| use crate::{CHANNELS_IN_RGB, Histogram, Image, Pixel}; |
| use std::f64::consts::E; |
|
|
| impl Image<u16> { |
| pub fn gamma_correction_fn(&self, histogram: &Histogram) -> impl Fn(Pixel) -> [u16; CHANNELS_IN_RGB] + use<> { |
| let percentage = self.width * self.height; |
|
|
| let mut white = 0; |
| for channel_histogram in histogram { |
| let mut total = 0; |
| for i in (0x20..0x2000).rev() { |
| total += channel_histogram[i] as u64; |
|
|
| if total * 100 > percentage as u64 { |
| white = white.max(i); |
| break; |
| } |
| } |
| } |
|
|
| let curve = generate_gamma_curve(0.45, 4.5, (white << 3) as f64); |
|
|
| move |pixel: Pixel| pixel.values.map(|value| curve[value as usize]) |
| } |
| } |
|
|
| |
| fn generate_gamma_curve(power: f64, threshold: f64, max_intensity: f64) -> Vec<u16> { |
| debug_assert!(max_intensity != 0.); |
|
|
| let (mut bound_start, mut bound_end) = if threshold >= 1. { (0., 1.) } else { (1., 0.) }; |
|
|
| let mut transition_point = 0.; |
| let mut transition_ratio = 0.; |
| let mut curve_adjustment = 0.; |
|
|
| if threshold != 0. && (threshold - 1.) * (power - 1.) <= 0. { |
| for _ in 0..48 { |
| transition_point = (bound_start + bound_end) / 2.; |
|
|
| if power != 0. { |
| let temp_transition_ratio = transition_point / threshold; |
| let exponential_power = temp_transition_ratio.powf(-power); |
| let normalized_exponential_power = (exponential_power - 1.) / power; |
| let comparison_result = normalized_exponential_power - (1. / transition_point); |
|
|
| let bound_to_update = if comparison_result > -1. { &mut bound_end } else { &mut bound_start }; |
| *bound_to_update = transition_point; |
| } else { |
| let adjusted_transition_point = E.powf(1. - 1. / transition_point); |
| let transition_point_ratio = transition_point / adjusted_transition_point; |
|
|
| let bound_to_update = if transition_point_ratio < threshold { &mut bound_end } else { &mut bound_start }; |
| *bound_to_update = transition_point; |
| } |
| } |
|
|
| transition_ratio = transition_point / threshold; |
|
|
| if power != 0. { |
| curve_adjustment = transition_point * ((1. / power) - 1.); |
| } |
| } |
|
|
| let mut curve = vec![0xffff; 0x1_0000]; |
| let length = curve.len() as f64; |
|
|
| for (i, entry) in curve.iter_mut().enumerate() { |
| let ratio = (i as f64) / max_intensity; |
| if ratio < 1. { |
| let altered_ratio = if ratio < transition_ratio { |
| ratio * threshold |
| } else if power != 0. { |
| ratio.powf(power) * (1. + curve_adjustment) - curve_adjustment |
| } else { |
| ratio.ln() * transition_point + 1. |
| }; |
|
|
| *entry = (length * altered_ratio) as u16; |
| } |
| } |
|
|
| curve |
| } |
|
|
