pset4 resize.c Invalid or Unsupported Image Format

Question

I'm working on this code for over two weeks and I still don't know where the problem is. My guess is that I have a problem in the Re-copy method (resizing vertically) or in the padding. I screw up every time I change them. so any help is very appreciated. I'm out of ideas here

/**
 * resize.c
 */

#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
    int factor = atoi(argv[1]);
    char* infile = argv[2];
    char* outfile = argv[3];

     // check available scale/factor number
    if ((factor <= 0) || (factor >= 100))
    {
        printf("valid scale number is between 0 and 100\n");
        return 10 ; 
    }

    // 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 info for outfile  - change these values of the height and width 
    // keeping track of both original and new files
    BITMAPFILEHEADER out_bf;
    BITMAPINFOHEADER out_bi;

    // change file size (bf.size -kolo bl padding) - image size(bi.imagesize) - width(biwidth - padding) - height(biheight)
    out_bi.biWidth = bi.biWidth * factor ; 
    out_bi.biHeight = bi.biHeight * factor ;

    // padding difference formulas
    int padding =  (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int out_padding =  (4 - (out_bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // continue adjusting header files 
    out_bi.biSizeImage = (out_bi.biWidth * sizeof(RGBTRIPLE) + out_padding) * abs(out_bi.biHeight) ; 
    out_bf.bfSize = out_bi.biSizeImage + 54 ;    // 54 = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER)

    // write outfile's headers
    fwrite(&out_bf, sizeof(BITMAPFILEHEADER), 1, outptr);
    fwrite(&out_bi, sizeof(BITMAPINFOHEADER), 1, outptr);

    // iterate over infile's scanlines - iterate over infile's scanlines (rows
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        // every row needs to be copied (n) times = factor 
        for (int v = 0 ; v < factor ; v++)
        {
            // iterate over pixels in scanline
            for (int j = 0; j < bi.biWidth; j++)
            {
                RGBTRIPLE triple;
                fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

                // resize it horizontally 
                for (int h = 0 ; h < factor ; h++)
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }

            // skip padding
            fseek(inptr, padding, SEEK_CUR);

            // add it back  
            for (int k = 0; k < out_padding; k++)
            {
                fputc(0x00, outptr);
            }

            // Re-copy method 
            fseek(inptr, -(out_bi.biWidth * sizeof(RGBTRIPLE) + out_padding), SEEK_CUR);
        }
    }

    fclose(inptr);
    fclose(outptr);
    return 0;
}

Answer 1

There are a couple of issues to deal with. The out_bi and out_bf headers are not being initialized, so except for the fields that are changed, all of the other fields contain garbage data.

Next, the // Re-copy method code is flawed. It uses vars that are intended to be used with the output file to control the file pointer movement for the input file. It is also being executed on every loop. It should not execute after the current line has been processed enough times.

This should get you going. There may be more issues, but that will be for a new question.

If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)