// Histogram 
// By REAS <http://reas.com> 

size(200, 200); 
colorMode(RGB, width); 
 
int[] hist = new int[width]; 
 
// Load an image from the data directory 
// Load a different image by modifying the comments 
PImage a; 
a = loadImage("cdi01_g.jpg"); 
image(a, 0, 0); 
 
// Calculate the histogram 
for (int i=0; i<width; i++) { 
  for (int j=0; j<height; j++) { 
    hist[int(red(get(i, j)))]++; 
  } 
} 
 
// Find the largest value in the histogram 
float maxval = 0; 
for (int i=0; i<width; i++) { 
  if(hist[i] > maxval) { 
    maxval = hist[i]; 
  }  
} 
 
// Normalize the histogram to values between 0 and "height" 
for (int i=0; i<width; i++) { 
  hist[i] = int(hist[i]/maxval * height); 
} 
 
// Draw half of the histogram (skip every second value) 
stroke(width); 
for (int i=0; i<width; i+=2) { 
  line(i, height, i, height-hist[i]); 
}