From 7100b0d6177aece0eeb1f521cafaca9e6ba18fd4 Mon Sep 17 00:00:00 2001
From: MikeeI <MikeeI@users.noreply.github.com>
Date: Mon, 5 Oct 2026 07:00:19 +0200
Subject: [PATCH] fix(io): preserve HDR samples when unmatting PSD composites
 (#106)

---
 crates/io/src/lib.rs             | 2 +-
 crates/io/src/pixels.rs          | 3 ++-
 crates/io/tests/psd_structure.rs | 9 +++++++++
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/crates/io/src/lib.rs b/crates/io/src/lib.rs
index c4cb637e..162c2872 100644
--- a/crates/io/src/lib.rs
+++ b/crates/io/src/lib.rs
@@ -167,7 +167,7 @@ pub fn merged_composite(file: &PsdFile) -> Result<Vec<[f32; 4]>, IoError> {
                 let mut v: [f32; 4] = std::array::from_fn(|i| f32::from(p[i]) / 255.0);
                 if unmatte {
                     for c in 0..3 {
-                        v[c] = pixels::unmatte(v[c], v[3], 1.0);
+                        v[c] = pixels::unmatte(v[c], v[3], 1.0).clamp(0.0, 1.0);
                     }
                 }
                 v
diff --git a/crates/io/src/pixels.rs b/crates/io/src/pixels.rs
index 1a3b1a52..3f6a6381 100644
--- a/crates/io/src/pixels.rs
+++ b/crates/io/src/pixels.rs
@@ -139,8 +139,9 @@ pub fn matte(c: f32, a: f32, white: f32) -> f32 {
 }
 
 /// Inverse of [`matte`] (returns `white` where alpha is 0).
+/// Keep HDR and negative samples; integer encoders own normalized-range clipping.
 pub fn unmatte(m: f32, a: f32, white: f32) -> f32 {
-    if a <= 0.0 { white } else { ((m - white * (1.0 - a)) / a).clamp(0.0, 1.0) }
+    if a <= 0.0 { white } else { (m - white * (1.0 - a)) / a }
 }
 
 /// `items.map(f)` on scoped threads (one per item; callers pass a handful of channels or
diff --git a/crates/io/tests/psd_structure.rs b/crates/io/tests/psd_structure.rs
index 1bf2909c..f072a06b 100644
--- a/crates/io/tests/psd_structure.rs
+++ b/crates/io/tests/psd_structure.rs
@@ -418,6 +418,15 @@ fn merged_composite_unmattes_photoshop_white() {
     let (d, _) = psd_to_document(&f);
     let p = d.layers[0].surface().unwrap().pixel(0, 0);
     assert!(p[1] < 0.01 && (p[3] - 128.0 / 255.0).abs() < 1e-6, "{p:?}");
+
+    // HDR and negative straight samples must survive the actual F32 PSD import boundary.
+    let mut hdr = testgen::merged_only(Version::Psd, ColorMode::Rgb, 32, Compression::Raw, 1, 1);
+    hdr.header.channels = 4;
+    hdr.image_data =
+        photocraft_psd::ImageData { compression: Compression::Raw, data: [1.5_f32, 0.25, 0.5, 0.5].into_iter().flat_map(f32::to_be_bytes).collect() };
+    let imported = import("hdr.psd", &hdr.to_bytes().unwrap()).unwrap().document;
+    assert_eq!(imported.depth, photocraft_color::SampleType::F32);
+    assert_eq!(imported.layers[0].surface().unwrap().pixel(0, 0), vec![2.0, -0.5, 0.0, 0.5]);
 }
 
 #[test]