Add margin option to trim operation #4480

lib/resize.js

@@ -540,10 +540,19 @@ function extract (options) {
  *   })
  *   .toBuffer();
  *
+ * @example
+ * // Trim image leaving (up to) a 10 pixel margin around the trimmed content.
+ * const output = await sharp(input)
+ *   .trim({
+ *     margin: 10
+ *   })
+ *   .toBuffer();
+ *
  * @param {Object} [options]
  * @param {string|Object} [options.background='top-left pixel'] - Background colour, parsed by the [color](https://www.npmjs.org/package/color) module, defaults to that of the top-left pixel.
  * @param {number} [options.threshold=10] - Allowed difference from the above colour, a positive number.
  * @param {boolean} [options.lineArt=false] - Does the input more closely resemble line art (e.g. vector) rather than being photographic?
+ * @param {number} [options.margin=0] - Leave a margin around trimmed content, value is in pixels.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
  */
@@ -564,6 +573,13 @@ function trim (options) {
       if (is.defined(options.lineArt)) {
         this._setBooleanOption('trimLineArt', options.lineArt);
       }
+      if (is.defined(options.margin)) {
+        if (is.integer(options.margin) && options.margin >= 0) {
+          this.options.trimMargin = options.margin;
+        } else {
+          throw is.invalidParameterError('margin', 'positive integer', options.margin);
+        }
+      }
     } else {
       throw is.invalidParameterError('trim', 'object', options);
     }