From cc37b59309d18cd5461e08e41fca97b04fff7015 Mon Sep 17 00:00:00 2001
From: Lovell Fuller <github@lovell.info>
Date: Mon, 22 Feb 2021 12:32:20 +0000
Subject: [PATCH] Switch to libvips' recently-exposed has_alpha #2569

---
 docs/changelog.md | 3 +++
 src/common.cc     | 7 +------
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/docs/changelog.md b/docs/changelog.md
index 4fb2cde9..72e05cd4 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -6,6 +6,9 @@ Requires libvips v8.10.5
 
 ### v0.27.2 - TBD
 
+* Improve 16-bit grey+alpha support by using libvips' `has_alpha` detection.
+  [#2569](https://github.com/lovell/sharp/issues/2569)
+
 * Allow the use of non lower case extensions with `toFormat`.
   [#2581](https://github.com/lovell/sharp/pull/2581)
   [@florian-busch](https://github.com/florian-busch)
diff --git a/src/common.cc b/src/common.cc
index 2e761466..cc38a8da 100644
--- a/src/common.cc
+++ b/src/common.cc
@@ -421,12 +421,7 @@ namespace sharp {
     Uses colour space interpretation with number of channels to guess this.
   */
   bool HasAlpha(VImage image) {
-    int const bands = image.bands();
-    VipsInterpretation const interpretation = image.interpretation();
-    return (
-      (bands == 2 && interpretation == VIPS_INTERPRETATION_B_W) ||
-      (bands == 4 && interpretation != VIPS_INTERPRETATION_CMYK) ||
-      (bands == 5 && interpretation == VIPS_INTERPRETATION_CMYK));
+    return image.has_alpha();
   }
 
   /*