Merge pull request #235 from Gremiger/fix/issue-212-nef-dng-white-balance

Issue #212: Raw: keep vendor white balance when writing DNG

crates/raw/src/dngwrite.rs

@@ -177,6 +177,9 @@ pub fn write_dng(raw: &RawImage, opts: &DngWriteOptions) -> Result<Vec<u8>> {
         ifd.set(t::AS_SHOT_NEUTRAL, rat_vec(&v));
     } else if let Some(xy) = c.as_shot_white_xy {
         ifd.set(t::AS_SHOT_WHITE_XY, rat_vec(&[xy.x, xy.y]));
+    } else if let Some(m) = raw.wb_multipliers.filter(|m| m.iter().all(|v| *v > 0.0 && v.is_finite())) {
+        // vendor raws (NEF, ARW…) carry white balance as multipliers: the DNG neutral is their reciprocal
+        ifd.set(t::AS_SHOT_NEUTRAL, rat_vec(&m.map(|v| 1.0 / v as f64)));
     }
     ifd.set(t::BASELINE_EXPOSURE, Value::SRational(vec![srational(c.baseline_exposure)]));
     // the source's own profile look travels with its data (conversions, smart previews, merges)

crates/raw/tests/dng.rs

@@ -453,6 +453,22 @@ fn colour_transform_from_decoded_dng() {
     assert!(o.iter().all(|v| (v - 1.0).abs() < 1e-9));
 }
 
+/// Issue #212: a NEF converted to DNG came out dark and green. NEF white balance is vendor multipliers
+/// (no colour matrix, no `AsShotNeutral`); the DNG must carry them as its as-shot neutral.
+#[test]
+fn vendor_white_balance_survives_dng_conversion() {
+    let mut raw = synthetic(16, 16, Some(Cfa::bayer("RGGB").unwrap()), 1);
+    raw.color = ColorData::default();
+    raw.wb_multipliers = Some([2.25, 1.0, 1.7421875]);
+    let before = lightcraft_raw::color::camera_transform(&raw, lightcraft_raw::color::as_shot_white_xy(&raw));
+    let back = decode(&write_dng(&raw, &DngWriteOptions::default()).unwrap()).unwrap();
+    let after = lightcraft_raw::color::camera_transform(&back, lightcraft_raw::color::as_shot_white_xy(&back));
+    for c in 0..3 {
+        assert!((before.wb[c] - after.wb[c]).abs() < 1e-3, "{:?} vs {:?}", before.wb, after.wb);
+    }
+    assert!((after.wb[0] - 2.25).abs() < 1e-3 && (after.wb[2] - 1.7421875).abs() < 1e-3, "{:?}", after.wb);
+}
+
 #[test]
 fn rejects_unsupported_and_broken() {
     let (w, h) = (8, 8);