Expose erode and dilate operations #4243

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),