Add Rec. 709 and Rec. 2020

palette/src/encoding.rs

@@ -7,10 +7,12 @@
 
 pub use self::gamma::{F2p2, Gamma};
 pub use self::linear::Linear;
+pub use self::rec_standards::{Rec2020, Rec709};
 pub use self::srgb::Srgb;
 
 pub mod gamma;
 pub mod linear;
+pub mod rec_standards;
 pub mod srgb;
 
 /// A transfer function from linear space.

palette/src/encoding/rec_standards.rs

@@ -0,0 +1,296 @@
+//! The ITU-R Recommendation BT.2020 (Rec. 2020) and BT.709 (Rec. 709) standards and their
+//! associated transfer function.
+
+use crate::{
+    bool_mask::LazySelect,
+    encoding::{FromLinear, IntoLinear, Srgb},
+    luma::LumaStandard,
+    num::{Arithmetics, MulAdd, MulSub, PartialCmp, Powf, Real},
+    rgb::{Primaries, RgbSpace, RgbStandard},
+    white_point::{Any, D65},
+    Mat3, Yxy,
+};
+
+use lookup_tables::*;
+
+mod lookup_tables;
+
+/// The Rec. 2020 standard, color space, and transfer function.
+///
+/// # As transfer function
+///
+/// `Rec2020` will not use any kind of approximation when converting from `T` to
+/// `T`. This involves calls to `powf`, which may make it too slow for certain
+/// applications.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct Rec2020;
+
+impl<T: Real> Primaries<T> for Rec2020 {
+    // Primary values taken from ITU specification:
+    // https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.2020-2-201510-I!!PDF-E.pdf
+    fn red() -> Yxy<Any, T> {
+        Yxy::new(T::from_f64(0.708), T::from_f64(0.292), T::from_f64(0.2627))
+    }
+    fn green() -> Yxy<Any, T> {
+        Yxy::new(T::from_f64(0.170), T::from_f64(0.797), T::from_f64(0.6780))
+    }
+    fn blue() -> Yxy<Any, T> {
+        Yxy::new(T::from_f64(0.131), T::from_f64(0.046), T::from_f64(0.0593))
+    }
+}
+
+impl RgbSpace for Rec2020 {
+    type Primaries = Rec2020;
+    type WhitePoint = D65;
+
+    #[rustfmt::skip]
+    #[inline(always)]
+    fn rgb_to_xyz_matrix() -> Option<Mat3<f64>> {
+        // Matrix calculated using specified primary values and white point
+        // using formulas from http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
+        Some([
+            0.6370102, 0.1446150, 0.1688448,
+            0.2627217, 0.6779893, 0.0592890,
+            0.0000000, 0.0280723, 1.0607577,
+        ])
+    }
+
+    #[rustfmt::skip]
+    #[inline(always)]
+    fn xyz_to_rgb_matrix() -> Option<Mat3<f64>> {
+        // Matrix calculated using specified primary values and white point
+        // using formulas from http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
+        Some([
+             1.7165107, -0.3556417, -0.2533455,
+            -0.6666930,  1.6165022,  0.0157688,
+             0.0176436, -0.0427798,  0.9423051,
+        ])
+    }
+}
+
+impl RgbStandard for Rec2020 {
+    type Space = Rec2020;
+    type TransferFn = RecOetf;
+}
+
+impl LumaStandard for Rec2020 {
+    type WhitePoint = D65;
+    type TransferFn = RecOetf;
+}
+
+/// The Rec. 709 standard, color space, and transfer function.
+///
+/// # As transfer function
+///
+/// `Rec709` will not use any kind of approximation when converting from `T` to
+/// `T`. This involves calls to `powf`, which may make it too slow for certain
+/// applications.
+pub struct Rec709;
+
+impl RgbStandard for Rec709 {
+    type Space = Srgb;
+    type TransferFn = RecOetf;
+}
+
+impl LumaStandard for Rec709 {
+    type WhitePoint = D65;
+    type TransferFn = RecOetf;
+}
+
