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I'm taking the XED course "CS50" and now i'm stuck at pset4.

So far i have managed to resize the images footprint and managed to resize one of the given images by a factor of 2 and 4, but with a factor of 3 it does not work. and i have yet to get the padding to work on images that need that. Here are some of the images of the results of the program

Under are my 2 source codes. Have written one using the recopy method and one using the rewrite method. but got the same problem in both programs.

Recopy method:

    /*
    "recopy"-method
    CS50 2017 pset4 - resize less
    */

    #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;
        }

        if (atoi(argv[1] < 0 || 100 < atoi(argv[1]))
        {
            fprintf(stderr, 
            "Please let the resize facor be between 0 and 100.\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;
        }

        int n = atoi(argv[1]);

        // 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;
        }

        //gives new width
        bi.biWidth *= n;

        //gives new height
        bi.biHeight *= n;

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

        //gives new image size
        bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + padding) 
                            * abs(bi.biHeight);

        //gives new file size
        bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) + 
                    sizeof(BITMAPINFOHEADER);

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

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

        //Offset to move cursor in input file for reading. fseek(); 
        long offset = bi.biWidth * sizeof(RGBTRIPLE) + padding;

        // iterate over infile's scanlines
        for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
        {
            //iterate to print n-lines
            for (int m = 0; m < n;m++ )
            {
                // 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 k = 0; k < n; k++)
                    {
                        // write RGB triple to outfile
                        fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                    }
                }
                //move cursor back to start of line as long as it is not the 
                //last run of writing the line.
                if (m != n - 1)
                {   
                    //Moves the cursor "-offset" bytes back in the input 
                    //file to read from the beginning of the line.
                    fseek(inptr, -offset, SEEK_CUR);
                }
            }
            // skip over padding, if any
            fseek(inptr, padding, SEEK_CUR);

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

        // close infile
        fclose(inptr);

        // close outfile
        fclose(outptr);

        // success
        return 0;
    }

Then the rewrite method:

    /*
    "rewrite" method
    CS50 2017 pset4 - resize less
    */

    #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;
        }

        if (atoi(argv[1] < 0 || 100 < atoi(argv[1]))
        {
            fprintf(stderr, "Please let the resize facor be 
            between 0 and 100.\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;
        }

        int n = atoi(argv[1]);

        // 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;
        }

        //gives new width
        bi.biWidth *= n;

        //gives new height
        bi.biHeight *= n;

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

        //gives new image size
        bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + padding) 
                            * abs(bi.biHeight);

        //gives new file size
        bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) 
                    + sizeof(BITMAPINFOHEADER);

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

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

        //Initiates an array of triples with size bi.biwidth 
            * sizeof(RGBTRIPLE) bytes.
        RGBTRIPLE array[bi.biWidth * sizeof(RGBTRIPLE)];

        // iterate over infile's scanlines
        for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; 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);
                    //Saves each pixel (3 bytes) in an array.
                    array[j] = triple;
                }
                //Iterate over how many lines to write
                for (int l = 0; l < n; l++)
                {
                    //Iterate over line to write the pixels
                    for (int m = 0; m < bi.biWidth; m++)
                    {
                        //write every pixel g times.
                        for (int g = 0; g < n; g++)
                        {
                         fwrite(&array[m], 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 < padding; k++)
            {
                fputc(0x00, outptr);
            }
        }

        // close infile
        fclose(inptr);

        // close outfile
        fclose(outptr);

        // success
        return 0;
    }

A lot(!) of code, i know, that's why i'm so frustrated when i got 2 methods working the same way with the same faults... I can provide the pictures in question if needed but the code should work on all 24-bit uncompressed BMP 4.0 images. resizing a 12*12px by a factor of 2 and 4 is OK, but 3 fails... Also an 3*3px image fails any factors and the smiley face of 8*8px also fails. Thank you in advance!

1

Note that the padding of input and output file might be different, so use two variables for those. Also, an input line does contain a different number of pixels than an output line, you might want to use input file dimensions instead of output file dimensions in some places.

1
  • Awesome answer dude! Just what i needed without it being to obvious so i had to think and draw it out. Thank you so much!
    – Chris
    May 16 '17 at 3:25

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