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216const BACKGROUND_COLOR: u8 = 255;
/// Classification of pixels in an image used for edge thinning.
#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum Edge {
/// The pixel does not contain the foreground color.
Empty = 0,
/// The pixel contains the foreground color.
Filled = 1,
/// The pixel is not a valid location within the image.
DoesNotExist,
}
use image::Luma;
/// Struct with information describing the surrounding pixels.
pub struct NeighborInfo {
/// The number of neighbor pixels with non-background color.
pub filled: u8,
/// The number of surrounding pixels.
pub neighbors: u8,
/// An array containing the [status](crate::Edge) of the neighboring pixels.
pub edge_status: [Edge; 8],
}
/// Calculate and return a [`NeighborInfo`](crate::neighbors::NeighborInfo)
/// struct which contains the number of occupied neighbor pixels, number of
/// neighbor pixels, and the [edge status](crate::Edge) of the neighboring
/// pixels.
pub fn get_neighbor_info(
img: &image::GrayImage,
width: u32,
height: u32,
x: u32,
y: u32,
) -> NeighborInfo {
let mut filled = 0;
let mut neighbors = 0;
let p9 = if y > 0 && x > 0 {
neighbors += 1;
if img.get_pixel(x - 1, y - 1)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
let p2 = if y > 0 {
neighbors += 1;
if img.get_pixel(x, y - 1)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
let p3 = if y > 0 && x < u32::MAX && x + 1 < width {
neighbors += 1;
if img.get_pixel(x + 1, y - 1)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
let p8 = if x > 0 {
neighbors += 1;
if img.get_pixel(x - 1, y)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
let p4 = if x < u32::MAX && x + 1 < width {
neighbors += 1;
if img.get_pixel(x + 1, y)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
let p7 = if x > 0 && y < u32::MAX && y + 1 < height {
neighbors += 1;
if img.get_pixel(x - 1, y + 1)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
let p6 = if y < u32::MAX && y + 1 < height {
neighbors += 1;
if img.get_pixel(x, y + 1)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
let p5 = if x < u32::MAX && x + 1 < width && y < u32::MAX && y + 1 < height {
neighbors += 1;
if img.get_pixel(x + 1, y + 1)[0] != BACKGROUND_COLOR {
filled += 1;
Edge::Filled
} else {
Edge::Empty
}
} else {
Edge::DoesNotExist
};
NeighborInfo {
filled,
neighbors,
edge_status: [p2, p3, p4, p5, p6, p7, p8, p9],
}
}
pub fn thin_image_edges(img_in: &image::GrayImage) -> image::GrayImage {
let mut img = img_in.clone();
let mut pixels_to_remove = Vec::new();
let mut phase_one = true;
loop {
// Mark pixels to remove
for (x, y, p) in img.enumerate_pixels() {
if p.0[0] == BACKGROUND_COLOR {
continue;
}
let info = get_neighbor_info(&img, img.width(), img.height(), x, y);
let [p2, p3, p4, p5, p6, p7, p8, p9] = info.edge_status;
if !(2..=7).contains(&info.filled) || info.neighbors != 8 {
continue;
}
let mut transitions = 0;
for pair in [p2, p3, p4, p5, p6, p7, p8, p9, p2].windows(2) {
if pair[0] == Edge::Empty && pair[1] == Edge::Filled {
transitions += 1;
}
}
if !(transitions == 1 || transitions == 2) {
continue;
}
if phase_one {
if transitions == 1 {
if (p2 == Edge::Empty || p4 == Edge::Empty || p6 == Edge::Empty)
&& (p4 == Edge::Empty || p6 == Edge::Empty || p8 == Edge::Empty)
{
pixels_to_remove.push((x, y));
}
} else {
if ((p2 == Edge::Filled && p4 == Edge::Filled)
&& (p6 == Edge::Empty && p7 == Edge::Empty && p8 == Edge::Empty))
|| ((p4 == Edge::Filled && p6 == Edge::Filled)
&& (p2 == Edge::Empty && p8 == Edge::Empty && p9 == Edge::Empty))
{
pixels_to_remove.push((x, y));
}
}
} else {
if transitions == 1 {
if (p2 == Edge::Empty || p4 == Edge::Empty || p8 == Edge::Empty)
&& (p2 == Edge::Empty || p6 == Edge::Empty || p8 == Edge::Empty)
{
pixels_to_remove.push((x, y));
}
} else {
if ((p2 == Edge::Filled && p8 == Edge::Filled)
&& (p4 == Edge::Empty && p5 == Edge::Empty && p6 == Edge::Empty))
|| ((p6 == Edge::Filled && p8 == Edge::Filled)
&& (p2 == Edge::Empty && p3 == Edge::Empty && p4 == Edge::Empty))
{
pixels_to_remove.push((x, y));
}
}
}
}
phase_one = !phase_one;
// Replace marked pixels with background color to thin the edges
for &(x, y) in &pixels_to_remove {
img.put_pixel(x, y, Luma([BACKGROUND_COLOR]));
}
if pixels_to_remove.is_empty() {
return img;
}
pixels_to_remove.clear();
}
}