Enlarging bitmap in c - c

Question

The following code takes in a bmp and enlarges it, rotates it or flips it. Everything is working properly except when i call the enlarge command line. the pictures comes up but it does not look any bigger.
This is the enlarge funtions:
int enlarge(PIXEL* original, int rows, int cols, int scale,
PIXEL** new, int* newrows, int* newcols)
{
int row, col, i, j;
if((rows<=0)|| (cols<=0))
{
return -1;
}
*newrows=rows * scale;
*newcols=cols * scale;
*new=(PIXEL*)malloc((scale*rows)*(scale*cols)*sizeof(PIXEL));
for(row=0;row<rows;row++)
{
for(col=0;col<cols;col++)
{
PIXEL *o=original + row*cols +col;
for(j=0; j<scale;j++)
{
for(i=0; i<scale;i++)
{
PIXEL *n=(*new)+(row*scale+i)*(*newcols)+(col*scale+j);
*n=*o;
}
}
}
}
/* THIS IS THE METHOD THAT YOU SHOULD WRITE */
return 0;
}
and this is the main function:
int degree, scale;
int is_rotate=0, is_scale=0, is_flip=0;
char *inputFile=NULL, *outputFile=NULL;
int r, c, check;
PIXEL *b, *nb;
int nr,nc;
int error;
//readFile("example.bmp",&r,&c,&b);
while((check=getopt(argc,argv,"s:r:o:f")) != -1)
{
switch (check)
{
case 's':
is_scale=is_scale+1;
//enlarge(nb,nr,nc,optarg,&nb,&nr,&nc);
scale=atoi(optarg);
if(is_scale==2)
{
printf("bmptool: -s: scale can only be called once in commmand line");
error=1;
}
if(scale<0)
{
printf("bmptool: -s : the scale must be a positive integer");
error=1;
}
//printf("This is working s");
break;
case 'r':
is_rotate= is_rotate+1;
//rotate(b,r,c,optarg,&b,&r,&c);
degree=atoi(optarg);
if(is_rotate==2)
{
printf("bmptool: -r: rotation can only be called once in commmand line");
error=1;
}
if(degree%90 != 0)
{
printf("bmptool: -r: the degree of rotation must be a multiple of 90");
error=1;
}
//printf("this is working r");
break;
case 'f':
is_flip=is_flip+1;
if(is_flip==2)
{
printf("bmptool: -f: flip can only be called once in command line");
}
break;
case 'o':
outputFile=(optarg);
//printf(outputFile);
//readFile(outputFile,&r,&c,&b);
break;
}
}
if(error==1)
{
return 0;
}
if(is_rotate==0 && is_scale==1 && is_flip==0)
{
enlarge(nb,nr,nc,scale,&nb,&nr,&nc);
writeFile(inputFile,r,c,b);
}
I only added the if statement that contains the enlarge. Thanks in advance for the help.

Answer 1

Try this:
int enlarge(PIXEL* original, int rows, int cols, float scale,
PIXEL** enlarged, int* newrows, int* newcols)
{
int row, col;
if((rows<=0)|| (cols<=0))
{
return -1;
}
(*newrows)=(int)((float)rows * scale);
(*newcols)=(int)((float)cols * scale);
*enlarged=(PIXEL*)malloc((*newrows)*(*newcols)*sizeof(PIXEL));
for(row=0;row<(*newrows);row++)
{
for(col=0;col<(*newcols);col++)
{
(*enlarged)[row * (*newcols) + col] = original[(row * rows / (*newrows)) * cols + col * cols / (*newcols)];
}
}
/* THIS IS THE METHOD THAT YOU SHOULD WRITE */
return 0;
}
NOTE: i change scale type to float in order to you could scale in any factor, but you could change to int with any problem
You must pass newrows and newcols by ref (not pointer)
EDIT: function usage
scale = 2.0f;
readFile("example.bmp",&r,&c,&b);
enlarge(b,r,c,scale,&nb,&nr,&nc);
writeFile("enlarge.bmp",nr,nc,nb);
free(nb);

Answer 2

If this is a standard Windows bitmap, then newrows must be of a scanline size. A bitmap image consists of scanlines. A scanline consists of pixels. A pixel consists of one or more components (colors).
A scanline must be a multiple of 4 bytes. So after the last component of the last pixel of a scanline, there may follow some unused bytes.
So your scaled bitmap must have scanlines of the appropriate size. See also
Dealing with padding in a BMP file in C of how to calculate scanline sizes and iterate over an image.
Note also that if you just "scale" with an integer, you can scale 1, 2, 3... integer times (100%, 200%,...). Scaling with non-integers requires smearing the pixels out over the new width and hight. Numerous algorithms and ready-to-use code are available on the internet.