need resize help

Question

i am quite stuck with the vertical procedures on this problem. I've implemented a for loop which will re-draw the horizontal scanline N times, can't figure out why my image is writing black pixels though. Can someone please point me in the right direction?

/**
 * copy.c
 *
 * Computer Science 50
* Problem Set 4
 *
* Copies a BMP piece by piece, just because.
*/

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

#include "bmp.h"

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

// remember filenames
char* infile = argv[2];
char* outfile = argv[3];
int n = atoi(argv[1]);
// tests n
if (n < 1 || n > 100)
    {

        printf("n must between 1 and 100\n");
        return 1;
    }

// open input file 
FILE* inptr = fopen(infile, "r");
if (inptr == NULL)
{
    printf("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;
}

// update header
BITMAPFILEHEADER new_bf = bf;   
BITMAPINFOHEADER new_bi = bi;     

new_bi.biHeight  = bi.biHeight * n;
new_bi.biWidth = bi.biWidth * n;

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

new_bi.biSizeImage = (new_bi.biWidth * sizeof(RGBTRIPLE) + new_padding) * abs(new_bi.biHeight);
new_bf.bfSize = 54 + new_bi.biSizeImage;



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

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


// iterate over infile's scanlines
for (int i = 0, biHeight = abs(new_bi.biHeight); i < biHeight; i++)
{
   // Perform the horizontal resize many times to get a vertical one.
    for (int h = 0; h < n; h++)
    {

    // 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 (int t = 0; t < n; t++)
        {
        fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
        }


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

    }

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

}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// that's all folks
return 0;
[![enter image description here][1]][1]}

Answer 1

What's left for you to do is basically this:

Watch this video:

https://www.youtube.com/watch?v=zOylgRdzv_U&feature=youtu.be&t=10m1s

PS: Other than that, you're iterating over the new height when you should be iterating over the old one.