Expose erode and dilate operations #4243

lib/constructor.js

@@ -263,6 +263,8 @@ const Sharp = function (input, options) {
     trimBackground: [],
     trimThreshold: -1,
     trimLineArt: false,
+    dilateWidth: 0,
+    erodeWidth: 0,
     gamma: 0,
     gammaOut: 0,
     greyscale: false,

lib/index.d.ts

@@ -504,6 +504,22 @@ declare namespace sharp {
          */
         blur(sigma?: number | boolean | BlurOptions): Sharp;
 
+        /**
+         * Expand foreground objects using the dilate morphological operator.
+         * @param {Number} [width=1] dilation width in pixels.
+         * @throws {Error} Invalid parameters
+         * @returns A sharp instance that can be used to chain operations
+         */
+        dilate(width?: number): Sharp;
+
+        /**
+         * Shrink foreground objects using the erode morphological operator.
+         * @param {Number} [width=1] erosion width in pixels.
+         * @throws {Error} Invalid parameters
+         * @returns A sharp instance that can be used to chain operations
+         */
+        erode(width?: number): Sharp;
+
         /**
          * Merge alpha transparency channel, if any, with background.
          * @param flatten true to enable and false to disable (defaults to true)

lib/operation.js

@@ -443,6 +443,52 @@ function blur (options) {
   return this;
 }
 
+/**
+ * Expand foreground objects using the dilate morphological operator.
+ *
+ * @example
+ * const output = await sharp(input)
+ *   .dilate()
+ *   .toBuffer();
+ *
+ * @param {Number} [width=1] dilation width in pixels.
+ * @returns {Sharp}
+ * @throws {Error} Invalid parameters
+ */
+function dilate (width) {
+  if (!is.defined(width)) {
+    this.options.dilateWidth = 1;
+  } else if (is.integer(width) && width > 0) {
+    this.options.dilateWidth = width;
+  } else {
+    throw is.invalidParameterError('dilate', 'positive integer', dilate);
+  }
+  return this;
+}
+
+/**
+ * Shrink foreground objects using the erode morphological operator.
+ *
+ * @example
+ * const output = await sharp(input)
+ *   .erode()
+ *   .toBuffer();
+ *
+ * @param {Number} [width=1] erosion width in pixels.
+ * @returns {Sharp}
+ * @throws {Error} Invalid parameters
+ */
+function erode (width) {
+  if (!is.defined(width)) {
+    this.options.erodeWidth = 1;
+  } else if (is.integer(width) && width > 0) {
+    this.options.erodeWidth = width;
+  } else {
+    throw is.invalidParameterError('erode', 'positive integer', erode);
+  }
+  return this;
+}
+
 /**
  * Merge alpha transparency channel, if any, with a background, then remove the alpha channel.
  *
@@ -958,6 +1004,8 @@ module.exports = function (Sharp) {
     flop,
     affine,
     sharpen,
+    erode,
+    dilate,
     median,
     blur,
     flatten,