CS50 resize "Invalid or Unsupported Image Format" in the IDE

Question

I know that this question has been "answered" numerous times but those revelations haven't related to me for some reason. My code is edited from copy.c and a few other resources. The FILE reads and writes before INFO headers in both instances. I ran debug50 on my code and then someone elses that I copied into a different file but same results happen each time. I tried it with a third and same thing. The only thing I saw that was weird was that it skipped completely over the scanLine for loop and I think it's because bi.biHeight is -3 throughout the whole process. I don't know if that's supposed to be a negative or if it even matters but nothing is happening within that for loop I'm sure. I did the math manually and it makes sense. the xxd terminal output is fudged. Please, please, please, help even though this has been answered. I'm not finding success through those answers.

/**
 * Resizes a BMP piece by piece
 */

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

#include "bmp.h"

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

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

    int multiplier = atoi(argv[1]);
    printf("multiplier: %d\n", multiplier);

    //end program if multiplier is negative or too large
    if(multiplier < 1 || multiplier > 100)
    {
        printf("Invalid zoom factor of %i\n Zoom factor must be 1-100\n", multiplier);
        return 5;
    }

    // open input file 
    FILE *small = fopen(infile, "r");

    if (small == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", "small");
        return 2;
    }

    // open output file
    FILE *zoom = fopen(outfile, "w");
    if (zoom == NULL)
    {
        fclose(small);
        fprintf(stderr, "Could not create %s.\n", "zoom");
        return 3;
    }

    // read infile's BITMAPFILEHEADER
    BITMAPFILEHEADER bf;
    fread(&bf, sizeof(BITMAPFILEHEADER), 1, small);

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

    // 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(zoom);
        fclose(small);
        fprintf(stderr, "Unsupported file format.\n");
        return 4;
    }

        BITMAPFILEHEADER bfOut;
        BITMAPINFOHEADER biOut; 
        bfOut = bf;
        biOut = bi;
        biOut.biWidth = bi.biWidth * multiplier;
        biOut.biHeight = bi.biHeight * multiplier;

        int paddingIn =  (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
        int paddingOut =  (4 - (biOut.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

        bfOut.bfSize = 54 + biOut.biWidth * abs(biOut.biHeight) * 3 + abs(biOut.biHeight) *  paddingOut;
        biOut.biSizeImage = ((((biOut.biWidth * biOut.biBitCount) + 31) & ~31) / 8) * abs(biOut.biHeight);


    // //multiply image size
    // biOut.biWidth = bi.biWidth * multiplier;
    // biOut.biHeight = bi.biHeight * multiplier;
    // printf("biWidth:  %d\n", biOut.biWidth);
    // printf("biHeight: %d\n", biOut.biHeight);

    // //determine padding for scanlines
    // int paddingIn = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    // int paddingOut = (4 - (biOut.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    // printf("paddingIn: %d | width: %d\n", paddingIn, bi.biWidth);
    // printf("paddingOut: %d\n", paddingOut);

    // determine file size
    // biOut.biSizeImage = ((biOut.biWidth * sizeof(RGBTRIPLE)) + paddingOut) * biOut.biHeight;
    // bfOut.bfSize = bf.bfSize - bi.biSizeImage + biOut.biSizeImage;

    // write outfile's BITMAPFILEHEADER
    fwrite(&bfOut, sizeof(BITMAPFILEHEADER), 1, zoom);

    // write outfile's BITMAPINFOHEADER
    fwrite(&biOut, sizeof(BITMAPINFOHEADER), 1, zoom);

    // iterate over height of file
    for (int i = 0; i < (bi.biHeight = abs(bi.biHeight)); i++)
    {
        // iterate over infile's scanlines
        for (int scanLine = 0; scanLine < multiplier; scanLine++) 
        {
            // 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, small);

                // write RGB triple to outfile
                for (int w = 0; w < multiplier; w++)
                {
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, zoom);
                }
            }
            // skip over padding, if any
            fseek(small, paddingIn, SEEK_CUR);

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

                fseek(small, -(bi.biWidth * 3 + paddingIn), SEEK_CUR);
        }

        fseek(small, bi.biWidth * 3 + paddingIn, SEEK_CUR);




        // if(i % multiplier != 0)
        // {
        //     fseek(small, (-biOut.biWidth * /*sizeof(RGBTRIPLE)*/3) + paddingIn, SEEK_CUR);
        // }
    }

    // close infile
    fclose(small);

    // close outfile
    fclose(zoom);

    // success
    return 0;
}

Answer 1

There is a single significant issue that is affecting the code in several places. It appears that you were starting to comprehend it, so let's fill in the blank.

Yes, the sign of biHeight is significant. It determines whether the image is painted on the screen from the top down or from the bottom up as the data is sequentially read. The sign of biHeight must be preserved when the image file is processed.

However, the absolute value of biHeight is used for several functions in this pset and must be positive for these purposes, no matter whether the sign of biHeight is positive or negative. You need to deal with this in your code.

The code will need a few mods to function correctly. Once completed, there are other issues that also need to be identified and corrected, but who am I to deprive you of that opportunity? ;-)

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

Answer 2

I found several finished products online and cross-referenced them to mine and found 2 significant reasons why my code was off. First, and most apparent was the fseek usage. I honestly don't see how the computation is incorrect while using the sizeof(RGBTRIPLE) but replacing that with 3 worked in this case. Second, the equation I was using to change the file size was way off. I found a crazy one and popped that in and voila! The little "black box" works with my code.  

I left the broken parts there and commented them out. I edited how I declared the biOut and bfOut. AND I changed the for loops to include fseek BEFORE the exit of the scanLine loop...phew