Ensure correct Gaussian blur before affine #121

Use double sigma instead of int radius for blur

README.md

@@ -319,13 +319,13 @@ Do not enlarge the output image if the input image width *or* height are already
 
 This is equivalent to GraphicsMagick's `>` geometry option: "change the dimensions of the image only if its width or height exceeds the geometry specification".
 
-#### blur([radius])
+#### blur([sigma])
 
 When used without parameters, performs a fast, mild blur of the output image. This typically reduces performance by 10%.
 
-When a `radius` is provided, performs a slower, more accurate Gaussian blur. This typically reduces performance by 30%.
+When a `sigma` is provided, performs a slower, more accurate Gaussian blur. This typically reduces performance by 25%.
 
-* `radius`, if present, is an integral Number representing the approximate blur mask radius in pixels.
+* `sigma`, if present, is a Number between 0.3 and 1000 representing the approximate blur radius in pixels.
 
 #### sharpen([radius], [flat], [jagged])
 

index.js

@@ -43,7 +43,7 @@ var Sharp = function(input) {
     // operations
     background: [0, 0, 0, 255],
     flatten: false,
-    blurRadius: 0,
+    blurSigma: 0,
     sharpenRadius: 0,
     sharpenFlat: 1,
     sharpenJagged: 2,
@@ -208,21 +208,21 @@ Sharp.prototype.withoutEnlargement = function(withoutEnlargement) {
 
 /*
   Blur the output image.
-  Call without a radius to use a fast, mild blur.
-  Call with a radius to use a slower, more accurate Gaussian blur.
+  Call without a sigma to use a fast, mild blur.
+  Call with a sigma to use a slower, more accurate Gaussian blur.
 */
-Sharp.prototype.blur = function(radius) {
-  if (typeof radius === 'undefined') {
+Sharp.prototype.blur = function(sigma) {
+  if (typeof sigma === 'undefined') {
     // No arguments: default to mild blur
-    this.options.blurRadius = -1;
-  } else if (typeof radius === 'boolean') {
+    this.options.blurSigma = -1;
+  } else if (typeof sigma === 'boolean') {
     // Boolean argument: apply mild blur?
-    this.options.blurRadius = radius ? -1 : 0;
-  } else if (typeof radius === 'number' && !Number.isNaN(radius) && (radius % 1 === 0) && radius >= 1) {
-    // Numeric argument: specific radius
-    this.options.blurRadius = radius;
+    this.options.blurSigma = sigma ? -1 : 0;
+  } else if (typeof sigma === 'number' && !Number.isNaN(sigma) && sigma >= 0.3 && sigma <= 1000) {
+    // Numeric argument: specific sigma
+    this.options.blurSigma = sigma;
   } else {
-    throw new Error('Invalid blur radius ' + radius + ' (expected integer >= 1)');
+    throw new Error('Invalid blur sigma (0.3 to 1000.0) ' + sigma);
   }
   return this;
 };

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sharp",
-  "version": "0.8.0",
+  "version": "0.8.1",
   "author": "Lovell Fuller <npm@lovell.info>",
   "contributors": [
     "Pierre Inglebert <pierre.inglebert@gmail.com>",

src/resize.cc

@@ -51,7 +51,7 @@ struct ResizeBaton {
   std::string interpolator;
   double background[4];
   bool flatten;
-  int blurRadius;
+  double blurSigma;
   int sharpenRadius;
   double sharpenFlat;
   double sharpenJagged;
@@ -78,7 +78,7 @@ struct ResizeBaton {
     canvas(Canvas::CROP),
     gravity(0),
     flatten(false),
-    blurRadius(0),
+    blurSigma(0.0),
     sharpenRadius(0),
     sharpenFlat(1.0),
     sharpenJagged(2.0),
@@ -364,22 +364,33 @@ class ResizeWorker : public NanAsyncWorker {
     }
 
     // Use vips_affine with the remaining float part
-    if (residual != 0) {
-      // Apply variable blur radius of floor(residual) before large affine reductions
-      if (residual >= 1) {
-        VipsImage *blurred;
-        if (vips_gaussblur(image, &blurred, floor(residual), NULL)) {
-          return Error(baton, hook);
+    if (residual != 0.0) {
+      // Apply Gaussian blur before large affine reductions
+      if (residual < 1.0) {
+        // Calculate standard deviation
+        double sigma = ((1.0 / residual) - 0.5) / 1.5;
+        if (sigma >= 0.3) {
+          // Create Gaussian function for standard deviation
+          VipsImage *gaussian;
+          if (vips_gaussmat(&gaussian, sigma, 0.2, "separable", TRUE, "integer", TRUE, NULL)) {
+            return Error(baton, hook);
+          }
+          vips_object_local(hook, gaussian);
+          // Apply Gaussian function
+          VipsImage *blurred;
+          if (vips_convsep(image, &blurred, gaussian, "precision", VIPS_PRECISION_INTEGER, NULL)) {
+            return Error(baton, hook);
+          }
+          vips_object_local(hook, blurred);
+          image = blurred;
         }
-        vips_object_local(hook, blurred);
-        image = blurred;
       }
       // Create interpolator - "bilinear" (default), "bicubic" or "nohalo"
       VipsInterpolate *interpolator = vips_interpolate_new(baton->interpolator.c_str());
       vips_object_local(hook, interpolator);
       // Perform affine transformation
       VipsImage *affined;
-      if (vips_affine(image, &affined, residual, 0, 0, residual, "interpolate", interpolator, NULL)) {
+      if (vips_affine(image, &affined, residual, 0.0, 0.0, residual, "interpolate", interpolator, NULL)) {
         return Error(baton, hook);
       }
       vips_object_local(hook, affined);
@@ -502,10 +513,10 @@ class ResizeWorker : public NanAsyncWorker {
     }
 
