Ensure stats can be calculated for 1x1 input #2372

docs/changelog.md

@@ -18,6 +18,9 @@ Requires libvips v8.10.0
   [#2369](https://github.com/lovell/sharp/pull/2369)
   [@AcrylicShrimp](https://github.com/AcrylicShrimp)
 
+* Ensure `stats` can be calculated for 1x1 input.
+  [#2372](https://github.com/lovell/sharp/issues/2372)
+
 ### v0.26.0 - 25th August 2020
 
 * Prebuilt libvips binaries are now statically-linked and Brotli-compressed, requiring Node.js 10.16.0+.

src/stats.cc

@@ -80,12 +80,14 @@ class StatsWorker : public Napi::AsyncWorker {
         // Estimate entropy via histogram of greyscale value frequency
         baton->entropy = std::abs(greyscale.hist_find().hist_entropy());
         // Estimate sharpness via standard deviation of greyscale laplacian
+        if (image.width() > 1 || image.height() > 1) {
           VImage laplacian = VImage::new_matrixv(3, 3,
             0.0,  1.0, 0.0,
             1.0, -4.0, 1.0,
             0.0,  1.0, 0.0);
           laplacian.set("scale", 9.0);
           baton->sharpness = greyscale.conv(laplacian).deviate();
+        }
         // Most dominant sRGB colour via 4096-bin 3D histogram
         vips::VImage hist = sharp::RemoveAlpha(image)
           .colourspace(VIPS_INTERPRETATION_sRGB)

test/unit/stats.js

@@ -462,6 +462,19 @@ describe('Image Stats', function () {
       })
   );
 
+  it('Entropy and sharpness of 1x1 input are zero', async () => {
+    const { entropy, sharpness } = await sharp({
+      create: {
+        width: 1,
+        height: 1,
+        channels: 3,
+        background: 'red'
+      }
+    }).stats();
+    assert.strictEqual(entropy, 0);
+    assert.strictEqual(sharpness, 0);
+  });
+
   it('Stream in, Callback out', function (done) {
     const readable = fs.createReadStream(fixtures.inputJpg);
     const pipeline = sharp().stats(function (err, stats) {