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//! A line thinning library for binary images, including edge detection and //! threshold functions for preprocessing images into binary images. //! //! The goal of thinning is to remove excess pixels from the image until the //! lines present are one pixel wide, resembling a "skeleton" of the original //! pattern. //! //! The thinning algorithms are based on the papers *Zhang & Suen, 1984* and //! *Chen & Hsu, 1988*. See [Reference](#reference). //! //! ## Usage //! //! There are three main workflows for thinning images with this library. The //! second and third workflows produce binarized images with library functions //! before thinning the image. //! //! The generic [`ForegroundColor`](crate::ForegroundColor) parameter on //! [`edge_detection::sobel`][sobel], [`edge_detection::sobel4`][sobel4], and //! [`thin_image_edges`](crate::thin_image_edges) specifies what foreground and //! background colors the resulting //! [`thin_image_edges`](crate::thin_image_edges) image will produce. The //! foreground color is the color of the line to be thinned. A foreground color //! of white will have a black background and a foreground of black will have a //! white background. The generic parameters must match when using an edge //! detection function in combination with the thinning function. //! //! [sobel]: crate::edge_detection::sobel //! [sobel4]: crate::edge_detection::sobel4 //! //! An example program can be viewed at `/examples/skeletonize.rs`. //! //! #### No preprocessing //! //! The image is already binarized so the edges can be thinned immediately. //! //! ``` //! # fn main() -> Result<(), skeletonize::error::SkeletonizeError> { //! use skeletonize::{foreground, thin_image_edges, MarkingMethod}; //! //! # let image_buffer = image::ImageBuffer::from_pixel(1, 1, image::Rgb([255, 255, 255])); //! # let mut img = image::DynamicImage::ImageRgb8(image_buffer).grayscale(); //! let method = MarkingMethod::Modified; //! //! thin_image_edges::<foreground::Black>(&mut img, method, None)?; //! # Ok(()) //! # } //! ``` //! //! If this produces poor results and/or takes a long time to run: //! - the incorrect foreground color may have been chosen - try using the //! opposite color, or //! - the image may not be binary and needs to be thresholded. //! //! #### Edge detection //! //! Run an edge detection filter on the image and threshold those results before //! thinning the lines. Note that the foreground color parameters must match on //! the edge detection function and the thinning function. //! //! ``` //! # fn main() -> Result<(), skeletonize::error::SkeletonizeError> { //! use skeletonize::edge_detection::sobel4; //! use skeletonize::{foreground, thin_image_edges, MarkingMethod}; //! //! # let image_buffer = image::ImageBuffer::from_pixel(2, 2, image::Rgb([255, 255, 255])); //! # let img = image::DynamicImage::ImageRgb8(image_buffer).grayscale(); //! let method = MarkingMethod::Modified; //! let threshold = Some(0.1); //! //! let mut filtered = sobel4::<foreground::White>(&img, threshold)?; //! thin_image_edges::<foreground::White>(&mut filtered, method, None)?; //! # Ok(()) //! # } //! ``` //! //! #### Thresholding //! //! Threshold the image before thinning, e.g., cleaning up a grayscale image. //! //! ``` //! # fn main() -> Result<(), skeletonize::error::SkeletonizeError> { //! use skeletonize::{foreground, thin_image_edges, threshold, MarkingMethod}; //! //! # let image_buffer = image::ImageBuffer::from_pixel(2, 2, image::Rgb([255, 255, 255])); //! # let mut img = image::DynamicImage::ImageRgb8(image_buffer).grayscale(); //! let method = MarkingMethod::Modified; //! let threshold = 0.1; //! //! skeletonize::threshold(&mut img, threshold)?; //! thin_image_edges::<foreground::Black>(&mut img, method, None)?; //! # Ok(()) //! # } //! ``` //! //! ## Reference //! //! Zhang, T. Y. & Suen, C. Y. (1984). A fast parallel algorithm for thinning //! digital patterns. Commun. ACM 27, 3 (March 1984), 236–239. //! [DOI:10.1145/357994.358023](https://doi.org/10.1145/357994.358023) //! //! Chen, Yung-Sheng & Hsu, Wen-Hsing. (1988). A modified fast parallel //! algorithm for thinning digital patterns. Pattern Recognition Letters. 7. //! 99-106. //! [DOI:10.1016/0167-8655(88)90124-9](https://doi.org/10.1016/0167-8655(88)90124-9) #![warn(missing_docs, rust_2018_idioms, unsafe_code)] pub mod edge_detection; pub mod error; pub mod neighbors; mod thinning; use error::{LumaConversionErrorKind, SkeletonizeError}; pub use thinning::thin_image_edges; /// Represents the color of the foreground or features in a binary image. For /// example, white text on a black background has a white foreground color and /// black background color. pub trait ForegroundColor { /// The background color of the image for binarization. const BACKGROUND_COLOR: u8; } /// Implementations of [`ForegroundColor`](crate::ForegroundColor). pub mod foreground { /// Black foreground color, represented as `0`. pub struct Black; impl crate::ForegroundColor for Black { const BACKGROUND_COLOR: u8 = 255; } /// White foreground color, represented by `255`. pub struct White; impl crate::ForegroundColor for White { const BACKGROUND_COLOR: u8 = 0; } } /// 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, } impl Edge { /// Convert the edge status into a `u8` representation. pub fn to_u8(&self) -> u8 { match self { Self::Empty | Self::DoesNotExist => 0, Self::Filled => 1, } } } /// The algorithm that determines which pixels are removed during the edge /// thinning process. /// /// ### Reference /// /// <span id="standard"></span>Zhang, T. Y. & Suen, C. Y. (1984). A fast /// parallel algorithm for thinning digital patterns. Commun. ACM 27, 3 (March /// 1984), 236–239. /// [DOI:10.1145/357994.358023](https://doi.org/10.1145/357994.358023) /// /// <span id="modified"></span>Chen, Yung-Sheng & Hsu, Wen-Hsing. (1988). A /// modified fast parallel algorithm for thinning digital patterns. Pattern /// Recognition Letters. 7. 99-106. /// [DOI:10.1016/0167-8655(88)90124-9](https://doi.org/10.1016/0167-8655(88)90124-9) #[derive(Clone, Copy, Debug, PartialEq)] pub enum MarkingMethod { /// An algorithm based on `Zhang and Suen, 1984`. /// /// See [MarkingMethod](crate::MarkingMethod#standard) for reference. Standard, /// An improved and slightly more complex algorithm than `Standard` based on /// `Chen and Hsu, 1988`. This algorithm improves on the original's /// weaknesses with generally thinner lines and better line connectivity. /// /// See [MarkingMethod](crate::MarkingMethod#modified) for reference. Modified, } impl Default for MarkingMethod { fn default() -> Self { Self::Modified } } /// Create a binary image where values below `threshold` become black and above /// become white. `threshold` ranges from 0.0 to 1.0. pub fn threshold(img: &mut image::DynamicImage, threshold: f32) -> Result<(), SkeletonizeError> { for pix in img .as_mut_luma8() .ok_or(SkeletonizeError::LumaConversion( LumaConversionErrorKind::ThresholdMutableLuma, ))? .iter_mut() { *pix = if *pix < (threshold * 255.0).round() as u8 { 0 } else { 255 }; } Ok(()) }