Pset4 Resize (less) vertically re-copy not working - no idea why, help badly needed

Question

/** * Copies a BMP piece by piece, just because. */

include

include

include "bmp.h"

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

//ensure proper n
int n = atoi(argv[1]);
if (n<=0 || n>100)
{
    fprintf(stderr, "Incorrect multiplication factor\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;

//****define new headers
BITMAPFILEHEADER new_bf = bf;
BITMAPINFOHEADER new_bi = bi;

//****define new header variables
new_bi.biWidth = bi.biWidth *=n;
new_bi.biHeight = bi.biHeight *=n;

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

//****define new header variables
new_bi.biSizeImage = ((sizeof(RGBTRIPLE) * new_bi.biWidth)+new_padding)*abs(new_bi.biHeight);
new_bf.bfSize = new_bi.biSizeImage +sizeof(BITMAPFILEHEADER)+ sizeof(BITMAPINFOHEADER);

// 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(bi.biHeight); i < biHeight; i++)
{
// repeat the scanline
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);

        for (int g = 0; g < n; g++)
        {
        // write RGB triple to outfile n times
        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 < new_padding; k++)
    {
        fputc(0x00, outptr);
    }
if (h!=(n-1))
fseek(inptr, -(bi.biWidth *sizeof(RGBTRIPLE)+padding), SEEK_CUR);
}
}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

Answer 1

The outermost for loop needs to use the input height, not output height. Same applies for the width later.

Replace

    //****define new header variables
    new_bi.biWidth = bi.biWidth *=n;
    new_bi.biHeight = bi.biHeight *=n;

with

    //****define new header variables
    new_bi.biWidth = bi.biWidth * n;
    new_bi.biHeight = bi.biHeight * n;