From 37161bf05d0bba22ebde81a6b7e7d7393f67c84b Mon Sep 17 00:00:00 2001
From: Andrew <andrew@digerati.co.nz>
Date: Mon, 28 Nov 2022 18:50:04 +1300
Subject: [PATCH] Make sure correct bKGD is retained

---
 src/reduction/mod.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/reduction/mod.rs b/src/reduction/mod.rs
index 89aec38b..8fd258f7 100644
--- a/src/reduction/mod.rs
+++ b/src/reduction/mod.rs
@@ -76,6 +76,13 @@ pub fn reduced_palette(png: &PngImage) -> Option<PngImage> {
             color_val(a.0).cmp(&color_val(b.0))
         });
 
+        // Make sure the background is also included, but only after sorting since it may not be used in idat
+        if let Some(&idx) = png.aux_headers.get(b"bKGD").and_then(|b| b.first()) {
+            if !used[idx as usize] {
+                used_enumerated.push((idx as usize, &true));
+            }
+        }
+
         let mut next_index = 0_u16;
         let mut seen = IndexMap::with_capacity(palette.len());
         for (i, used) in used_enumerated.iter().cloned() {