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I am back again with another question about resize more. I feel like I am pretty close, but for some reason it is not resizing vertically properly when the factor is larger than 0 (I haven't dabbled in shrinking yet). Here is my code:

// Copies a BMP file

#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 factor infile outfile\n");
        return 1;
    }

    // remember filenames
    float factor = atof(argv[1]);
    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);
    BITMAPINFOHEADER newBi;
    BITMAPFILEHEADER newBf;
    newBf = bf;
    newBi = bi;
    newBi.biWidth = bi.biWidth * factor;
    newBi.biHeight = bi.biHeight * factor;

    // 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;
    int newPadding = (4 - (newBi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    newBi.biSizeImage = ((newBi.biWidth) * sizeof(RGBTRIPLE) + (newPadding)) * abs(newBi.biHeight);
    newBf.bfSize = (bf.bfSize - bi.biSizeImage) + newBi.biSizeImage;

    // Changes image size
    newBi.biSizeImage = (newBi.biHeight * sizeof(RGBTRIPLE) + newPadding) * abs(newBi.biHeight);

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

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

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

            // Writes pixels horizontally
            for (int h = 0; h < factor; h++)
            {
                for (int w = 0; w < factor; w++)
                {
                    // write RGB triple to outfile
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                }
            }
        }

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

        printf("Padding needed: %i vs old padding %i\n", newPadding, padding);
        // then add it back (to demonstrate how)
        for (int k = 0; k < newPadding; k++)
        {
            fputc(0x00, outptr);
        }
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}
1

It looks to me like the code is writing the output padding after factor lines have been written out, not after EACH line.

Say that factor is 3. The code writes out the current line of pixels out 3 times, but only writes out the padding after the 3rd line is finished. It should be writing out the padding at the end of each line.

The code needs a little bit of restructuring to fix this. ;-)

Also, check your headers. There's still a problem there.

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

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