356 lines
10 KiB
Rust
356 lines
10 KiB
Rust
mod base83;
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mod srgb_lookup;
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use std::f32::consts::PI;
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use srgb_lookup::srgb_to_linear;
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const BYTES_PER_PIXEL: usize = 4;
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/// How many components should be used in blurhash creation
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///
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/// More components will increase the definition of the blurhash, but also increase processing
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/// time.
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pub struct Components {
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pub x: u32,
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pub y: u32,
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}
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/// Width and height of the input image
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#[derive(Clone, Copy, Debug)]
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pub struct ImageBounds {
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pub width: u32,
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pub height: u32,
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}
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struct ComponentState {
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x: u32,
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y: u32,
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basis: f32,
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}
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/// Error raised when too many components are requested
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#[derive(Debug)]
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pub struct ComponentError;
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/// Encoder type used to produce blurhashes
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pub struct Encoder {
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index: usize,
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components: Components,
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factors: Box<[(ComponentState, [f32; BYTES_PER_PIXEL])]>,
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bounds: ImageBounds,
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}
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/// A simple "encode this image please" function
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///
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/// The input image must be in the sRGB colorspace and be formatted as 8bit RGBA
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pub fn encode(
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components: Components,
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bounds: ImageBounds,
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rgba8_image: &[u8],
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) -> Result<String, ComponentError> {
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let mut encoder = Encoder::new(components, bounds)?;
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encoder.update(rgba8_image);
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Ok(encoder.finalize())
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}
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impl Encoder {
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/// Create a new Encoder to produce a blurhash
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///
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/// Errors if too many components are requested
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pub fn new(
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Components { x, y }: Components,
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bounds: ImageBounds,
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) -> Result<Self, ComponentError> {
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if !(1..=9).contains(&x) || !(1..=9).contains(&y) {
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return Err(ComponentError);
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}
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Ok(Self {
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index: 0,
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components: Components { x, y },
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factors: Box::from(
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(0..y)
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.flat_map(|y| {
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(0..x).map(move |x| (ComponentState { x, y, basis: 0. }, [0., 0., 0., 0.]))
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})
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.collect::<Vec<_>>(),
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),
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bounds,
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})
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}
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/// Update the encoder with bytes from an image
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///
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/// The input image must be in the sRGB colorspace and be formatted as 8bit RGBA
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/// The input doesn't need to contain whole pixels, the encoder is capable of handling partial
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/// pixels
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pub fn update(&mut self, rgba8_image: &[u8]) {
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// get offset in terms of already-processed bytes
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let offset = self.index % BYTES_PER_PIXEL;
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// get offset in terms of remaining bytes on head of rgba8_image
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let offset = (BYTES_PER_PIXEL - offset) % BYTES_PER_PIXEL;
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let basis_scale_x = PI / self.bounds.width as f32;
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let basis_scale_y = PI / self.bounds.height as f32;
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for (ComponentState { basis, .. }, [_, g, b, _]) in self.factors.iter_mut() {
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for (val, slot) in rgba8_image[..offset]
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.iter()
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.map(|byte| *basis * srgb_to_linear(*byte))
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.zip(
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[b, g][..offset.saturating_sub(BYTES_PER_PIXEL - 2)]
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.iter_mut()
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.rev(),
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)
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{
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**slot += val;
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}
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}
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let pixels = ((self.index + offset) / BYTES_PER_PIXEL) as u32;
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let mut chunks = rgba8_image[offset..].chunks_exact(BYTES_PER_PIXEL);
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for (i, chunk) in (&mut chunks).enumerate() {
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let px = pixels + i as u32;
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let px_x = px % self.bounds.width;
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let px_y = px / self.bounds.width;
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let scale_x = px_x as f32 * basis_scale_x;
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let scale_y = px_y as f32 * basis_scale_y;
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for (ComponentState { x, y, .. }, rgb) in self.factors.iter_mut() {
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let basis = f32::cos(*x as f32 * scale_x) * f32::cos(*y as f32 * scale_y);
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assert_eq!(chunk.len(), rgb.len());
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for (val, slot) in chunk
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.iter()
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.map(|byte| basis * srgb_to_linear(*byte))
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.zip(rgb)
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{
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*slot += val;
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}
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}
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}
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if !chunks.remainder().is_empty() {
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let px = pixels + (rgba8_image[offset..].len() / BYTES_PER_PIXEL) as u32;
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let px_x = px % self.bounds.width;
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let px_y = px / self.bounds.width;
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let scale_x = px_x as f32 * basis_scale_x;
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let scale_y = px_y as f32 * basis_scale_y;
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for (ComponentState { x, y, basis }, rgb) in self.factors.iter_mut() {
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*basis = f32::cos(*x as f32 * scale_x) * f32::cos(*y as f32 * scale_y);
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for (val, slot) in chunks
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.remainder()
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.iter()
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.map(|byte| *basis * srgb_to_linear(*byte))
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.zip(rgb)
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{
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*slot += val;
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}
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}
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}
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self.index += rgba8_image.len();
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}
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/// Produce a blurhash from the provided encoder
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pub fn finalize(mut self) -> String {
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for (ComponentState { x, y, .. }, rgb) in self.factors.iter_mut() {
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let normalisation = if *x == 0 && *y == 0 { 1. } else { 2. };
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let scale = normalisation / (self.bounds.width * self.bounds.height) as f32;
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for slot in rgb {
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*slot *= scale;
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}
