From b369c4bb8a52db0072b46cffd974d4964ff12860 Mon Sep 17 00:00:00 2001
From: Lovell Fuller <github@lovell.info>
Date: Thu, 17 Sep 2020 11:08:52 +0100
Subject: [PATCH] Ensure stats can be calculated for 1x1 input #2372

---
 docs/changelog.md  |  3 +++
 src/stats.cc       | 14 ++++++++------
 test/unit/stats.js | 13 +++++++++++++
 3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/docs/changelog.md b/docs/changelog.md
index b0c2dd14..1364a70f 100644
--- a/docs/changelog.md
+++ b/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+.
diff --git a/src/stats.cc b/src/stats.cc
index bc5ee13e..1d7942b1 100644
--- a/src/stats.cc
+++ b/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
-        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();
+        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)
diff --git a/test/unit/stats.js b/test/unit/stats.js
index b456ca9c..6b1d8ee5 100644
--- a/test/unit/stats.js
+++ b/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) {