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Henning stroeker #19

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d425cf1
Initial commit
Oct 8, 2025
6995029
lut optimizations
Oct 8, 2025
c20942e
enumerate_pixels_mut after clone
Oct 8, 2025
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100 changes: 62 additions & 38 deletions src/lut_filters.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,8 @@
/// - Learn when LUTs are appropriate
use image::{ImageBuffer, Rgb, RgbImage};

use crate::lut_filters::naive::apply_brightness_contrast_gamma_impl;

pub fn apply_brightness_contrast(img: &RgbImage, brightness: i16, contrast: f32) -> RgbImage {
naive::apply_brightness_contrast(img, brightness, contrast)
}
Expand All @@ -31,58 +33,80 @@ pub fn apply_brightness_contrast_gamma(
contrast: f32,
gamma: f32,
) -> RgbImage {
let temp_img = apply_brightness_contrast(img, brightness, contrast);
naive::apply_gamma(&temp_img, gamma)
apply_brightness_contrast_gamma_impl(img, brightness, contrast, gamma)
}

mod naive {

use super::*;

/// Apply brightness and contrast with floating-point math per pixel
pub fn apply_brightness_contrast(img: &RgbImage, brightness: i16, contrast: f32) -> RgbImage {
let (width, height) = img.dimensions();
let mut output = ImageBuffer::new(width, height);

for (x, y, pixel) in img.enumerate_pixels() {
let r = pixel[0] as f32;
let g = pixel[1] as f32;
let b = pixel[2] as f32;

// Apply contrast and brightness (5 FP ops per channel!)
let r = ((r - 128.0) * (1.0 + contrast)) + 128.0 + brightness as f32;
let g = ((g - 128.0) * (1.0 + contrast)) + 128.0 + brightness as f32;
let b = ((b - 128.0) * (1.0 + contrast)) + 128.0 + brightness as f32;

output.put_pixel(
x,
y,
Rgb([
r.clamp(0.0, 255.0) as u8,
g.clamp(0.0, 255.0) as u8,
b.clamp(0.0, 255.0) as u8,
]),
);
pub fn apply_brightness_contrast_gamma_impl(
img: &RgbImage,
brightness: i16,
contrast: f32,
gamma: f32,
) -> RgbImage {
let mut lut = [0u8; 256];
for i in 0..256 {
let mut a = ((i as f32 - 128.0) * (1.0 + contrast)) + 128.0 + brightness as f32;
a = (a / 255.0).powf(1.0 / gamma) * 255.0;
lut[i] = a.clamp(0.0, 255.0).round() as u8;
}
apply_lut(img, &lut)
}

// pub fn apply_lut(img: &RgbImage, lut: &[u8; 256]) -> RgbImage {
// let (width, height) = img.dimensions();
// let mut output = ImageBuffer::new(width, height);

// for (x, y, pixel) in img.enumerate_pixels() {
// output.put_pixel(
// x,
// y,
// Rgb([
// lut[pixel[0] as usize],
// lut[pixel[1] as usize],
// lut[pixel[2] as usize],
// ]),
// );
// }

// output
// }

pub fn apply_lut(img: &RgbImage, lut: &[u8; 256]) -> RgbImage {
let mut output = img.clone();

output.enumerate_pixels_mut().for_each(|(_, _, pixel)| {
*pixel = Rgb([
lut[pixel[0] as usize],
lut[pixel[1] as usize],
lut[pixel[2] as usize],
]);
});

output
}

/// Apply brightness and contrast with floating-point math per pixel
pub fn apply_brightness_contrast(img: &RgbImage, brightness: i16, contrast: f32) -> RgbImage {
let mut lut = [0u8; 256];
for i in 0..256 {
lut[i] = (((i as f32 - 128.0) * (1.0 + contrast)) + 128.0 + brightness as f32)
.clamp(0.0, 255.0)
.round() as u8;
}
apply_lut(img, &lut)
}

/// Naive implementation: Apply gamma correction
/// This is VERY slow because powf() is expensive!
pub fn apply_gamma(img: &RgbImage, gamma: f32) -> RgbImage {
let (width, height) = img.dimensions();
let mut output = ImageBuffer::new(width, height);

for (x, y, pixel) in img.enumerate_pixels() {
// powf() is VERY expensive - this is why we need a LUT!
let r = (pixel[0] as f32 / 255.0).powf(1.0 / gamma) * 255.0;
let g = (pixel[1] as f32 / 255.0).powf(1.0 / gamma) * 255.0;
let b = (pixel[2] as f32 / 255.0).powf(1.0 / gamma) * 255.0;

output.put_pixel(x, y, Rgb([r as u8, g as u8, b as u8]));
let mut lut = [0u8; 256];
for i in 0..256 {
lut[i] = ((i as f32 / 255.0).powf(1.0 / gamma) * 255.0).round() as u8;
}

output
apply_lut(img, &lut)
}
}

Expand Down