Improve perf/accuracy of nearest neighbour integral upsample

docs/changelog.md

@@ -14,6 +14,10 @@ Requires libvips v8.5.2.
   [#607](https://github.com/lovell/sharp/issues/607)
   [@puzrin](https://github.com/puzrin)
 
+* Improve performance and accuracy of nearest neighbour integral upsampling.
+  [#752](https://github.com/lovell/sharp/issues/752)
+  [@MrIbby](https://github.com/MrIbby)
+
 * Ensure ARM64 pre-built binaries use correct C++11 ABI version.
   [#772](https://github.com/lovell/sharp/issues/772)
   [@ajiratech2](https://github.com/ajiratech2)

src/pipeline.cc

@@ -417,19 +417,27 @@ class PipelineWorker : public Nan::AsyncWorker {
               ->set("centre", baton->centreSampling));
           }
         }
-        // Perform affine enlargement
+        // Perform enlargement
         if (yresidual > 1.0 || xresidual > 1.0) {
+          if (trunc(xresidual) == xresidual && trunc(yresidual) == yresidual && baton->interpolator == "nearest") {
+            // Fast, integral nearest neighbour enlargement
+            image = image.zoom(xresidual, yresidual);
+          } else {
+            // Floating point affine transformation
             vips::VInterpolate interpolator = vips::VInterpolate::new_from_name(baton->interpolator.data());
-          if (yresidual > 1.0) {
+            if (yresidual > 1.0 && xresidual > 1.0) {
+              image = image.affine({xresidual, 0.0, 0.0, yresidual}, VImage::option()
+                ->set("interpolate", interpolator));
+            } else if (yresidual > 1.0) {
               image = image.affine({1.0, 0.0, 0.0, yresidual}, VImage::option()
                 ->set("interpolate", interpolator));
-          }
+            } else if (xresidual > 1.0) {
-          if (xresidual > 1.0) {
               image = image.affine({xresidual, 0.0, 0.0, 1.0}, VImage::option()
                 ->set("interpolate", interpolator));
             }
           }
         }
+      }
 
       // Rotate
       if (!baton->rotateBeforePreExtract && rotation != VIPS_ANGLE_D0) {

test/unit/interpolation.js

@@ -35,16 +35,53 @@ describe('Interpolators and kernels', function () {
       sharp.interpolator.locallyBoundedBicubic,
       sharp.interpolator.vertexSplitQuadraticBasisSpline
     ].forEach(function (interpolator) {
-      it(interpolator, function (done) {
+      describe(interpolator, function () {
-        sharp(fixtures.inputJpg)
+        it('x and y', function (done) {
-          .resize(320, null, { interpolator: interpolator })
+          sharp(fixtures.inputTiff8BitDepth)
+            .resize(200, 200, { interpolator: interpolator })
+            .png()
             .toBuffer(function (err, data, info) {
               if (err) throw err;
-            assert.strictEqual('jpeg', info.format);
+              assert.strictEqual(200, info.width);
-            assert.strictEqual(320, info.width);
+              assert.strictEqual(200, info.height);
-            fixtures.assertSimilar(fixtures.inputJpg, data, done);
+              done();
             });
         });
+        it('x only', function (done) {
+          sharp(fixtures.inputTiff8BitDepth)
+            .resize(200, 21, { interpolator: interpolator })
+            .png()
+            .toBuffer(function (err, data, info) {
+              if (err) throw err;
+              assert.strictEqual(200, info.width);
+              assert.strictEqual(21, info.height);
+              done();
+            });
+        });
+        it('y only', function (done) {
+          sharp(fixtures.inputTiff8BitDepth)
+            .resize(21, 200, { interpolator: interpolator })
+            .png()
+            .toBuffer(function (err, data, info) {
+              if (err) throw err;
+              assert.strictEqual(21, info.width);
+              assert.strictEqual(200, info.height);
+              done();
+            });
+        });
+      });
+    });
+
+    it('nearest with integral factor', function (done) {
+      sharp(fixtures.inputTiff8BitDepth)
+        .resize(210, 210, { interpolator: 'nearest' })
+        .png()
+        .toBuffer(function (err, data, info) {
+          if (err) throw err;
+          assert.strictEqual(210, info.width);
+          assert.strictEqual(210, info.height);
+          done();
+        });
     });
   });