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Author: sm7515

src/data/examples/assets/frontier.jpg

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+/*
+ * @name Histogram
+ * @description Calculates the histogram of an image. 
+ * A histogram is the frequency distribution of the gray levels with the number of 
+ * pure black values displayed on the left and number of pure white values on the right. 
+ * Note that this sketch will behave differently on Android, since most images will 
+ * no longer be full 24-bit color.
+ */
+
+let img;
+let hist = [];
+
+function preload() {
+  // Load an image from the data directory
+  // Load a different image by modifying the comments
+  img = loadImage('assets/frontier.jpg');
+}
+
+function setup() {
+  createCanvas(640, 360);
+  image(img, 0, 0);
+
+  // Initialize the histogram
+  for (let i = 0; i < 256; i++) {
+    hist.push(0);
+  }
+
+  // Calculate the histogram
+  for (let i = 0; i < img.width; i++) {
+    for (let j = 0; j < img.height; j++) {
+      let bright = int(brightness(img.get(i, j)));
+      hist[bright]++;
+    }
+  }
+}
+
+function draw(){
+  // Find the largest value in the histogram
+  let histMax = max(hist);
+  stroke(255);
+  // Draw half of the histogram (skip every second value)
+  for (let i = 0; i < img.width; i += 2) {
+    // Map i (from 0..img.width) to a location in the histogram (0..255)
+    let which = int(map(i, 0, img.width, 0, 255));
+    // Convert the histogram value to a location between
+    // the bottom and the top of the picture
+    let y = int(map(hist[which], 0, histMax, img.height, 0));
+    line(i, img.height, i, y);
+  }
+}