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use std::collections::HashMap;
#[cfg(rand)]
use rand::{prelude::*, seq::index::sample};
use rgb::{RGB, RGB8};
pub struct KMeans {
samples: Vec<RGB8>,
}
#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
struct HashableRGBF {
inner: (u32, u32, u32),
}
impl From<RGB<f32>> for HashableRGBF {
fn from(value: RGB<f32>) -> Self {
Self {
inner: (value.r.to_bits(), value.g.to_bits(), value.b.to_bits()),
}
}
}
impl KMeans {
pub fn new(samples: Vec<RGB8>) -> Self {
Self { samples }
}
pub fn get_k_colors(&self, k: usize, max_iter: usize) -> Vec<RGB8> {
let mut centroids = self.get_centroid_seeds_simple(k);
for _ in 0..max_iter {
let mut clusters: HashMap<HashableRGBF, Vec<RGB8>> = HashMap::new();
for &sample in &self.samples {
let closest_centroid = Self::closest_centroid(¢roids, sample.into());
clusters
.entry(closest_centroid.into())
.or_default()
.push(sample);
}
centroids = clusters
.into_values()
.map(|members| vector_avg(&members))
.collect()
}
centroids
.into_iter()
.map(|c| RGB8::new(c.r.round() as u8, c.g.round() as u8, c.b.round() as u8))
.collect()
}
/// Picks a point at random (if feature rand is enabled) for the first centroid, then iteratively adds the point furthest away from any centroid
/// A more complex solution is the probabilistic k-means++ algorithm (https://www.mathworks.com/help/stats/kmeans.html#bueq7aj-5)
fn get_centroid_seeds_simple(&self, k: usize) -> Vec<RGB<f32>> {
if k >= self.samples.len() {
return self.samples.iter().map(|&v| v.into()).collect();
}
#[cfg(rand)]
let index = thread_rng().gen_range(0..self.samples.len());
#[cfg(not(rand))]
let index = 0; //lol
let mut centroids: Vec<RGB<f32>> = vec![self.samples[index].into()];
while centroids.len() < k {
let next = *self
.samples
.iter()
.max_by(|&&v1, &&v2| {
let v1_closest_centroid = Self::closest_centroid(¢roids, v1.into());
let v2_closest_centroid = Self::closest_centroid(¢roids, v2.into());
vector_diff_2_norm(v1.into(), v1_closest_centroid)
.partial_cmp(&vector_diff_2_norm(v2.into(), v2_closest_centroid))
.unwrap()
})
.unwrap();
centroids.push(next.into());
}
centroids
}
fn closest_centroid(centroids: &[RGB<f32>], v: RGB<f32>) -> RGB<f32> {
*centroids
.iter()
.min_by(|&&c1, &&c2| {
vector_diff_2_norm(c1, v)
.partial_cmp(&vector_diff_2_norm(c2, v))
.unwrap()
})
.unwrap()
}
#[cfg(rand)]
fn get_centroid_seeds_random(&self, k: usize) -> Vec<RGB<f32>> {
if k >= self.samples.len() {
return self.samples.iter().map(|&v| v.into()).collect();
}
sample(&mut thread_rng(), self.samples.len(), k)
.into_iter()
.map(|i| self.samples[i].into())
.collect()
}
}
fn vector_diff(v1: RGB<f32>, v2: RGB<f32>) -> RGB<f32> {
RGB::new(v1.r - v2.r, v1.g - v2.g, v1.b - v2.b)
}
fn vector_diff_2_norm(v1: RGB<f32>, v2: RGB<f32>) -> f32 {
let diff = vector_diff(v1, v2);
(diff.r.powi(2) + diff.g.powi(2) + diff.b.powi(2)).sqrt()
}
fn vector_sum(acc: RGB<f32>, elem: RGB<f32>) -> RGB<f32> {
RGB::new(acc.r + elem.r, acc.g + elem.g, acc.b + elem.b)
}
fn vector_avg(vs: &[RGB8]) -> RGB<f32> {
let summed = vs.iter().fold(RGB::new(0.0, 0.0, 0.0), |acc, elem| {
vector_sum(acc, (*elem).into())
});
RGB::new(
summed.r / vs.len() as f32,
summed.g / vs.len() as f32,
summed.b / vs.len() as f32,
)
}
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