Why is my image from my ppm file a little off?

Question

The task is to create an image of the russian flag on an image with 800 columns and 600 rows. So, the flag is divided into three equal sections (white on top, blue in the middle, and red on the bottom)

Here's my code:

#include <stdio.h>

int main() {
   printf("P6\n");
   printf("%d %d\n", 800, 600);
   printf("255\n");

   int width, heightWhite, heightBlue, heightRed, i, j;
   unsigned char Rcolor, Bcolor, Gcolor;

   width = 800;
   heightWhite = 200;
   heightBlue = 400;
   heightRed = 600;

   for (j = 0; j <= heightWhite; j++) {
      for (i = 0; i <= width; i++) {
         Rcolor = 255;
         Bcolor = 255;
         Gcolor = 255;

         printf("%c%c%c", Rcolor, Gcolor, Bcolor);
      }
   }

   for (j = 201; j <= heightBlue; j++) {
      for (i = 0; i <= width; i++) {
         Rcolor = 0;
         Bcolor = 255;
         Gcolor = 0;

         printf("%c%c%c", Rcolor, Gcolor, Bcolor);
      }
   }

   for (j = 401; j <= heightRed; j++) {
      for (i = 0; i <= width; i++) {
         Rcolor = 255;
         Bcolor = 0;
         Gcolor = 0;

         printf("%c%c%c", Rcolor, Gcolor, Bcolor);
      }
   }

   return (0);
}

But when I looked at the image generated by my program, I noticed that the top of the blue and red bars aren't completely horizontal (it looks like part of the row that makes the top of the blue and red bar are higher up than the preceding pixels) I can't figure out why I'm getting this. I already ran my instructor's ppm file on Gimp (which is what I use to view ppm files) and the lines ARE supposed to be perfectly level. Any ideas?

(I'm not sure how to attach my ppm file, but here's what it's supposed to look like: http://users.csc.calpoly.edu/~dekhtyar/101-Fall2013/labs/lab7.html) (It's the very first flag)

David Ranieri · Accepted Answer · 2013-10-29T07:58:10.823

0

You are printing one more pixel for each row (the last row of each color prints 200 pixels more).

Change

for (i = 0; i <= width; i++) {

to

for (i = 0; i < width; i++) {

EDIT:

but how come I can say "<=" for the height?

for (j = 0; j < heightWhite; j++)  = 0...199 = 200 items
for (j = 1; j <= heightWhite; j++) = 1...200 = 200 items

Note that all your code can be executed with two loops:

#include <stdio.h>

int main(void)
{
   int width = 800, height = 600, icolor = 0, i, j;
   unsigned char color[][3] = {
      {255, 255, 255}, /* white */
      {0, 0, 255},     /* blue */
      {255, 0, 0}      /* red */
   };

   printf("P6\n");
   printf("%d %d\n", width, height);
   printf("255\n");

   for (i = 0; i < height; i++) {
      for (j = 0; j < width; j++) {
         printf("%c%c%c", color[icolor][0], color[icolor][1], color[icolor][2]);
      }
      if (i && (i % 200 == 0)) icolor++; /* 200, 400, 600 */
   }
   return 0;
}

edited Oct 29 '13 at 07:58

answered Oct 29 '13 at 06:37

David Ranieri

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Ahh I see! Just curious, but how come I can say "<=" for the height? Thanks for the help! – Oct 29 '13 at 06:42
I think your modulo trick is a bit too clever. Explicitely respecting the different width with three loop for each color would IMO be simpler to understand, and would work with color patches of different width. – shodanex Oct 29 '13 at 08:08
Well, since all bars have the same height, I see no problem with the use of modulo. – David Ranieri Oct 29 '13 at 08:29
Sorry, the OP posted a similar question with vertical bars – shodanex Oct 29 '13 at 08:35

Why is my image from my ppm file a little off?

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