Expose erode and dilate operations #4243

Author: qpincon

docs/public/humans.txt

@@ -314,3 +314,6 @@ GitHub: https://github.com/happycollision
 
 Name: Florent Zabera
 GitHub: https://github.com/florentzabera
+
+Name: Quentin Pinçon
+GitHub: https://github.com/qpincon

docs/src/content/docs/api-operation.md

@@ -284,6 +284,52 @@ const gaussianBlurred = await sharp(input)
 ```
 
 
+## dilate
+> dilate([width]) ⇒ <code>Sharp</code>
+
+Expand foreground objects using the dilate morphological operator.
+
+
+**Throws**:
+
+- <code>Error</code> Invalid parameters
+
+
+| Param | Type | Default | Description |
+| --- | --- | --- | --- |
+| [width] | <code>Number</code> | <code>1</code> | dilation width in pixels. |
+
+**Example**  
+```js
+const output = await sharp(input)
+  .dilate()
+  .toBuffer();
+```
+
+
+## erode
+> erode([width]) ⇒ <code>Sharp</code>
+
+Shrink foreground objects using the erode morphological operator.
+
+
+**Throws**:
+
+- <code>Error</code> Invalid parameters
+
+
+| Param | Type | Default | Description |
+| --- | --- | --- | --- |
+| [width] | <code>Number</code> | <code>1</code> | erosion width in pixels. |
+
+**Example**  
+```js
+const output = await sharp(input)
+  .erode()
+  .toBuffer();
+```
+
+
 ## flatten
 > flatten([options]) ⇒ <code>Sharp</code>
 

docs/src/content/docs/changelog.md

@@ -45,6 +45,10 @@ Requires libvips v8.16.1
   [#4207](https://github.com/lovell/sharp/pull/4207)
   [@calebmer](https://github.com/calebmer)
 
+* Expose erode and dilate operations.
+  [#4243](https://github.com/lovell/sharp/pull/4243)
+  [@qpincon](https://github.com/qpincon)
+
 * Add support for RGBE images. Requires libvips compiled with radiance support.
   [#4316](https://github.com/lovell/sharp/pull/4316)
   [@florentzabera](https://github.com/florentzabera)

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,

src/operations.cc

@@ -472,4 +472,26 @@ namespace sharp {
     }
   }
 
+  /*
+   * Dilate an image
+   */
+  VImage Dilate(VImage image, int const width) {
+    int const maskWidth = 2 * width + 1;
+    VImage mask = VImage::new_matrix(maskWidth, maskWidth);
+    return image.morph(
+      mask,
+      VIPS_OPERATION_MORPHOLOGY_DILATE).invert();
+  }
+
+  /*
+   * Erode an image
+   */
+  VImage Erode(VImage image, int const width) {
+    int const maskWidth = 2 * width + 1;
+    VImage mask = VImage::new_matrix(maskWidth, maskWidth);
+    return image.morph(
+      mask,
+      VIPS_OPERATION_MORPHOLOGY_ERODE).invert();
+  }
+
 }  // namespace sharp

src/operations.h

@@ -120,6 +120,15 @@ namespace sharp {
   VImage EmbedMultiPage(VImage image, int left, int top, int width, int height,
                         VipsExtend extendWith, std::vector<double> background, int nPages, int *pageHeight);
 
+  /*
+   * Dilate an image
+   */
+  VImage Dilate(VImage image, int const maskWidth);
+
+  /*
+   * Erode an image
+   */
+  VImage Erode(VImage image, int const maskWidth);
 }  // namespace sharp
 
 #endif  // SRC_OPERATIONS_H_

src/pipeline.cc

@@ -609,6 +609,16 @@ class PipelineWorker : public Napi::AsyncWorker {
         image = sharp::Threshold(image, baton->threshold, baton->thresholdGrayscale);
       }
 
+      // Dilate - must happen before blurring, due to the utility of dilating after thresholding
+      if (baton->dilateWidth != 0) {
+        image = sharp::Dilate(image, baton->dilateWidth);
+      }
+
+      // Erode - must happen before blurring, due to the utility of eroding after thresholding
+      if (baton->erodeWidth != 0) {
+        image = sharp::Erode(image, baton->erodeWidth);
+      }
+
       // Blur
       if (shouldBlur) {
         image = sharp::Blur(image, baton->blurSigma, baton->precision, baton->minAmpl);
@@ -1621,6 +1631,8 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->gammaOut = sharp::AttrAsDouble(options, "gammaOut");
   baton->linearA = sharp::AttrAsVectorOfDouble(options, "linearA");
   baton->linearB = sharp::AttrAsVectorOfDouble(options, "linearB");
+  baton->dilateWidth = sharp::AttrAsUint32(options, "dilateWidth");
+  baton->erodeWidth = sharp::AttrAsUint32(options, "erodeWidth");
   baton->greyscale = sharp::AttrAsBool(options, "greyscale");
   baton->normalise = sharp::AttrAsBool(options, "normalise");
   baton->normaliseLower = sharp::AttrAsUint32(options, "normaliseLower");

src/pipeline.h

@@ -101,6 +101,8 @@ struct PipelineBaton {
   int trimOffsetTop;
   std::vector<double> linearA;
   std::vector<double> linearB;
+  int dilateWidth;
+  int erodeWidth;
   double gamma;
   double gammaOut;
   bool greyscale;
@@ -274,6 +276,8 @@ struct PipelineBaton {
     trimOffsetTop(0),
     linearA{},
     linearB{},
+    dilateWidth(0),
+    erodeWidth(0),
     gamma(0.0),
     greyscale(false),
     normalise(false),