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Bitmap/Histogram: Difference between revisions
add Rust section
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(add Rust section) |
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Pixmap.open('file.ppm').save_as_blackandwhite('file_bw.ppm')</lang>
=={{header|Rust}}==
<lang rust>extern crate image;
use image::{DynamicImage, GenericImageView, ImageBuffer, Rgba};
/// index of the alpha channel in RGBA
const ALPHA: usize = 3;
/// Computes the luminance of a single pixel
/// Result lies within `u16::MIN..u16::MAX`
const fn luminance(rgba: Rgba<u8>) -> u16 {
let Rgba([r, g, b, _a]) = rgba;
55 * r as u16 + 183 * g as u16 + 19 * b as u16
}
/// computes the median of a given histogram
/// Result lies within `u16::MIN..u16::MAX`
fn get_median(total: usize, histogram: &[usize]) -> u16 {
let mut sum = 0;
for (index, &count) in histogram.iter().enumerate() {
sum += count;
if sum >= total / 2 {
return index as u16;
}
}
u16::MAX
}
/// computes the histogram of a given image
fn compute_histogram(img: &DynamicImage) -> Vec<usize> {
let mut histogram = vec![0; 1 << u16::BITS];
img.pixels()
.map(|(_x, _y, pixel)| luminance(pixel))
.for_each(|luminance| histogram[luminance as usize] += 1);
histogram
}
/// returns a black or white pixel with an alpha value
const fn black_white(is_white: bool, alpha: u8) -> [u8; 4] {
if is_white {
[255, 255, 255, alpha]
} else {
[0, 0, 0, alpha]
}
}
/// create a monochome compy of the given image
/// preserves alpha data
fn convert_to_monochrome(img: &DynamicImage) -> ImageBuffer<Rgba<u8>, Vec<u8>> {
let histogram = compute_histogram(img);
let (width, height) = img.dimensions();
let pixel_count = (width * height) as usize;
let median = get_median(pixel_count, &histogram);
let pixel_buffer = img.pixels()
.flat_map(|(_x, _y, pixel)| black_white(luminance(pixel) > median, pixel[ALPHA]))
.collect();
ImageBuffer::from_vec(width, height, pixel_buffer).unwrap_or_else(|| unreachable!())
}
fn main() {
let img = image::open("lena.jpg").expect("could not load image file");
let img = convert_to_monochrome(&img);
img.save("lena-mono.png").expect("could not save result image");
}
</lang>
=={{header|Scala}}==
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