resize.c

/**
 * copy.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * Resizes a bmp image by a factor n.
 */

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

#include "bmp.h"

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

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

    // remembers factor to resize
    int n = atoi(argv[1]);
    if (n <= 0 || n > 100)
    {
        printf("n must be a positive integer less than or equal to 100\n");
        return 2;
    }

    // open input file
    FILE* inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        printf("Could not open %s.\n", infile);
        return 3;
    }

    // open output file
    FILE* outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 4;
    }

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

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

    // ensure infile is (likely) a 24-bit uncompressed BMP 4.0
    if (bfold.bfType != 0x4d42 || bfold.bfOffBits != 54 || biold.biSize != 40 ||
        biold.biBitCount != 24 || biold.biCompression != 0)
    {
        fclose(outptr);
        fclose(inptr);
        fprintf(stderr, "Unsupported file format.\n");
        return 5;
    }

    // creates new headers
    BITMAPFILEHEADER bfnew = bfold;
    BITMAPINFOHEADER binew = biold;

    // calculates resized dimensions
    binew.biWidth = biold.biWidth * n;
    binew.biHeight = biold.biHeight * n;

    // determines the padding of infile
    int padding_old =  (4 - (biold.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // determines padding for the new image
    int padding_new = (4 - (binew.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // updates headers for the outfile
    binew.biSizeImage = (binew.biWidth + padding_new) * abs(binew.Height);
    bfnew.bfSize = 54 + binew.biSizeImage;

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

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

    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        for (int a = 0; a < n; a++)
        {
            // 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 l = 0; l < n; l++)
                {
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                }
            }

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

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

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // that's all folks
    return 0;
}