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Remove Background: distance mode finds the nearest color before converting

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In distance mode, each pixel took a square root for every background color.
The nearest color is now found by squared distance, and only that distance is
converted to a percentage. The levels do not change.
This commit is contained in:
dotCooCoo
2026-11-11 21:24:45 -08:00
parent 6d6bbff53b
commit 0ef33f6e41
1 changed files with 16 additions and 10 deletions
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crates/engine/src/cmd/addons/image.rs
+16 -10
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@@ -520,7 +520,7 @@ pub(crate) fn levels(w: usize, h: usize, px: &dyn Fn(usize) -> [u16; 4], setting
/// the tolerance plus the softness on, and in proportion between them.
fn level(c: [u16; 3], refs: &[[u16; 3]], settings: &Settings) -> u8 {
let Settings { tolerance, softness, measure, .. } = *settings;
let d = refs.iter().map(|r| apart(c, *r, measure)).fold(f64::INFINITY, f64::min);
let d = percent(refs.iter().map(|r| gap(c, *r, measure)).fold(f64::INFINITY, f64::min), measure);
if d <= tolerance {
0
} else if d >= tolerance + softness {
@@ -530,16 +530,22 @@ fn level(c: [u16; 3], refs: &[[u16; 3]], settings: &Settings) -> u8 {
}
}
/// How far apart `a` and `b` are, as a percentage, measured as `measure` says: the RGB distance of
/// the largest one (black to white), or the largest difference on one channel of the channel's range.
/// A difference of `k` 8-bit steps on one channel is exactly `k / 255 × 100` with channels.
fn apart(a: [u16; 3], b: [u16; 3], measure: Match) -> f64 {
/// How far apart `a` and `b` are, measured as `measure` says, before `percent` converts it: the
/// squared RGB distance, or the largest difference on one channel.
fn gap(a: [u16; 3], b: [u16; 3], measure: Match) -> f64 {
match measure {
Match::Distance => {
let sq: f64 = a.iter().zip(b).map(|(x, y)| (f64::from(*x) - f64::from(y)).powi(2)).sum();
sq.sqrt() / (65_535.0 * 3f64.sqrt()) * 100.0
}
Match::Channels => f64::from(a.iter().zip(b).map(|(x, y)| x.abs_diff(y)).max().unwrap_or(0)) / 65_535.0 * 100.0,
Match::Distance => a.iter().zip(b).map(|(x, y)| (f64::from(*x) - f64::from(y)).powi(2)).sum(),
Match::Channels => f64::from(a.iter().zip(b).map(|(x, y)| x.abs_diff(y)).max().unwrap_or(0)),
}
}
/// A `gap` as a percentage: of the largest RGB distance (black to white) with distance, or of the
/// channel's range with channels. A difference of `k` 8-bit steps on one channel is exactly
/// `k / 255 × 100` with channels.
fn percent(gap: f64, measure: Match) -> f64 {
match measure {
Match::Distance => gap.sqrt() / (65_535.0 * 3f64.sqrt()) * 100.0,
Match::Channels => gap / 65_535.0 * 100.0,
}
}