From e82b5089f7dc50bafb911930360041307f139413 Mon Sep 17 00:00:00 2001
From: radialmonster <radial@gmail.com>
Date: Tue, 13 Oct 2026 02:36:28 -0400
Subject: [PATCH] LR-RAW-DNG: DNGs written by older LightCraft keep their
 sensor-anchored CFAPattern reading; the writer now marks its spec-anchored
 files 'LightCraft DNG 2'

---
 crates/raw/src/dng.rs      |  6 +++++-
 crates/raw/src/dngwrite.rs |  6 +++++-
 crates/raw/tests/dng.rs    | 18 ++++++++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/crates/raw/src/dng.rs b/crates/raw/src/dng.rs
index 3c7ece61b..b75f4c61a 100644
--- a/crates/raw/src/dng.rs
+++ b/crates/raw/src/dng.rs
@@ -303,7 +303,11 @@ pub(crate) fn decode_as(bytes: &[u8], mode: Mode, format: RawFormat) -> Result<R
         }
         // the tag is anchored at the top-left of the ActiveArea (DNG spec); `RawImage::cfa` is anchored at the
         // sensor origin (the crop to the active area shifts it back), so move the anchor out by the area's offset
-        Some(Cfa { width: cols, height: rows, pattern }.shifted(cols - active_area.x % cols, rows - active_area.y % rows))
+        // (LightCraft's own DNGs from before the writer followed the spec carry the sensor-origin pattern; they are marked by
+        // a bare "LightCraft" Software tag, the writer now says [`crate::dngwrite::SOFTWARE`], and keep their original reading)
+        let at_origin = Cfa { width: cols, height: rows, pattern };
+        let legacy_writer = [raw, ifd0].iter().any(|i| i.string(t::SOFTWARE).as_deref().map(str::trim) == Some("LightCraft"));
+        Some(if legacy_writer { at_origin } else { at_origin.shifted(cols - active_area.x % cols, rows - active_area.y % rows) })
     } else {
         None
     };
diff --git a/crates/raw/src/dngwrite.rs b/crates/raw/src/dngwrite.rs
index 55a96984b..10e032c69 100644
--- a/crates/raw/src/dngwrite.rs
+++ b/crates/raw/src/dngwrite.rs
@@ -25,6 +25,10 @@ pub enum DngCompression {
     },
 }
 
+/// Software tag of the DNGs this writer makes. A bare "LightCraft" marks older files, whose CFAPattern is anchored at
+/// the sensor origin instead of the ActiveArea (the reader keeps their original reading).
+pub const SOFTWARE: &str = "LightCraft DNG 2";
+
 /// IEEE 754 binary32 → binary16 (round to nearest even; overflow → ±inf, NaN kept).
 pub fn f32_to_f16(v: f32) -> u16 {
     let b = v.to_bits();
@@ -119,7 +123,7 @@ pub fn write_dng(raw: &RawImage, opts: &DngWriteOptions) -> Result<Vec<u8>> {
     let unique = format!("{make} {model}").trim().to_string();
     ifd.set(t::UNIQUE_CAMERA_MODEL, Value::Ascii(if unique.is_empty() { "LightCraft".into() } else { unique }));
     ifd.set(t::ORIENTATION, Value::Short(vec![raw.orientation.to_exif()]));
-    ifd.set(t::SOFTWARE, Value::Ascii("LightCraft".into()));
+    ifd.set(t::SOFTWARE, Value::Ascii(SOFTWARE.into()));
     let xmp = opts.xmp.clone().unwrap_or_else(|| lightcraft_meta::write_xmp(&raw.metadata, None));
     ifd.set(t::XMP, Value::Byte(xmp.into_bytes()));
 
diff --git a/crates/raw/tests/dng.rs b/crates/raw/tests/dng.rs
index 9876e349e..a26a4375c 100644
--- a/crates/raw/tests/dng.rs
+++ b/crates/raw/tests/dng.rs
@@ -1047,3 +1047,21 @@ fn cfa_pattern_is_relative_to_the_active_area() {
         assert_eq!(back.normalized().unwrap().cfa.unwrap().name(), "GRBG");
     }
 }
+
+/// DNGs LightCraft wrote before the writer anchored the pattern at the ActiveArea carry a bare "LightCraft" Software
+/// tag and a sensor-origin pattern; they keep that reading, while the current writer marks its files differently.
+#[test]
+fn legacy_lightcraft_dng_keeps_the_sensor_anchored_pattern() {
+    let (w, h) = (20, 12);
+    let build = |software: &str| {
+        let mut raw = base_ifd(w, h, 16, 1, true);
+        raw.set_image(ImageData::Strips { rows_per_strip: h as u32, strips: vec![u16_bytes(&pattern(w, h, 1, 16), ByteOrder::Little)] });
+        raw.set(t::WHITE_LEVEL, Value::Short(vec![65535]));
+        raw.set(t::ACTIVE_AREA, Value::Long(vec![1, 0, h as u32 - 1, w as u32 - 1]));
+        raw.set(t::SOFTWARE, Value::Ascii(software.into()));
+        decode(&dng(raw, ByteOrder::Little)).unwrap()
+    };
+    assert_eq!(build("LightCraft").cfa.unwrap().name(), "GRBG");
+    assert_eq!(build("Adobe Photoshop Lightroom").cfa.unwrap().name(), "BGGR");
+    assert_ne!(lightcraft_raw::dngwrite::SOFTWARE, "LightCraft");
+}