I was trying to implement the rewrite method. the code compiles without error but I always get a weird result bitmap.
Here is the code I wrote:
#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];
// remember scaling factor
int n = atoi(argv[1]);
//ensure the scaling factor is within the limits
if (n < 1 || n > 100)
{
fprintf(stderr, "n must be a positive integer less than or equal to 100\n");
return 2;
}
// open input file
FILE *inptr = fopen(infile, "r");
if (inptr == NULL)
{
fprintf(stderr, "Could not open %s.\n", infile);
return 3;
}
// open output file
FILE *outptr = fopen(outfile, "w");
if (outptr == NULL)
{
fclose(inptr);
fprintf(stderr, "Could not create %s.\n", outfile);
return 4;
}
// 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 5;
}
// remember the width and height of the infile as well as its padding
int width_in = bi.biWidth;
int height_in = bi.biHeight;
int padding_in = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
//changing the header properties to match the scaling
bi.biWidth *= n;
bi.biHeight *= n;
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
bi.biSizeImage = ((3 * bi.biWidth) + padding) * abs(bi.biHeight);
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);
// iterate over infile's scanlines
for (int i = 0; i < height_in; i++)
{
// declare an array for storing the entire row to be written
RGBTRIPLE row[bi.biWidth];
// iterate over pixels in scanline
for (int j = 0; j < width_in; j++)
{
// temporary storage
RGBTRIPLE triple;
// read RGB triple from infile
fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
// writting the pixel n times in the array
for (int x = 0; x < n; x++)
{
row[x + (n * j)] = triple;
}
}
for (int j = 0; j < n; j++)
{
fwrite(row, sizeof(row), 1, outptr);
for (int k = 0; k < padding; k++)
{
fputc(0x00, outptr);
}
}
// skip over padding, if any
fseek(inptr, padding_in, SEEK_CUR);
}
// close infile
fclose(inptr);
// close outfile
fclose(outptr);
// success
return 0;
}