I31 Answer ― Histogram

#include <stdlib.h>
#include <stdio.h>
#include "../basicImage.c"

void statistics( image img, double *avg, double *sd )
{
  int r, c, value ;
  double sum = 0.0;
  double sumOfSquares = 0.0;
  double avgSumOfSquares = 0.0;

  for ( r=0; r<img.nrows; r++ )
    for ( c=0; c<img.ncols; c++ )
    {
      value = getPixel( img, r, c ) ;
      sum += value;
      sumOfSquares += value*value;
    }
    
  *avg = sum/(img.nrows*img.ncols);
  avgSumOfSquares = sumOfSquares/(img.nrows*img.ncols);
  *sd = sqrt( avgSumOfSquares - *avg * *avg );
}

void histogram ( image img, int histo[] )
{
  int r, c, j, value;
  
  for ( j=0; j<255; j++ ) histo[j] = 0;
  
  for ( r=0; r<img.nrows; r++ )
    for ( c=0; c<img.ncols; c++ )
    {
      value = getPixel( img, r, c ) ;
      histo[value]++ ;
    }
}

void displayHist( int histo[] )
{
  const int maxStars = 15; /* number of stars maximum in a column */
  const int displayWidth = 64;
  int compHisto[displayWidth];
  
  int pixPerStar;
  int gray;
  int r, c, j, line, max;

  /* compress the histogram for a compact display */
  for ( j=0; j<displayWidth; j++ )
    compHisto[j] = histo[j*4]+histo[j*4+1]+histo[j*4+2]+histo[j*4+3];

  /* Scan for maximum value in compressed histogram */
  max = compHisto[0];
  for ( j=0; j<displayWidth; j++ )
    if ( compHisto[j] > max ) max = compHisto[j];

  /* How many pixels per star? */
  pixPerStar = max/maxStars;

  /* Print the Histogram */
  for ( line=maxStars; line>0; line-- )
  {
    printf("| ");
    for ( gray=0; gray<displayWidth ; gray++ )
      if ( compHisto[gray] >= pixPerStar*line ) printf("*");
      else printf(" ");
    printf("\n");
  }
  
  /* Print the Horizontal Axis */
  printf("-");
  printf("-");
  for ( gray=0; gray<displayWidth; gray++ ) printf("-");
  printf("\n");
}

int main ( int argc, char* argv[] )
{
  image  img;
  double average, stdDev ;
  int hist[256] = { 0 };
  
  if ( argc != 2 )
  {
    printf("histogram imageFile\n");
    exit( EXIT_FAILURE );
  }
  
  /* read in the image */
  readPGMimage( &img, argv[1]);
  
  /* compute statistics and histogram */
  statistics( img, &average, &stdDev ) ;
  histogram ( img, hist );

  /* display the results */
  displayHist( hist );
  printf("average: %lf\tstandard deviation: %lf\n", average, stdDev) ;
    
  /* free memory */
  freeImage( &img );
}

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