Expose optional minAmpl parameter of blur operation

docs/api-operation.md

@@ -250,6 +250,7 @@ When a `sigma` is provided, performs a slower, more accurate Gaussian blur.
 | [options] | <code>Object</code> \| <code>number</code> \| <code>Boolean</code> |  |  |
 | [options.sigma] | <code>number</code> |  | a value between 0.3 and 1000 representing the sigma of the Gaussian mask, where `sigma = 1 + radius / 2`. |
 | [options.precision] | <code>string</code> | <code>&quot;&#x27;integer&#x27;&quot;</code> | How accurate the operation should be, one of: integer, float, approximate. |
+| [options.minAmplitude] | <code>number</code> | <code>0.2</code> | A value between 0.001 and 1. A smaller value will generate a larger, more accurate mask. |
 
 **Example**  
 ```js

lib/constructor.js

@@ -227,6 +227,7 @@ const Sharp = function (input, options) {
     medianSize: 0,
     blurSigma: 0,
     precision: 'integer',
+    minAmpl: 0.2,
     sharpenSigma: 0,
     sharpenM1: 1,
     sharpenM2: 2,

lib/index.d.ts

@@ -1347,6 +1347,8 @@ declare namespace sharp {
     interface BlurOptions {
         /** A value between 0.3 and 1000 representing the sigma of the Gaussian mask, where `sigma = 1 + radius / 2` */
         sigma: number;
+        /** A value between 0.001 and 1. A smaller value will generate a larger, more accurate mask. */
+        minAmplitude?: number;
         /** How accurate the operation should be, one of: integer, float, approximate. (optional, default "integer") */
         precision?: Precision | undefined;
     }

lib/operation.js

@@ -381,6 +381,7 @@ function median (size) {
  * @param {Object|number|Boolean} [options]
  * @param {number} [options.sigma] a value between 0.3 and 1000 representing the sigma of the Gaussian mask, where `sigma = 1 + radius / 2`.
  * @param {string} [options.precision='integer'] How accurate the operation should be, one of: integer, float, approximate.
+ * @param {number} [options.minAmplitude=0.2] A value between 0.001 and 1. A smaller value will generate a larger, more accurate mask.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
  */
@@ -400,6 +401,13 @@ function blur (options) {
         throw is.invalidParameterError('precision', 'one of: integer, float, approximate', options.precision);
       }
     }
+    if ('minAmplitude' in options) {
+      if (is.number(options.minAmplitude) && is.inRange(options.minAmplitude, 0.001, 1)) {
+        this.options.minAmpl = options.minAmplitude;
+      } else {
+        throw is.invalidParameterError('minAmplitude', 'number between 0.001 and 1', options.minAmplitude);
+      }
+    }
   }
 
   if (!is.defined(options)) {

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;

test/types/sharp.test-d.ts

@@ -63,6 +63,7 @@ sharp().blur();
 sharp().blur(1);
 sharp().blur({ sigma: 1 });
 sharp().blur({ sigma: 1, precision: 'approximate' });
+sharp().blur({ sigma: 1, minAmplitude: 0.8 });
 
 sharp({
   create: {

test/unit/blur.js

@@ -111,6 +111,16 @@ describe('Blur', function () {
     }, /Expected one of: integer, float, approximate for precision but received invalid of type string/);
   });
 
+  it('invalid minAmplitude', function () {
+    assert.throws(function () {
+      sharp(fixtures.inputJpg).blur({ sigma: 1, minAmplitude: 0 });
+    }, /Expected number between 0.001 and 1 for minAmplitude but received 0 of type number/);
+
+    assert.throws(function () {
+      sharp(fixtures.inputJpg).blur({ sigma: 1, minAmplitude: 1.01 });
+    }, /Expected number between 0.001 and 1 for minAmplitude but received 1.01 of type number/);
+  });
+
   it('specific radius 10 and precision approximate', async () => {
     const approximate = await sharp(fixtures.inputJpg)
       .resize(320, 240)
@@ -125,6 +135,20 @@ describe('Blur', function () {
     await fixtures.assertSimilar(fixtures.expected('blur-10.jpg'), approximate);
   });
 
+  it('specific radius 10 and minAmplitude 0.01', async () => {
+    const minAmplitudeLow = await sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .blur({ sigma: 10, minAmplitude: 0.01 })
+      .toBuffer();
+    const minAmplitudeDefault = await sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .blur(10)
+      .toBuffer();
+
+    assert.notDeepEqual(minAmplitudeLow, minAmplitudeDefault);
+    await fixtures.assertSimilar(fixtures.expected('blur-10.jpg'), minAmplitudeLow);
+  });
+
   it('options.sigma is required if options object is passed', function () {
     assert.throws(function () {
       sharp(fixtures.inputJpg).blur({ precision: 'invalid' });