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File formats: JPEG 2000 prefers the display resolution box over the capture box in either order

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This commit is contained in:
dotCooCoo
2026-11-02 12:04:14 +07:00
committed by bflatastic
parent 3dad9dbbfc
commit d8d0602c64
4 changed files with 19 additions and 11 deletions
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crates/engine/src/cmd/fileio/ppi.rs
+12 -7
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@@ -40,29 +40,34 @@ fn jp2_axis(n: u16, d: u16, e: i8) -> Option<f64> {
(ppi.is_finite() && (1.0..=100_000.0).contains(&ppi)).then_some(ppi)
}
/// JP2 resolution is independent on each axis. Later capture or display boxes replace earlier
/// valid values for that axis; an invalid later axis leaves the earlier value intact.
/// JP2 resolution is independent on each axis. A valid display (`resd`) value, the resolution the
/// image is meant to be reproduced at, wins over a capture (`resc`) value whichever box comes first;
/// the capture value is used for an axis with no valid display value. Within one box type, later
/// boxes replace earlier valid values for that axis; an invalid later axis leaves the earlier value intact.
fn jp2(b: &[u8]) -> Option<(f64, f64)> {
if !b.starts_with(b"\0\0\0\x0cjP \r\n\x87\n") {
return Some((72.0, 72.0));
}
let (mut x, mut y) = (None, None);
// [capture, display], each (x, y).
let mut found = [(None, None); 2];
for (_, header) in super::jp2read::boxes(b).filter(|(ty, _)| *ty == b"jp2h") {
for (_, res) in super::jp2read::boxes(header).filter(|(ty, _)| *ty == b"res ") {
for (_, data) in super::jp2read::boxes(res).filter(|(ty, _)| *ty == b"resc" || *ty == b"resd") {
for (ty, data) in super::jp2read::boxes(res).filter(|(ty, _)| *ty == b"resc" || *ty == b"resd") {
let Some([vn0, vn1, vd0, vd1, hn0, hn1, hd0, hd1, ve, he]): Option<[u8; 10]> = data.get(..10).and_then(|v| v.try_into().ok()) else {
continue;
};
let (x, y) = &mut found[usize::from(ty == b"resd")];
if let Some(value) = jp2_axis(u16::from_be_bytes([hn0, hn1]), u16::from_be_bytes([hd0, hd1]), he as i8) {
x = Some(value);
*x = Some(value);
}
if let Some(value) = jp2_axis(u16::from_be_bytes([vn0, vn1]), u16::from_be_bytes([vd0, vd1]), ve as i8) {
y = Some(value);
*y = Some(value);
}
}
}
}
Some((x.unwrap_or(72.0), y.unwrap_or(72.0)))
let [(cx, cy), (dx, dy)] = found;
Some((dx.or(cx).unwrap_or(72.0), dy.or(cy).unwrap_or(72.0)))
}
/// `n` bytes at `at` (`None` past the end; offsets come from the file, so no overflow either).
crates/engine/src/cmd/fileio/tests_jp2read.rs
+5 -2
View File
@@ -76,7 +76,7 @@ fn signatures_and_every_extension() {
}
#[test]
fn resolution_boxes_use_last_valid_axis_and_72_fallback() {
fn resolution_boxes_prefer_display_then_last_valid_axis_and_72_fallback() {
let check = |children: &[Vec<u8>], want: (f64, f64)| {
let file = with_resolution(children);
let got = ppi::resolution(&file).unwrap();
@@ -90,7 +90,10 @@ fn resolution_boxes_use_last_valid_axis_and_72_fallback() {
check(&[res(b"resc", 30000, 30000)], (300.0, 300.0));
check(&[res(b"resd", 15000, 15000)], (150.0, 150.0));
check(&[res(b"resc", 30000, 30000), res(b"resd", 15000, 15000)], (150.0, 150.0));
check(&[res(b"resd", 15000, 15000), res(b"resc", 30000, 30000)], (300.0, 300.0));
check(&[res(b"resd", 15000, 15000), res(b"resc", 30000, 30000)], (150.0, 150.0));
check(&[res(b"resd", 30000, 15000), res(b"resc", 7500, 7500)], (150.0, 300.0));
check(&[res(b"resd", 0, 15000), res(b"resc", 30000, 30000)], (150.0, 300.0));
check(&[res(b"resc", 30000, 30000), res(b"resd", 0, 15000)], (150.0, 300.0));
check(&[res(b"resc", 30000, 15000)], (150.0, 300.0));
assert_eq!(ppi::resolution(RAW), Some((72.0, 72.0)));
assert!((ppi::resolution(PPI300).unwrap().0 - 300.0).abs() < 0.01);