From 8e17c6f518316eea1f30361083b42800e1c874a3 Mon Sep 17 00:00:00 2001
From: Kleis Auke Wolthuizen <github@kleisauke.nl>
Date: Tue, 13 May 2025 17:12:23 +0200
Subject: [PATCH] Prefer use of `vips_interpretation_max_alpha()`

This also ensures we handle scRGB correctly, see:
https://github.com/libvips/libvips/commit/e9c5a3155272b7328f5a0f1a21d0afcfbd1d7490
---
 src/common.cc | 10 +---------
 src/common.h  |  6 ------
 src/stats.cc  |  2 +-
 3 files changed, 2 insertions(+), 16 deletions(-)

diff --git a/src/common.cc b/src/common.cc
index 575b54e7..b00483c5 100644
--- a/src/common.cc
+++ b/src/common.cc
@@ -951,14 +951,6 @@ namespace sharp {
     return interpretation == VIPS_INTERPRETATION_RGB16 || interpretation == VIPS_INTERPRETATION_GREY16;
   }
 
-  /*
-    Return the image alpha maximum. Useful for combining alpha bands. scRGB
-    images are 0 - 1 for image data, but the alpha is 0 - 255.
-  */
-  double MaximumImageAlpha(VipsInterpretation const interpretation) {
-    return Is16Bit(interpretation) ? 65535.0 : 255.0;
-  }
-
   /*
     Convert RGBA value to another colourspace
   */
@@ -1033,7 +1025,7 @@ namespace sharp {
   VImage EnsureAlpha(VImage image, double const value) {
     if (!image.has_alpha()) {
       std::vector<double> alpha;
-      alpha.push_back(value * sharp::MaximumImageAlpha(image.interpretation()));
+      alpha.push_back(value * vips_interpretation_max_alpha(image.interpretation()));
       image = image.bandjoin_const(alpha);
     }
     return image;
diff --git a/src/common.h b/src/common.h
index bd942806..1a61e47d 100644
--- a/src/common.h
+++ b/src/common.h
@@ -357,12 +357,6 @@ namespace sharp {
   */
   bool Is16Bit(VipsInterpretation const interpretation);
 
-  /*
-    Return the image alpha maximum. Useful for combining alpha bands. scRGB
-    images are 0 - 1 for image data, but the alpha is 0 - 255.
-  */
-  double MaximumImageAlpha(VipsInterpretation const interpretation);
-
   /*
     Convert RGBA value to another colourspace
   */
diff --git a/src/stats.cc b/src/stats.cc
index 61df71a2..bc9b243c 100644
--- a/src/stats.cc
+++ b/src/stats.cc
@@ -60,7 +60,7 @@ class StatsWorker : public Napi::AsyncWorker {
         // Image is not opaque when alpha layer is present and contains a non-mamixa value
         if (image.has_alpha()) {
           double const minAlpha = static_cast<double>(stats.getpoint(STAT_MIN_INDEX, bands).front());
-          if (minAlpha != sharp::MaximumImageAlpha(image.interpretation())) {
+          if (minAlpha != vips_interpretation_max_alpha(image.interpretation())) {
             baton->isOpaque = false;
           }
         }