     // Blur
-    if (baton->blurRadius != 0) {
+    if (baton->blurSigma != 0.0) {
       VipsImage *blurred;
-      if (baton->blurRadius == -1) {
-        // Fast, mild blur
+      if (baton->blurSigma < 0.0) {
+        // Fast, mild blur - averages neighbouring pixels
         VipsImage *blur = vips_image_new_matrixv(3, 3,
           1.0, 1.0, 1.0,
           1.0, 1.0, 1.0,
@@ -517,7 +528,15 @@ class ResizeWorker : public NanAsyncWorker {
         }
       } else {
         // Slower, accurate Gaussian blur
-        if (vips_gaussblur(image, &blurred, baton->blurRadius, NULL)) {
+        // Create Gaussian function for standard deviation
+        VipsImage *gaussian;
+        if (vips_gaussmat(&gaussian, baton->blurSigma, 0.2, "separable", TRUE, "integer", TRUE, NULL)) {
+          return Error(baton, hook);
+        }
+        vips_object_local(hook, gaussian);
+        // Apply Gaussian function
+        VipsImage *blurred;
+        if (vips_convsep(image, &blurred, gaussian, "precision", VIPS_PRECISION_INTEGER, NULL)) {
           return Error(baton, hook);
         }
       }
@@ -847,7 +866,7 @@ NAN_METHOD(resize) {
   baton->interpolator = *String::Utf8Value(options->Get(NanNew<String>("interpolator"))->ToString());
   // Operators
   baton->flatten = options->Get(NanNew<String>("flatten"))->BooleanValue();
-  baton->blurRadius = options->Get(NanNew<String>("blurRadius"))->Int32Value();
+  baton->blurSigma = options->Get(NanNew<String>("blurSigma"))->NumberValue();
   baton->sharpenRadius = options->Get(NanNew<String>("sharpenRadius"))->Int32Value();
   baton->sharpenFlat = options->Get(NanNew<String>("sharpenFlat"))->NumberValue();
   baton->sharpenJagged = options->Get(NanNew<String>("sharpenJagged"))->NumberValue();

test/unit/blur.js

@@ -35,11 +35,11 @@ describe('Blur', function() {
       });
   });
 
-  it('specific radius 100', function(done) {
+  it('specific radius 0.3', function(done) {
     sharp(fixtures.inputJpg)
       .resize(320, 240)
-      .blur(100)
-      .toFile(fixtures.path('output.blur-100.jpg'), function(err, info) {
+      .blur(0.3)
+      .toFile(fixtures.path('output.blur-0.3.jpg'), function(err, info) {
         if (err) throw err;
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(320, info.width);
@@ -64,7 +64,7 @@ describe('Blur', function() {
   it('invalid radius', function(done) {
     var isValid = true;
     try {
-      sharp(fixtures.inputJpg).blur(1.5);
+      sharp(fixtures.inputJpg).blur(0.1);
     } catch (err) {
       isValid = false;
     }

test/unit/io.js

@@ -370,7 +370,7 @@ describe('Input/output', function() {
     });
 
     if (semver.gte(sharp.libvipsVersion(), '7.41.0')) {
-      it('withoutAdaptiveFiltering generates smaller file [libvips 7.41.0+]', function(done) {
+      it('withoutAdaptiveFiltering generates smaller file [libvips ' + sharp.libvipsVersion() + '>=7.41.0]', function(done) {
         // First generate with adaptive filtering
         sharp(fixtures.inputPng)
           .resize(320, 240)
@@ -401,7 +401,7 @@ describe('Input/output', function() {
   });
 
   if (semver.gte(sharp.libvipsVersion(), '7.40.0')) {
-    it('Load TIFF from Buffer [libvips 7.40.0+]', function(done) {
+    it('Load TIFF from Buffer [libvips ' + sharp.libvipsVersion() + '>=7.40.0]', function(done) {
       var inputTiffBuffer = fs.readFileSync(fixtures.inputTiff);
       sharp(inputTiffBuffer)
         .resize(320, 240)