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LR-IMP-FORMATS: drop the 40D luma floor from Canon sRAW decoding 

The 512 floor and its ColorDataVersion 3 keying rested on one file.
Versions without a known black-level position now fall back to black 0
for the white level, so the 40D sRAW renders with slightly raised blacks.
This commit is contained in:
radialmonster 2026-10-09 04:18:46 -04:00
parent 1206d3fd52
commit 3af7a0c0ae
1 changed files with 19 additions and 24 deletions
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43
crates/raw/src/vendor/cr2/sraw.rs vendored
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@ -316,7 +316,6 @@ fn chroma_gains(planes: &Planes, preview: &Preview, active: Rect) -> Option<(f64
/// (word 0), located by searching the CC0 samples for the values ExifTool reports.
fn average_black_at(version: i16) -> Option<usize> {
Some(match version {
3 => 163,
6 | 7 | 9 => 231,
10 | 11 => 276,
12 | 13 | 15 => 326,
@ -324,17 +323,13 @@ fn average_black_at(version: i16) -> Option<usize> {
})
}
/// The sensor's black level in raw counts and the black pedestal carried by the luma samples, from `ColorData`.
/// The pedestal is 0 on every sample but the 40D's (`ColorDataVersion` 3), whose luma floor is 512 in the file (the
/// darkest pixels read 524–544, and the maker note repeats 512 in words 663–673).
fn colour_data_levels(words: &[u64]) -> (Option<f32>, f32) {
let version = words.first().map_or(0, |&v| v as u16 as i16);
let pedestal = if version == 3 { 512.0 } else { 0.0 };
let black = average_black_at(version).and_then(|at| words.get(at..at + 4)).and_then(|q| {
let (lo, hi) = (q.iter().min()?, q.iter().max()?);
((256..=4096).contains(lo) && hi - lo <= 8).then(|| q.iter().sum::<u64>() as f32 / 4.0)
});
(black, pedestal)
/// The sensor's black level in raw counts from `ColorData` (`None` for versions whose position is not known, and
/// when the four values are not plausible and near-equal).
fn colour_data_black(words: &[u64]) -> Option<f32> {
let version = words.first().map(|&v| v as u16 as i16)?;
let q = words.get(average_black_at(version)?..)?.get(..4)?;
let (lo, hi) = (q.iter().min()?, q.iter().max()?);
((256..=4096).contains(lo) && hi - lo <= 8).then(|| q.iter().sum::<u64>() as f32 / 4.0)
}
/// Decode a Canon sRAW / mRAW CR2 into linear white-balanced camera RGB (`cpp` 3).
@ -360,9 +355,9 @@ pub(super) fn decode(bytes: &[u8], tiff: &Tiff, raw: &Ifd, mode: Mode) -> Result
}
}
let colour_data = mn.as_ref().and_then(|m| m.ifd.value(COLOR_BALANCE).map(|v| words(v, m.order)));
let (black_counts, pedestal) = colour_data.as_deref().map_or((None, 0.0), colour_data_levels);
let black_counts = colour_data.as_deref().and_then(colour_data_black);
// 1.0 = a CFA CR2 of the same body at full 14-bit scale; see LUMA_GAIN
let white = pedestal + LUMA_GAIN * (SENSOR_FULL - black_counts.unwrap_or(0.0));
let white = LUMA_GAIN * (SENSOR_FULL - black_counts.unwrap_or(0.0));
let data = match mode {
Mode::Header => Vec::new(),
@ -387,7 +382,7 @@ pub(super) fn decode(bytes: &[u8], tiff: &Tiff, raw: &Ifd, mode: Mode) -> Result
data: RawData::U16(data),
cfa: None,
bits: 14,
black: BlackLevel::uniform(pedestal),
black: BlackLevel::uniform(0.0),
white: vec![white],
active_area: active,
crop: Rect::new(0, 0, active.width, active.height),
@ -559,22 +554,22 @@ mod tests {
}
#[test]
fn colour_data_levels_by_version() {
fn colour_data_black_by_version() {
let mut w = vec![0u64; 400];
w[0] = 7;
w[231..235].copy_from_slice(&[2048, 2047, 2048, 2048]);
assert_eq!(colour_data_levels(&w), (Some(2047.75), 0.0));
assert_eq!(colour_data_black(&w), Some(2047.75));
w[0] = 12;
assert_eq!(colour_data_levels(&w).0, None); // the black level of another version lives elsewhere
assert_eq!(colour_data_black(&w), None); // the black level of another version lives elsewhere
w[326..330].copy_from_slice(&[512, 512, 511, 512]);
assert_eq!(colour_data_levels(&w).0, Some(511.75));
assert_eq!(colour_data_black(&w), Some(511.75));
w[326..330].copy_from_slice(&[512, 512, 100, 512]); // implausible
assert_eq!(colour_data_levels(&w).0, None);
assert_eq!(colour_data_black(&w), None);
w[0] = 3;
assert_eq!(colour_data_levels(&w).1, 512.0); // the 40D's luma floor
assert_eq!(colour_data_black(&w), None); // no position known: black 0
w[0] = 65533; // -3
assert_eq!(colour_data_levels(&w), (None, 0.0));
assert_eq!(colour_data_levels(&[]), (None, 0.0));
assert_eq!(colour_data_levels(&[7, 1, 2]), (None, 0.0));
assert_eq!(colour_data_black(&w), None);
assert_eq!(colour_data_black(&[]), None);
assert_eq!(colour_data_black(&[7, 1, 2]), None);
}
}