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Expand stetch_contrast() to color images also using u8 #670

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Aug 18, 2024
Merged

Expand stetch_contrast() to color images also using u8 #670

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51 changes: 28 additions & 23 deletions src/contrast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,13 +2,13 @@

use std::cmp::{max, min};

use image::{GrayImage, Luma};
use image::{GrayImage, Luma, Pixel};
#[cfg(feature = "rayon")]
use rayon::prelude::*;

use crate::definitions::{HasBlack, HasWhite};
use crate::definitions::{HasBlack, HasWhite, Image};
use crate::integral_image::{integral_image, sum_image_pixels};
use crate::map::map_subpixels_mut;
use crate::map::map_pixels_mut;
use crate::stats::{cumulative_histogram, histogram};

/// Applies an adaptive threshold to an image.
Expand Down Expand Up @@ -276,13 +276,16 @@ pub fn equalize_histogram_mut(image: &mut GrayImage) {
///
/// # Panics
/// If `input_lower >= input_upper` or `output_lower > output_upper`.
pub fn stretch_contrast(
image: &GrayImage,
pub fn stretch_contrast<P>(
image: &Image<P>,
input_lower: u8,
input_upper: u8,
output_lower: u8,
output_upper: u8,
) -> GrayImage {
) -> Image<P>
where
P: Pixel<Subpixel = u8>,
{
let mut out = image.clone();
stretch_contrast_mut(
&mut out,
Expand All @@ -294,13 +297,15 @@ pub fn stretch_contrast(
out
}
#[doc=generate_mut_doc_comment!("stretch_contrast")]
pub fn stretch_contrast_mut(
image: &mut GrayImage,
pub fn stretch_contrast_mut<P>(
image: &mut Image<P>,
input_min: u8,
input_max: u8,
output_min: u8,
output_max: u8,
) {
) where
P: Pixel<Subpixel = u8>,
{
assert!(
input_min < input_max,
"input_min must be smaller than input_max"
Expand All @@ -318,21 +323,21 @@ pub fn stretch_contrast_mut(
let input_width = input_max - input_min;
let output_width = output_max - output_min;

let f = |p: u8| {
let p: u16 = p.into();
let f = |p: P| {
p.map_without_alpha(|c| {
let c = u16::from(c);

let output = if p <= input_min {
output_min
} else if p >= input_max {
output_max
} else {
(((p - input_min) * output_width) / input_width) + output_min
};

output as u8
if c <= input_min {
(output_min) as u8
} else if c >= input_max {
(output_max) as u8
} else {
((((c - input_min) * output_width) / input_width) + output_min) as u8
}
})
};

map_subpixels_mut(image, f);
map_pixels_mut(image, f);
}

/// Adjusts contrast of an 8bpp grayscale image so that its
Expand Down Expand Up @@ -454,12 +459,12 @@ mod tests {
let mut image = GrayImage::from_pixel(3, 3, Luma([100u8]));
image.put_pixel(2, 2, Luma::black());

//big delta should make the theshold for the black pixel small enough to be white
//big delta should make the threshold for the black pixel small enough to be white
let binary = adaptive_threshold(&image, 1, 100);
let expected = GrayImage::from_pixel(3, 3, Luma::white());
assert_pixels_eq!(binary, expected);

//smaller delta should make the theshold the pixel to be black
//smaller delta should make the threshold the pixel to be black
let binary = adaptive_threshold(&image, 1, 50);
let mut expected = GrayImage::from_pixel(3, 3, Luma::white());
expected.put_pixel(2, 2, Luma::black());
Expand Down
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