n", skip);
    //     fseek(inptr, -4, SEEK_CUR);
    //     //printf("Gotcha\n");
    // }
}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;


}

Answer 1

You should create a new variable for the width and height of outfile. As you are using the same variable of infile, the compiler may mistakes when adding padding to outfile.