Add withoutReduction option to resize operation (#3006)

lib/constructor.js

@@ -166,6 +166,7 @@ const Sharp = function (input, options) {
     extendRight: 0,
     extendBackground: [0, 0, 0, 255],
     withoutEnlargement: false,
+    withoutReduction: false,
     affineMatrix: [],
     affineBackground: [0, 0, 0, 255],
     affineIdx: 0,

lib/resize.js

@@ -183,6 +183,20 @@ function isRotationExpected (options) {
  *   });
  *
  * @example
+ * sharp(input)
+ *   .resize(200, 200, {
+ *     fit: sharp.fit.outside,
+ *     withoutReduction: true
+ *   })
+ *   .toFormat('jpeg')
+ *   .toBuffer()
+ *   .then(function(outputBuffer) {
+ *     // outputBuffer contains JPEG image data
+ *     // of at least 200 pixels wide and 200 pixels high while maintaining aspect ratio
+ *     // and no smaller than the input image
+ *   });
+ *
+ * @example
  * const scaleByHalf = await sharp(input)
  *   .metadata()
  *   .then(({ width }) => sharp(input)
@@ -200,6 +214,7 @@ function isRotationExpected (options) {
  * @param {String|Object} [options.background={r: 0, g: 0, b: 0, alpha: 1}] - background colour when using a `fit` of `contain`, parsed by the [color](https://www.npmjs.org/package/color) module, defaults to black without transparency.
  * @param {String} [options.kernel='lanczos3'] - the kernel to use for image reduction.
  * @param {Boolean} [options.withoutEnlargement=false] - do not enlarge if the width *or* height are already less than the specified dimensions, equivalent to GraphicsMagick's `>` geometry option.
+ * @param {Boolean} [options.withoutReduction=false] - do not reduce if the width *or* height are already greater than the specified dimensions, equivalent to GraphicsMagick's `<` geometry option.
  * @param {Boolean} [options.fastShrinkOnLoad=true] - take greater advantage of the JPEG and WebP shrink-on-load feature, which can lead to a slight moiré pattern on some images.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
@@ -276,6 +291,10 @@ function resize (width, height, options) {
     if (is.defined(options.withoutEnlargement)) {
       this._setBooleanOption('withoutEnlargement', options.withoutEnlargement);
     }
+    // Without reduction
+    if (is.defined(options.withoutReduction)) {
+      this._setBooleanOption('withoutReduction', options.withoutReduction);
+    }
     // Shrink on load
     if (is.defined(options.fastShrinkOnLoad)) {
       this._setBooleanOption('fastShrinkOnLoad', options.fastShrinkOnLoad);