I managed to make resize work using a static array to store a row of pixels for the outfile (rewrite method). However, my first attempt with a dynamic array doesn't work, and I don't understand why. The size of the array should be the same as the static one (RGBTRIPLE* rowBuff = malloc(sizeof(RGBTRIPLE) * bi.biWidth); //where bi.biWidth is the updated width after multiplying by the resizing factor
). I've tried to make the following code as clear as possible:
// Copies a BMP file and rescales by factor
#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 scalefactor infile outfile\n");
return 1;
}
// remember filenames
int scale = atoi(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 1;
}
// open output file
FILE *outptr = fopen(outfile, "w");
if (outptr == NULL)
{
fclose(inptr);
fprintf(stderr, "Could not create %s.\n", outfile);
return 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 1;
}
//store original height, width and padding of the INFILE
LONG origHeight = bi.biHeight;
LONG origWidth = bi.biWidth;
int origPadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
//printf("%d\t%d\t%d\n", origHeight, origWidth, origPadding);
// Edit headers based on scale factor
bi.biWidth *= scale;
bi.biHeight *= scale;
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
bi.biSizeImage = ((sizeof(RGBTRIPLE) * 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);
// create buffer that has enough space to store one row of pixels for the OUTFILE
RGBTRIPLE* rowBuff = malloc(sizeof(RGBTRIPLE) * bi.biWidth);
//RGBTRIPLE rowBuff[bi.biWidth];
//printf("%lu\t%d\t%lu\t\n", sizeof(RGBTRIPLE), bi.biWidth, sizeof(rowBuff));
// iterate over infile's scanlines
for (int i = 0, biHeight = abs(origHeight); i < biHeight; i++)
{
int curindex = 0;
// iterate over pixels of infile scanline
for (int j = 0; j < origWidth; j++)
{
// temporary storage
RGBTRIPLE triple;
// read RGB triple from infile
fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
// write RGB triple to rowBuff n times
for(int x = 0; x < scale; x++)
rowBuff[curindex++] = triple;
}
curindex = 0;
//for n times, write array to outfile and write outfile padding
for (int x = 0; x < scale; x++)
{
fwrite(rowBuff, sizeof(rowBuff), 1, outptr);
for (int k = 0; k < padding; k++)
{
fputc(0x00, outptr);
}
}
// skip over INFILE padding, if any
fseek(inptr, origPadding, SEEK_CUR);
}
// close infile
fclose(inptr);
// close outfile
fclose(outptr);
free(rowBuff);
// success
return 0;
}
I'm stumped here. I'm done with this problem but I'd like to know why my approach didn't work