I'm able to resize a given *.bmp* horizontally, but the code for vertical resizing is not working. Here is my code for vertical expansion.
// resize vertically
//move pointer to start of scanline of outptr
fseek(outptr, -3 * (bi2.biWidth + padding), SEEK_CUR);
fgetpos (outptr,&pos);
//an array of RGBTRIPLE to store one scanline
RGBTRIPLE triple[bi2.biWidth + padding];
//reading the already written first line
for (int p = 0 ; p < bi2.biWidth + padding; p++)
{
fread(&triple[p], sizeof(RGBTRIPLE), 1, outptr);
}
fgetpos (outptr,&pos);
//writing the copied array to outptr
for (int k = 0 ; k < n; k++)
{
for (int p = 0 ; p < bi2.biWidth + padding; p++)
fwrite(&triple[p], sizeof(RGBTRIPLE), 1, outptr);
}
This is executed after reading the first scanline of the original *bmp*. I used *gdb* to see the values of `triple`'s elements, but I found that they're all garbage values.
Also when I check the position of the file position indicator in `outptr` using `fgetpos()`, I find it not changing!
----------
**Update:** here's my code after modifications
// iterate over infile's scanlines
fpos_t pos;
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
// iterate over pixels in scanline
fgetpos (outptr,&pos);
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 n times horizontally
for (int k = 0 ; k < n; k++)
{
fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
}
}
// skip over padding in infile, if any
fseek(inptr, padding_in, SEEK_CUR);
// then add padding to outfile
for (int l = 0; l < padding; l++)
{
fputc(0x00, outptr);
}
// resize vertically
//move pointer to start of scanline of outptr
fsetpos( outptr, &pos );
//an array of RGBTRIPLE to store one scanline
RGBTRIPLE triplex[bi2.biWidth];
//reading the already written first line
for (int m = 0 ; m < bi2.biWidth ; m++)
{
fread(&triplex[m], sizeof(RGBTRIPLE), 1 , outptr);
}
//skip padding
fseek(outptr, padding, SEEK_CUR);
for (int mn = 0 ; mn < n ; mn++)
{
//writing the copied array to outptr
for (int o = 0 ; o < bi2.biWidth ; o++)
{
fwrite(&triplex[o], sizeof(RGBTRIPLE), 1 , outptr);
}
for (int p = 0; p < padding; p++)
{
fputc(0x00, outptr);
}
}
}
complete program
/**
* copy.c
*
* Computer Science 50
* Problem Set 5
*
* Copies a BMP piece by piece, just because.
*/
#include <stdio.h>
#include <stdlib.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>//for isdigit
#include "bmp.h"
int main(int argc, char* argv[])
{
// ensure proper usage
if (argc != 4)
{
printf("Usage: ./resize n infile outfile\n");
return 1;
}
//checking if n is integer
int i=0;
string in=argv[1];
while(in[i]!='\0')
{
if( isdigit(in[i]) )
i++;
else
{
printf("n, the resize factor, must be an integer.\n");
return 5;
}
}
int n=atoi(in);
if(n<1 || n>100)
{
printf("n, the resize factor, must be a positive integer less than 100.\n");
return 6;
}
// remember filenames
char* infile = argv[2];
char* outfile = argv[3];
// 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;
}
// outfile's BITMAPFILEHEADER
BITMAPFILEHEADER bf2=bf;
// outfile's BITMAPINFOHEADER
BITMAPINFOHEADER bi2=bi;
//multiplying width by n factor
bi2.biWidth = n*(bi.biWidth);
//multiplying height by n factor
bi2.biHeight = n*(bi.biHeight);
// determine padding for scanlines in outfile
int padding = (4 - (bi2.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
// determine padding for scanlines in infile
int padding_in = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
//size of the image
bi2.biSizeImage = (bi2.biWidth + padding) * (abs(bi2.biHeight)) * 3;// positive bi2.biHeight for calculation of bi2.biSizeImage
//final size of bmp
bf2.bfSize = bi2.biSizeImage + 54;
// write outfile's BITMAPFILEHEADER
fwrite(&bf2, sizeof(BITMAPFILEHEADER), 1, outptr);
// write outfile's BITMAPINFOHEADER
fwrite(&bi2, sizeof(BITMAPINFOHEADER), 1, outptr);
// iterate over infile's scanlines
fpos_t pos;
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
// iterate over pixels in scanline
fgetpos (outptr,&pos);
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 n times horizontally
for (int k = 0 ; k < n; k++)
{
fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
}
}
// skip over padding in infile, if any
fseek(inptr, padding_in, SEEK_CUR);//padding_in is padding in inptr
// then add padding to outfile
for (int l = 0; l < padding; l++)//padding is padding in outptr
{
fputc(0x00, outptr);
}
//flushing the buffer to outptr
fflush(outptr);
// resize vertically
//move pointer to start of scanline of outptr
fsetpos( outptr, &pos );
//an array of RGBTRIPLE to store one scanline
RGBTRIPLE triplex[bi2.biWidth];
//reading the already written first line from outptr
for (int m = 0 ; m < bi2.biWidth ; m++)
{
fread(&triplex[m], sizeof(RGBTRIPLE), 1 , outptr);
}
//skip padding
fseek(outptr, padding, SEEK_CUR);
//writing the values in array to outptr n times
for (int mn = 0 ; mn < n ; mn++)
{
//writing values from the array
for (int o = 0 ; o < bi2.biWidth ; o++)
{
fwrite(&triplex[o], sizeof(RGBTRIPLE), 1 , outptr);
}
//adding padding to outptr's scanline
for (int p = 0; p < padding; p++)
{
fputc(0x00, outptr);
}
}
}
// close infile
fclose(inptr);
// close outfile
fclose(outptr);
// that's all folks
return 0;
}