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}
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let mut blurhash = String::with_capacity(30);
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let (_, dc) = self.factors[0];
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let ac = &self.factors[1..];
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let size_flag = self.components.x - 1 + (self.components.y - 1) * 9;
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base83::encode(size_flag, 1, &mut blurhash);
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let maximum = ac.iter().fold(0.0_f32, |maximum, (_, [r, g, b, _])| {
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maximum.max(r.abs()).max(g.abs()).max(b.abs())
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});
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let quantized_maximum = (maximum * 166. - 0.5).floor().max(0.) as u32;
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base83::encode(quantized_maximum, 1, &mut blurhash);
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let maximum_value = (quantized_maximum + 1) as f32 / 166.;
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base83::encode(encode_dc(dc), 4, &mut blurhash);
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for (_, rgb) in ac {
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base83::encode(encode_ac(*rgb, maximum_value), 2, &mut blurhash);
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}
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blurhash
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}
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}
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fn encode_dc(rgb: [f32; BYTES_PER_PIXEL]) -> u32 {
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let [r, g, b, _] = rgb.map(linear_to_srgb);
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(r << 16) + (g << 8) + b
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}
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fn encode_ac(rgb: [f32; BYTES_PER_PIXEL], maximum_value: f32) -> u32 {
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let [r, g, b, _] = rgb.map(|c| encode_ac_digit(c, maximum_value));
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r * 19 * 19 + g * 19 + b
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}
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fn encode_ac_digit(d: f32, maximum_value: f32) -> u32 {
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((sign_pow(d / maximum_value, 0.5) * 9. + 9.5) as i32).clamp(0, 18) as u32
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}
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fn linear_to_srgb(value: f32) -> u32 {
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let v = f32::max(0., f32::min(1., value));
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if v <= 0.003_130_8 {
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(v * 12.92 * 255. + 0.5).round() as u32
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} else {
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((1.055 * f32::powf(v, 1. / 2.4) - 0.055) * 255. + 0.5).round() as u32
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}
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}
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fn sign(n: f32) -> f32 {
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if n < 0. {
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-1.
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} else {
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1.
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}
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}
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fn sign_pow(val: f32, exp: f32) -> f32 {
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sign(val) * val.abs().powf(exp)
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}
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impl std::fmt::Display for ComponentError {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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write!(f, "Components out of bounds")
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}
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}
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impl std::error::Error for ComponentError {}
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#[cfg(test)]
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mod tests {
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use image::{EncodableLayout, GenericImageView};
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#[test]
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fn contrived() {
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let input = [
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0, 60, 120, 0, 0, 60, 120, 0, 0, 60, 120, 0, 0, 60, 120, 0, 0, 60, 120, 0, 0, 60, 120,
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0, 0, 60, 120, 0, 0, 60, 120, 0, 120, 60, 0, 0, 120, 60, 0, 0, 120, 60, 0, 0, 120, 60,
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0, 0, 120, 60, 0, 0, 120, 60, 0, 0, 120, 60, 0, 0, 120, 60, 0, 0,
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];
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let width = 4;
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let height = 4;
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let hash = super::encode(
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crate::Components { x: 4, y: 3 },
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crate::ImageBounds { width, height },
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&input,
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)
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.unwrap();
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assert_eq!(hash, "LQ9~?d$,fQ$,G1S%fQS%A{SPfQSP");
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}
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#[test]
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fn one_component() {
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let inputs = [
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("data/19dd1c444d1c7939.png", "00AQtR"),
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("data/f73d2ee39133d871.jpg", "00E{R{"),
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("data/shenzi.png", "0039[D"),
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];
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for (input, output) in inputs {
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let img = image::open(input).unwrap();
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let (width, height) = img.dimensions();
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let hash = super::encode(
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crate::Components { x: 1, y: 1 },
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crate::ImageBounds { width, height },
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img.to_rgba8().as_bytes(),
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)
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.unwrap();
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assert_eq!(hash, output, "expected output wrong");
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}
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}
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#[test]
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fn matches_blurhash() {
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let inputs = [
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("data/19dd1c444d1c7939.png", "L3AQtR2FSz6NrsOCW:ODR*,EE};h"),
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("data/f73d2ee39133d871.jpg", "LJE{R{Z}V?N#0JR*Rit7^htTfkaI"),
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("data/shenzi.png", "L239[DQ.91t,rJX9Qns+8zt5.PR6"),
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];
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for (input, output) in inputs {
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let img = image::open(input).unwrap();
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let (width, height) = img.dimensions();
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let hash = super::encode(
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crate::Components { x: 4, y: 3 },
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crate::ImageBounds { width, height },
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img.to_rgba8().as_bytes(),
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)
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.unwrap();
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assert_eq!(hash, output, "expected output wrong");
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}
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}
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#[test]
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fn matches_self_when_split() {
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let inputs = [
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"data/19dd1c444d1c7939.png",
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"data/f73d2ee39133d871.jpg",
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"data/shenzi.png",
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];
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for input in inputs {
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let img = image::open(input).unwrap();
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let (width, height) = img.dimensions();
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let rgba8_img = img.to_rgba8();
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let bytes = rgba8_img.as_bytes();
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let b1 = super::encode(
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crate::Components { x: 4, y: 3 },
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crate::ImageBounds { width, height },
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bytes,
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)
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.unwrap();
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for chunk_count in 2..20 {
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let mut encoder = super::Encoder::new(
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crate::Components { x: 4, y: 3 },
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crate::ImageBounds { width, height },
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)
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.unwrap();
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let chunk_size = bytes.len() / chunk_count;
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for chunk in bytes.chunks(chunk_size) {
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encoder.update(chunk);
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}
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let b2 = encoder.finalize();
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assert_eq!(b1, b2);
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}
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}
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}
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}
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