Add experimental 'attention' crop strategy

test/saliency/humanae/download.js

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+'use strict';
+/*jshint esversion: 6 */
+
+const fs = require('fs');
+const request = require('request');
+const tumblr = require('tumblr.js');
+
+const client = tumblr.createClient({
+  consumer_key: '***',
+  consumer_secret: '***'
+});
+
+const fetchImages = function(offset) {
+  console.log(`Fetching offset ${offset}`);
+  client.posts('humanae', {
+    type: 'photo',
+    offset: offset
+  }, function (err, response) {
+    if (err) throw err;
+    if (response.posts.length > 0) {
+      response.posts.forEach((post) => {
+        const url = post.photos[0].alt_sizes
+          .filter((image) => image.width === 100)
+          .map((image) => image.url)
+          [0];
+        const filename = `./images/${post.id}.jpg`;
+        try {
+          fs.statSync(filename);
+        } catch (err) {
+          if (err.code === 'ENOENT') {
+            request(url).pipe(fs.createWriteStream(filename));
+          }
+        }
+      });
+      fetchImages(offset + 20);
+    }
+  });
+};
+fetchImages(0);

test/saliency/humanae/package.json

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+{
+  "name": "sharp-crop-strategy-attention-model-humanae",
+  "version": "0.0.1",
+  "private": true,
+  "dependencies": {
+    "request": "^2.75.0",
+    "tumblr.js": "^1.1.1"
+  }
+}

test/saliency/humanae/tone.js

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+'use strict';
+/*jshint esversion: 6 */
+
+const fs = require('fs');
+const child_process = require('child_process');
+
+const a = [];
+const b = [];
+
+fs.readdirSync('./images')
+  .filter((file) => file.endsWith('.jpg'))
+  .forEach((file) => {
+    // Extract one pixel, avoiding first DCT block, and return value of A and B channels
+    const command = `convert ./images/${file}[1x1+8+8] -colorspace lab -format "%[fx:u.g] %[fx:u.b]" info:`;
+    const result = child_process.execSync(command, { encoding: 'utf8' });
+    const ab = result.split(' ');
+    a.push(ab[0]);
+    b.push(ab[1]);
+  });
+
+a.sort((v1, v2) => v1 - v2);
+b.sort((v1, v2) => v1 - v2);
+
+// Convert from 0..1 to -128..128
+const convert = function(v) {
+  return Math.round(256 * (v - 0.5));
+};
+
+const threshold = Math.round(a.length / 100);
+console.log(`Trimming lowest/highest ${threshold} for 98th percentile`);
+
+// Ignore ~2% outliers
+console.log(`a ${convert(a[threshold])} - ${convert(a[a.length - threshold])}`);
+console.log(`b ${convert(b[threshold])} - ${convert(b[b.length - threshold])}`);