Image flipping incorrectly...Why?

Question

I am trying to flip my image on a Y Axis, and it does flip, but it leaves odd spaces in the middle and on the right side, it wont flip the entire image perfectly, I am limiting the images to 450 by 450 and a P3...Anyone have any ideas, because my algorithm is correct

for(j=0; j < imgur.width/2; j++)
  {
     for(i=0; i < imgur.height; i++)
        {
           temp.red = imgur.image[i][j].red;
           imgur.image[i][j].red = imgur.image[i][imgur.height-j-1].red;
           imgur.image[i][imgur.height-j-1].red = temp.red;

           temp.green = imgur.image[i][j].green;
           imgur.image[i][j].green = imgur.image[i][imgur.height-j-1].green;
           imgur.image[i][imgur.height-j-1].green = temp.green;

           temp.blue = imgur.image[i][j].blue;
           imgur.image[i][j].blue = imgur.image[i][imgur.height-j-1].blue;
           imgur.image[i][imgur.height-j-1].blue = temp.blue;
     }
  }

Here's my algorithm... Before that I am printing out the P3, the comment, the width and height, and the maxColor. I am using two structs to get the data and reading in a file from the terminal... Here's how I'm printing out the data. Anyone have any ideas?

 for(i=imgur.height-1; i >= 0; i--)
  {
     for(j=0; j < imgur.width; j++)
        {
           printf("%i\n", imgur.image[i][j].red);
           printf("%i\n", imgur.image[i][j].green);
           printf("%i\n", imgur.image[i][j].blue);
        }
  }

Answer 1

my symmetric detector is confused by (in the upper part)

for(j=0; j < imgur.width/2; j++) {
  for(i=0; i < imgur.height; i++) {

and (in the lower part)

for(i=imgur.height-1; i >= 0; i--) {
  for(j=0; j < imgur.width; j++) {

Answer 2

You have made a little typo mistake in the flip algorithm: as you flip upside-down, you have to scan all lines entirely and half of the height of the image, not the inverse.

for(j=0; j < imgur.width; j++)
{
  for(i=0; i < imgur.height/2; i++)
  {
     //code of your loop, removed for compactness
  }
}

EDIT In fact, for left-right swapping, you have also inverted the complement of index j. j is along the X-axis, belonging the range 0:width-1, so the complement is width-1-j.

I have coded a version of this algorithm a long time ago, it was like that:

for (i=0; i!=h; i++) {
    for (j=0; j!=w/2; j++) {
        temp = src[i][w-1-j];
        dst[i][w-1-j] = src[i][j];
        dst[i][j] = temp;
    }
}

I think it works fine (As you are working with a pixel struct, it is perfectly correct to swap the whole pixel like this).