Merge pull request #7 from whisperfish/lookup-table

Add lookup table for srgb_to_linear

Cargo.toml

@@ -19,3 +19,7 @@ criterion = "0.5"
 [[bench]]
 name = "decode"
 harness = false
+
+[[bench]]
+name = "encode"
+harness = false

benches/encode.rs

@@ -0,0 +1,18 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use image::GenericImageView;
+
+pub fn lenna(c: &mut Criterion) {
+    for case in ["data/SIPI_Jelly_Beans.tiff", "data/octocat.png"] {
+        let img = image::open(case).unwrap();
+
+        let (width, height) = img.dimensions();
+        let img = img.to_rgba8();
+
+        c.bench_function(&format!("encode {}", case), |b| {
+            b.iter(|| blurhash::encode(4, 3, width, height, black_box(&img)).unwrap());
+        });
+    }
+}
+
+criterion_group!(benches, lenna);
+criterion_main!(benches);

build.rs

@@ -0,0 +1,28 @@
+use std::io::Write;
+
+/// srgb 0-255 integer to linear 0.0-1.0 floating point conversion.
+pub fn srgb_to_linear(value: u32) -> f32 {
+    let v = value as f32 / 255.;
+    if v <= 0.04045 {
+        v / 12.92
+    } else {
+        f32::powf((v + 0.055) / 1.055, 2.4)
+    }
+}
+
+fn generate_srgb_lookup() -> [f32; 256] {
+    let mut table = [0f32; 256];
+    for (i, val) in table.iter_mut().enumerate() {
+        *val = srgb_to_linear(i as u32);
+    }
+    table
+}
+
+fn main() {
+    let table = generate_srgb_lookup();
+
+    let out_dir = std::env::var("OUT_DIR").unwrap();
+    let out_dir = std::path::PathBuf::from(out_dir);
+    let mut f = std::fs::File::create(out_dir.join("srgb_lookup.rs")).unwrap();
+    writeln!(f, "static SRGB_LOOKUP: [f32; 256] = {:?};", table).unwrap();
+}

src/lib.rs

@@ -6,7 +6,7 @@
 //! use blurhash::encode;
 //! use image::{GenericImageView, EncodableLayout};
 //!
-//! let img = image::open("octocat.png").unwrap();
+//! let img = image::open("data/octocat.png").unwrap();
 //! let (width, height) = img.dimensions();
 //! let blurhash = encode(4, 3, width, height, img.to_rgba().as_bytes()).unwrap();
 //!
@@ -231,12 +231,12 @@ mod tests {
 
     #[test]
     fn decode_blurhash() {
-        let img = image::open("octocat.png").unwrap();
+        let img = image::open("data/octocat.png").unwrap();
         let (width, height) = img.dimensions();
 
         let blurhash = encode(4, 3, width, height, img.to_rgba8().as_bytes()).unwrap();
         let img = decode(&blurhash, width, height, 1.0).unwrap();
-        save_buffer("out.png", &img, width, height, Rgba8).unwrap();
+        save_buffer("data/out.png", &img, width, height, Rgba8).unwrap();
 
         assert_eq!(img[0..5], [45, 1, 56, 255, 45]);
     }

src/util.rs

@@ -1,3 +1,5 @@
+include!(concat!(env!("OUT_DIR"), "/srgb_lookup.rs"));
+
 /// linear 0.0-1.0 floating point to srgb 0-255 integer conversion.
 pub fn linear_to_srgb(value: f32) -> u32 {
     let v = f32::max(0., f32::min(1., value));
@@ -10,12 +12,7 @@ pub fn linear_to_srgb(value: f32) -> u32 {
 
 /// srgb 0-255 integer to linear 0.0-1.0 floating point conversion.
 pub fn srgb_to_linear(value: u32) -> f32 {
-    let v = value as f32 / 255.;
-    if v <= 0.04045 {
-        v / 12.92
-    } else {
-        f32::powf((v + 0.055) / 1.055, 2.4)
-    }
+    SRGB_LOOKUP[value as usize]
 }
 
 fn sign(n: f32) -> f32 {