+/// The opto-electronic transfer function used in standard dynamic range (SDR)
+/// standards by the ITU-R such as [`Rec709`] and [`Rec2020`].
+pub struct RecOetf;
+
+const ALPHA: f64 = 1.09929682680944;
+const BETA: f64 = 0.018053968510807;
+
+impl<T> IntoLinear<T, T> for RecOetf
+where
+    T: Real + Powf + MulAdd + Arithmetics + PartialCmp + Clone,
+    T::Mask: LazySelect<T>,
+{
+    #[inline]
+    fn into_linear(encoded: T) -> T {
+        lazy_select! {
+            if encoded.lt(&T::from_f64(4.5*BETA)) => T::from_f64(1.0 / 4.5) * &encoded,
+            else => encoded.clone().mul_add(T::from_f64(1.0 / ALPHA), T::from_f64(1.0 - 1.0 / ALPHA)).powf(T::from_f64(1.0 / 0.45))
+        }
+    }
+}
+
+impl<T> FromLinear<T, T> for RecOetf
+where
+    T: Real + Powf + MulSub + Arithmetics + PartialCmp + Clone,
+    T::Mask: LazySelect<T>,
+{
+    #[inline]
+    fn from_linear(linear: T) -> T {
+        lazy_select! {
+            if linear.lt(&T::from_f64(BETA)) => T::from_f64(4.5) * &linear,
+            else => linear.clone().powf(T::from_f64(0.45)).mul_sub(T::from_f64(ALPHA), T::from_f64(ALPHA - 1.0))
+        }
+    }
+}
+
+impl IntoLinear<f32, u8> for RecOetf {
+    #[inline]
+    fn into_linear(encoded: u8) -> f32 {
+        REC_OETF_U8_TO_F32[encoded as usize]
+    }
+}
+
+impl FromLinear<f32, u8> for RecOetf {
+    #[inline]
+    fn from_linear(linear: f32) -> u8 {
+        // Algorithm modeled closely off of `f32_to_srgb8` from fast-srgb8 crate
+        const MAX_FLOAT_BITS: u32 = 0x3f7fffff; // 1.0 - f32::EPSILON
+        const MIN_FLOAT_BITS: u32 = 0x39000000; // 2^(-13)
+        let max_float = f32::from_bits(MAX_FLOAT_BITS);
+        let min_float = f32::from_bits(MIN_FLOAT_BITS);
+
+        let mut input = linear;
+        // Implemented this way to map NaN to `min_float`
+        if input.partial_cmp(&min_float) != Some(core::cmp::Ordering::Greater) {
+            input = min_float;
+        } else if input > max_float {
+            input = max_float;
+        }
+        let input_bits = input.to_bits();
+        #[cfg(test)]
+        {
+            debug_assert!((MIN_FLOAT_BITS..=MAX_FLOAT_BITS).contains(&input_bits));
+        }
+        // Safety: all input floats are clamped into the {min_float, max_float} range,
+        // which turns out in this case to guarantee that their bitwise reprs are
+        // clamped to the {MIN_FLOAT_BITS, MAX_FLOAT_BITS} range (guaranteed by the
+        // fact that min_float/max_float are the normal, finite, the same sign, and
+        // not zero).
+        //
+        // Because of that, the smallest result of `input_bits - MIN_FLOAT_BITS` is 0
+        // (when `input_bits` is `MIN_FLOAT_BITS`), and the largest is `0x067fffff`,
+        // (when `input_bits` is `MAX_FLOAT_BITS`). `0x067fffff >> 20` is 0x67, e.g. 103,
+        // and thus all possible results are inbounds for the (104 item) table.
+        // This is all verified in test code.
+        //
+        // Note that the compiler can't figure this out on it's own, so the
+        // get_unchecked does help some.
+        let entry = {
+            let i = ((input_bits - MIN_FLOAT_BITS) >> 20) as usize;
+            #[cfg(all(not(bench), test))]
+            {
+                debug_assert!(TO_REC_OETF_U8.get(i).is_some());
+            }
+            unsafe { *TO_REC_OETF_U8.get_unchecked(i) }
+        };
+
+        let bias = (entry >> 16) << 9;
