Quantization node (#887)

Add basic quantization node

node-graph/gstd/src/quantization.rs

@@ -0,0 +1,54 @@
+use graphene_core::raster::{Color, Image};
+use graphene_core::Node;
+
+/// The `GenerateQuantizationNode` encodes the brightness of each channel of the image as an integer number
+/// sepified by the samples parameter. This node is used to asses the loss of visual information when
+/// quantizing the image using different fit functions.
+pub struct GenerateQuantizationNode<N: Node<(), Output = u32>, M: Node<(), Output = u32>> {
+	samples: N,
+	function: M,
+}
+
+#[node_macro::node_fn(GenerateQuantizationNode)]
+fn generate_quantization_fn(image: Image, samples: u32, function: u32) -> Image {
+	// Scale the input image, this can be removed by adding an extra parameter to the fit function.
+	let max_energy = 16380.;
+	let data: Vec<f64> = image.data.iter().flat_map(|x| vec![x.r() as f64, x.g() as f64, x.b() as f64]).collect();
+	let data: Vec<f64> = data.iter().map(|x| x * max_energy).collect();
+	let mut dist = autoquant::integrate_distribution(data);
+	autoquant::drop_duplicates(&mut dist);
+	let dist = autoquant::normalize_distribution(dist.as_slice());
+	let max = dist.last().unwrap().0;
+	let linear = Box::new(autoquant::SimpleFitFn {
+		function: move |x| x / max,
+		inverse: move |x| x * max,
+		name: "identity",
+	});
+	let best = match function {
+		0 => linear as Box<dyn autoquant::FitFn>,
+		1 => linear as Box<dyn autoquant::FitFn>,
+		2 => Box::new(autoquant::models::OptimizedLog::new(dist, 20)) as Box<dyn autoquant::FitFn>,
+		_ => linear as Box<dyn autoquant::FitFn>,
+	};
+
+	let roundtrip = |sample: f32| -> f32 {
+		let encoded = autoquant::encode(sample as f64 * max_energy, best.as_ref(), samples);
+		let decoded = autoquant::decode(encoded, best.as_ref(), samples) / max_energy;
+		log::trace!("{} enc: {} dec: {}", sample, encoded, decoded);
+		decoded as f32
+	};
+
+	let new_data = image
+		.data
+		.iter()
+		.map(|c| {
+			let r = roundtrip(c.r());
+			let g = roundtrip(c.g());
+			let b = roundtrip(c.b());
+			let a = c.a();
+
+			Color::from_rgbaf32_unchecked(r, g, b, a)
+		})
+		.collect();
+	Image { data: new_data, ..image }
+}