cmm: add color-management module

src/cmm/cmm_luminance.rs

@@ -0,0 +1,72 @@
+use crate::{
+    cmm::cmm_transform::{ColorMatrix, Xyz},
+    utils::ordered_float::F64,
+};
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+pub struct Luminance {
+    pub min: F64,
+    pub max: F64,
+    pub white: F64,
+}
+
+impl Luminance {
+    pub const SRGB: Self = Self {
+        min: F64(0.2),
+        max: F64(80.0),
+        white: F64(80.0),
+    };
+
+    #[expect(dead_code)]
+    pub const BT1886: Self = Self {
+        min: F64(0.01),
+        max: F64(100.0),
+        white: F64(100.0),
+    };
+
+    pub const ST2084_PQ: Self = Self {
+        min: F64(0.0),
+        max: F64(10000.0),
+        white: F64(203.0),
+    };
+
+    #[expect(dead_code)]
+    pub const HLG: Self = Self {
+        min: F64(0.005),
+        max: F64(1000.0),
+        white: F64(203.0),
+    };
+
+    pub const WINDOWS_SCRGB: Self = Self {
+        min: Self::ST2084_PQ.min,
+        max: Self::ST2084_PQ.max,
+        // This causes the white balance formula (with target ST2084_PQ) to simplify to
+        // `Y * 80 / 10000`, meaning that sRGB pure white maps to a luminance of
+        // 80 cd/m^2.
+        white: F64(Self::ST2084_PQ.white.0 / 80.0 * Self::ST2084_PQ.max.0),
+    };
+}
+
+impl Default for Luminance {
+    fn default() -> Self {
+        Self::SRGB
+    }
+}
+
+#[expect(non_snake_case)]
+pub fn white_balance(from: &Luminance, to: &Luminance, w_to: (F64, F64)) -> ColorMatrix<Xyz, Xyz> {
+    let a = ((from.max - from.min) / (to.max - to.min) * (to.white - from.min)
+        / (from.white - from.min))
+        .0;
+    let d = ((from.min - to.min) / (to.max - to.min)).0.max(0.0);
+    let s = a - d;
+    let (F64(x_to), F64(y_to)) = w_to;
+    let X_to = x_to / y_to;
+    let Y_to = 1.0;
+    let Z_to = (1.0 - x_to - y_to) / y_to;
+    ColorMatrix::new([
+        [s, 0.0, 0.0, d * X_to],
+        [0.0, s, 0.0, d * Y_to],
+        [0.0, 0.0, s, d * Z_to],
+    ])
+}