diff --git a/crates/color/src/icc.rs b/crates/color/src/icc.rs index 184c94c28..c456b025f 100644 --- a/crates/color/src/icc.rs +++ b/crates/color/src/icc.rs @@ -325,6 +325,9 @@ pub struct Clut { pub data: Vec, } +/// Most interpolating inputs [`Clut::eval`] combines (ICC allows 15). +pub const MAX_CLUT_INPUTS: usize = 16; + impl Clut { /// Multilinear interpolation at `x` (0..1 per input). pub fn eval(&self, x: &[f64]) -> Vec { @@ -347,11 +350,18 @@ impl Clut { base += k * stride[i]; } let mut out = vec![0.0; self.outputs]; - for corner in 0..(1usize << n) { + // Only the axes that interpolate have two corners: a singleton axis, or one sampled on a + // grid point, contributes its lower corner alone. ICC tables have at most 15 inputs; a + // table built with more interpolating axes than that evaluates to zero. + let active: Vec = (0..n).filter(|&i| step[i] != 0 && frac[i] != 0.0).collect(); + if active.len() > MAX_CLUT_INPUTS { + return out; + } + for corner in 0..(1usize << active.len()) { let mut w = 1.0; let mut off = base; - for i in 0..n { - if corner >> i & 1 == 1 { + for (bit, &i) in active.iter().enumerate() { + if corner >> bit & 1 == 1 { w *= frac[i]; off += step[i]; } else { @@ -1052,6 +1062,22 @@ mod tests { assert!(matches!(parse_profile(&write_matrix_profile("m", P709, D65, 2.2)).unwrap(), Profile::Matrix(_))); } + #[test] + fn clut_corners_count_only_interpolating_axes() { + // 64 singleton axes and one interpolating one: two corners, not 2^65. + let mut grid = vec![1; 64]; + grid.push(2); + let c = Clut { grid, outputs: 1, data: vec![0.0, 1.0] }; + let mut x = vec![0.5; 64]; + x.push(0.25); + assert!((c.eval(&x)[0] - 0.25).abs() < 1e-9); + // On grid points nothing interpolates. + let c = Clut { grid: vec![2; 40], outputs: 1, data: vec![] }; + assert_eq!(c.eval(&[1.0; 40]), vec![0.0]); + // More interpolating axes than ICC allows: zero, at once. + assert_eq!(c.eval(&[0.5; 40]), vec![0.0]); + } + #[test] fn clut_and_lut3d_interpolate() { // A 2-point identity CLUT on 3 inputs is exact for every point.