yuv: Add YUV420p (planar) support

Signed-off-by: Christopher N. Hesse <raymanfx@gmail.com>

ffimage-yuv/benches/convert.rs

@@ -4,7 +4,7 @@ use ffimage::{
     color::Rgb,
     iter::{ColorConvertExt, PixelsExt, WriteExt},
 };
-use ffimage_yuv::{yuv::Yuv, yuv422::Yuv422};
+use ffimage_yuv::{yuv::Yuv, yuv420::Yuv420p, yuv422::Yuv422};
 
 pub fn yuv_to_rgb(c: &mut Criterion) {
     let resolutions = [(640, 480), (1280, 720)];
@@ -51,4 +51,25 @@ pub fn yuv422_to_rgb(c: &mut Criterion) {
     }
 }
 
-criterion_group!(benches, yuv_to_rgb, yuv422_to_rgb);
+pub fn yuv420p_to_rgb(c: &mut Criterion) {
+    let resolutions = [(640, 480), (1280, 720)];
+
+    for res in resolutions {
+        let yuv420p = vec![10; ((res.0 * res.1) as f32 * 1.5) as usize];
+        let mut rgb = vec![10; res.0 * res.1 * 3];
+
+        c.bench_function(
+            &format!("Yuv420p[u8] -> Rgb[u8] ({}x{})", res.0, res.1),
+            |b| {
+                b.iter(|| {
+                    Yuv420p::pack(&yuv420p)
+                        .into_iter()
+                        .colorconvert::<Rgb<u8>>()
+                        .write(black_box(&mut rgb));
+                })
+            },
+        );
+    }
+}
+
+criterion_group!(benches, yuv_to_rgb, yuv422_to_rgb, yuv420p_to_rgb);

ffimage-yuv/src/lib.rs

@@ -1,4 +1,5 @@
 #![no_std]
 
 pub mod yuv;
+pub mod yuv420;
 pub mod yuv422;

ffimage-yuv/src/yuv420.rs

@@ -0,0 +1,57 @@
+use crate::yuv::Yuv;
+
+/// YUV 4:2:0 (Planar)
+///
+/// This is a zero-sized struct, providing useful functions for handling planar YUV images.
+/// The planar format is often used for video encoding / decoding usecases. Most cameras which
+/// output YUV image frames will usually use a packet format, e.g. YUYV aka Y422.
+pub struct Yuv420p;
+
+impl Yuv420p {
+    pub fn pack<'a, T>(buf: &'a [T]) -> impl IntoIterator<Item = Yuv<T>> + 'a
+    where
+        T: Copy,
+    {
+        // buf must have a rectangular shape
+        assert_eq!(buf.len() % 2, 0);
+        // buf must be divisible in 3 parts: 2/3 Luma (y) samples, 1/3 Chroma (u + v) samples
+        assert_eq!(buf.len() % 3, 0);
+
+        let pixels = (buf.len() / 3) * 2;
+        let width = pixels / 4;
+
+        let y = &buf[0..pixels];
+        let u = &buf[pixels..(pixels + width)];
+        let v = &buf[(pixels + width)..(pixels + width * 2)];
+
+        Yuv420p::pack_planes(y, u, v)
+    }
+
+    pub fn pack_planes<'a, T>(
+        y: &'a [T],
+        u: &'a [T],
+        v: &'a [T],
+    ) -> impl IntoIterator<Item = Yuv<T>> + 'a
+    where
+        T: Copy,
+    {
+        // YUV420 has 2x2 blocks of Luma (y) samples
+        assert_eq!(y.len() % 4, 0);
+        let width = y.len() / 4;
+        let height = y.len() / width;
+        assert_eq!(u.len(), width);
+        assert_eq!(v.len(), width);
+
+        (0..height)
+            .into_iter()
+            .zip((0..width).into_iter())
+            .map(move |(i, j)| {
+                let y_idx = i * width + j;
+                let uv_idx = i / 2 * width / 2 + j / 2;
+                let y = y[y_idx];
+                let u = u[uv_idx];
+                let v = v[uv_idx];
+                Yuv([y, u, v])
+            })
+    }
+}