+        let scale = entry & 0xffff;
+
+        let t = (input_bits >> 12) & 0xff;
+        let res = (bias + scale * t) >> 16;
+        #[cfg(test)]
+        {
+            debug_assert!(res < 256, "{}", res);
+        }
+        res as u8
+    }
+}
+
+impl IntoLinear<f64, u8> for RecOetf {
+    #[inline]
+    fn into_linear(encoded: u8) -> f64 {
+        REC_OETF_U8_TO_F64[encoded as usize]
+    }
+}
+
+impl FromLinear<f64, u8> for RecOetf {
+    #[inline]
+    fn from_linear(linear: f64) -> u8 {
+        RecOetf::from_linear(linear as f32)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    #[cfg(feature = "approx")]
+    mod conversion {
+        use crate::{
+            encoding::Rec2020,
+            matrix::{matrix_inverse, rgb_to_xyz_matrix},
+            rgb::RgbSpace,
+        };
+
+        #[test]
+        fn rgb_to_xyz() {
+            let dynamic = rgb_to_xyz_matrix::<Rec2020, f64>();
+            let constant = Rec2020::rgb_to_xyz_matrix().unwrap();
+            assert_relative_eq!(dynamic[..], constant[..], epsilon = 0.0000001);
+        }
+
+        #[test]
+        fn xyz_to_rgb() {
+            let dynamic = matrix_inverse(rgb_to_xyz_matrix::<Rec2020, f64>());
+            let constant = Rec2020::xyz_to_rgb_matrix().unwrap();
+            assert_relative_eq!(dynamic[..], constant[..], epsilon = 0.0000001);
+        }
+    }
+
+    #[cfg(feature = "approx")]
+    mod transfer {
+        use crate::encoding::{rec_standards::RecOetf, FromLinear, IntoLinear};
+
+        #[test]
+        fn lin_to_enc_to_lin() {
+            for i in 0..=100 {
+                let linear = i as f64 / 100.0;
+                let encoded: f64 = RecOetf::from_linear(linear);
+                assert_relative_eq!(linear, RecOetf::into_linear(encoded), epsilon = 0.0000001);
+            }
+        }
+
+        #[test]
+        fn enc_to_lin_to_enc() {
+            for i in 0..=100 {
+                let encoded = i as f64 / 100.0;
+                let linear: f64 = RecOetf::into_linear(encoded);
+                assert_relative_eq!(encoded, RecOetf::from_linear(linear), epsilon = 0.0000001);
+            }
+        }
+
+        #[test]
+        fn test_u8_f32_into_impl() {
+            for i in 0..=255u8 {
+                let u8_impl: f32 = RecOetf::into_linear(i);
+                let f32_impl = RecOetf::into_linear(i as f32 / 255.0);
+                assert_relative_eq!(u8_impl, f32_impl, epsilon = 0.0000001);
+            }
+        }
+
+        #[test]
+        fn test_u8_f64_into_impl() {
+            for i in 0..=255u8 {
+                let u8_impl: f64 = RecOetf::into_linear(i);
+                let f64_impl = RecOetf::into_linear(i as f64 / 255.0);
+                assert_relative_eq!(u8_impl, f64_impl, epsilon = 0.0000001);
+            }
+        }
+
+        #[test]
+        fn u8_to_f32_to_u8() {
+            for expected in 0u8..=255u8 {
+                let linear: f32 = RecOetf::into_linear(expected);
+                let result: u8 = RecOetf::from_linear(linear);
+                assert_eq!(result, expected);
+            }
+        }
+
+        #[test]
+        fn u8_to_f64_to_u8() {
+            for expected in 0u8..=255u8 {
+                let linear: f64 = RecOetf::into_linear(expected);
+                let result: u8 = RecOetf::from_linear(linear);
+                assert_eq!(result, expected);
+            }
+        }
+    }
+}