Expose optional minAmplitude parameter of blur operation (#4172)

src/operations.cc

@@ -144,7 +144,7 @@ namespace sharp {
   /*
    * Gaussian blur. Use sigma of -1.0 for fast blur.
    */
-  VImage Blur(VImage image, double const sigma, VipsPrecision precision) {
+  VImage Blur(VImage image, double const sigma, VipsPrecision precision, double const minAmpl) {
     if (sigma == -1.0) {
       // Fast, mild blur - averages neighbouring pixels
       VImage blur = VImage::new_matrixv(3, 3,
@@ -156,7 +156,8 @@ namespace sharp {
     } else {
       // Slower, accurate Gaussian blur
       return StaySequential(image).gaussblur(sigma, VImage::option()
-        ->set("precision", precision));
+        ->set("precision", precision)
+        ->set("min_ampl", minAmpl));
     }
   }
 

src/operations.h

@@ -47,7 +47,7 @@ namespace sharp {
   /*
    * Gaussian blur. Use sigma of -1.0 for fast blur.
    */
-  VImage Blur(VImage image, double const sigma, VipsPrecision precision);
+  VImage Blur(VImage image, double const sigma, VipsPrecision precision, double const minAmpl);
 
   /*
    * Convolution with a kernel.

src/pipeline.cc

@@ -592,7 +592,7 @@ class PipelineWorker : public Napi::AsyncWorker {
 
       // Blur
       if (shouldBlur) {
-        image = sharp::Blur(image, baton->blurSigma, baton->precision);
+        image = sharp::Blur(image, baton->blurSigma, baton->precision, baton->minAmpl);
       }
 
       // Unflatten the image
@@ -1542,6 +1542,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->negateAlpha = sharp::AttrAsBool(options, "negateAlpha");
   baton->blurSigma = sharp::AttrAsDouble(options, "blurSigma");
   baton->precision = sharp::AttrAsEnum<VipsPrecision>(options, "precision", VIPS_TYPE_PRECISION);
+  baton->minAmpl = sharp::AttrAsDouble(options, "minAmpl");
   baton->brightness = sharp::AttrAsDouble(options, "brightness");
   baton->saturation = sharp::AttrAsDouble(options, "saturation");
   baton->hue = sharp::AttrAsInt32(options, "hue");

src/pipeline.h

@@ -79,6 +79,7 @@ struct PipelineBaton {
   bool negateAlpha;
   double blurSigma;
   VipsPrecision precision;
+  double minAmpl;
   double brightness;
   double saturation;
   int hue;