Expose libvips centre option, mimics *magick +0.5px convention

lib/constructor.js

@@ -102,6 +102,7 @@ const Sharp = function (input, options) {
     withoutEnlargement: false,
     kernel: 'lanczos3',
     interpolator: 'bicubic',
+    centreSampling: false,
     // operations
     background: [0, 0, 0, 255],
     flatten: false,

lib/output.js

@@ -115,14 +115,14 @@ const jpeg = function jpeg (options) {
         throw new Error('Invalid chromaSubsampling (4:2:0, 4:4:4) ' + options.chromaSubsampling);
       }
     }
-    options.trellisQuantisation = options.trellisQuantisation || options.trellisQuantization;
+    options.trellisQuantisation = is.bool(options.trellisQuantization) ? options.trellisQuantization : options.trellisQuantisation;
     if (is.defined(options.trellisQuantisation)) {
       this._setBooleanOption('jpegTrellisQuantisation', options.trellisQuantisation);
     }
     if (is.defined(options.overshootDeringing)) {
       this._setBooleanOption('jpegOvershootDeringing', options.overshootDeringing);
     }
-    options.optimiseScans = is.bool(options.optimiseScans) ? options.optimiseScans : options.optimizeScans;
+    options.optimiseScans = is.bool(options.optimizeScans) ? options.optimizeScans : options.optimiseScans;
     if (is.defined(options.optimiseScans)) {
       this._setBooleanOption('jpegOptimiseScans', options.optimiseScans);
       if (options.optimiseScans) {

lib/resize.js

@@ -94,6 +94,8 @@ const interpolator = {
  * @param {Object} [options]
  * @param {String} [options.kernel='lanczos3'] - the kernel to use for image reduction.
  * @param {String} [options.interpolator='bicubic'] - the interpolator to use for image enlargement.
+ * @param {Boolean} [options.centreSampling=false] - use *magick centre sampling convention instead of corner sampling.
+ * @param {Boolean} [options.centerSampling=false] - alternative spelling of centreSampling.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
  */
@@ -133,6 +135,11 @@ const resize = function resize (width, height, options) {
         throw new Error('Invalid interpolator ' + options.interpolator);
       }
     }
+    // Centre sampling
+    options.centreSampling = is.bool(options.centerSampling) ? options.centerSampling : options.centreSampling;
+    if (is.defined(options.centreSampling)) {
+      this._setBooleanOption('centreSampling', options.centreSampling);
+    }
   }
   return this;
 };