Added working otsu and mean thresholding

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Added
 * Padding strategies (`NoPadding`, `ConstantPadding`, `ZeroPadding`)
+* Threshold module with Otsu and Mean threshold algorithms
 
 ### Changed
 * Integrated Padding strategies into convolutions

Cargo.toml

@@ -19,3 +19,5 @@ num-traits = "0.2"
 [dev-dependencies]
 ndarray-rand = "0.9.0"
 rand = "0.6.5"
+assert_approx_eq = "1.1.0"
+noisy_float = "0.1.11"

src/processing/mod.rs

@@ -8,12 +8,15 @@ pub mod filter;
 pub mod kernels;
 /// Sobel operator for edge detection
 pub mod sobel;
+/// Thresholding functions
+pub mod threshold;
 
 pub use canny::*;
 pub use conv::*;
 pub use filter::*;
 pub use kernels::*;
 pub use sobel::*;
+pub use threshold::*;
 
 /// Common error type for image processing algorithms
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]

src/processing/threshold.rs

@@ -0,0 +1,273 @@
+use crate::core::{ColourModel, Image};
+use crate::core::{PixelBound};
+use crate::processing::*;
+use ndarray::prelude::*;
+use num_traits::cast::{FromPrimitive};
+use num_traits::cast::{ToPrimitive};
+use ndarray_stats::QuantileExt;
+use ndarray_stats::HistogramExt;
+use ndarray_stats::histogram::{Grid, Bins, Edges};
+use num_traits::{Num, NumAssignOps};
+use std::marker::PhantomData;
+
+// Development
+#[cfg(test)]
+use assert_approx_eq::assert_approx_eq;
+#[cfg(test)]
+use noisy_float::types::n64;
+
+
+/// Runs the Otsu Thresholding algorithm on a type T
+pub trait ThresholdOtsuExt<T> {
+    /// Output type, this is different as Otsu outputs a binary image
+    type Output;
+
+    /// Run the Otsu threshold detection algorithm with the 
+    /// given parameters. Due to Otsu being specified as working 
+    /// on greyscale images all current implementations
+    /// assume a single channel image returning an error otherwise.
+    fn threshold_otsu(&self) -> Result<Self::Output, Error>;
+}
+
+/// Runs the Mean Thresholding algorithm on a type T
+pub trait ThresholdMeanExt<T> {
+    /// Output type, this is different as Otsu outputs a binary image
+    type Output;
+
+    /// Run the Otsu threshold detection algorithm with the 
+    /// given parameters. Due to Otsu being specified as working 
+    /// on greyscale images all current implementations
+    /// assume a single channel image returning an error otherwise.
+    fn threshold_mean(&self) -> Result<Self::Output, Error>;
+}
+
+impl<T, C> ThresholdOtsuExt<T> for Image<T, C>
+where
+    Image<T, C>: Clone,
+    T: Copy + Clone + Ord + Num + NumAssignOps + ToPrimitive + FromPrimitive + PixelBound,
+    C: ColourModel,
+{
+    type Output = Image<bool, C>;
+
+    fn threshold_otsu(&self) -> Result<Self::Output, Error> {
+        let data = self.data.threshold_otsu()?;
+        Ok(Self::Output {
+            data,
+            model: PhantomData,
+        })
+    }
+}
+
+impl<T> ThresholdOtsuExt<T> for Array3<T>
+where
+    T: Copy + Clone + Ord + Num + NumAssignOps + ToPrimitive + FromPrimitive 
+{
+    type Output = Array3<bool>;
+
+    fn threshold_otsu(&self) -> Result<Self::Output, Error> {
+        if self.shape()[2] > 1 {
+            Err(Error::ChannelDimensionMismatch)
+        } else {
+            let value = calculate_threshold_otsu(&self)?;
+            let mask = apply_threshold(self, value);
+            Ok(mask)
+        }
+    }
+}
+
+///
+/// Calculates Otsu's threshold 
+/// Works per channel, but currently 
+/// assumes grayscale (see the error above if number of channels is > 1
+/// i.e. single channel; otherwise we need to output all 3 threshold values). 
+/// Todo: Add optional nbins
+///
+fn calculate_threshold_otsu<T>(mat: &Array3<T>) -> Result<f64, Error>
+where
+    T: Copy + Clone + Ord + Num + NumAssignOps + ToPrimitive + FromPrimitive 
+{
+    let mut threshold = 0.0;
+    let n_bins = 255;
+    for c in mat.axis_iter(Axis(2)) {
+        let scale_factor = (n_bins) as f64
+            /(c.max().unwrap().to_f64().unwrap()); 
+        let edges_vec: Vec<u8> = (0..n_bins).collect();
+        let grid = Grid::from(vec![Bins::new(Edges::from(edges_vec))]);
+
+        // get the histogram
+        let flat = Array::from_iter(c.iter()).insert_axis(Axis(1));
+        let flat2 = flat.mapv(
+            |x| ((*x).to_f64().unwrap() * scale_factor).to_u8().unwrap()
+        );
+        let hist = flat2.histogram(grid);
+        // Straight out of wikipedia: 
+        let counts = hist.counts(); 
+        let total = counts.sum().to_f64().unwrap();
+        let counts = Array::from_iter(counts.iter());
+        // NOTE: Could use the cdf generation for skimage-esque implementation 
+        // which entails a cumulative sum of the standard histogram 
+        let mut sum_b = 0.0;
+        let mut weight_b = 0.0;
+        let mut maximum = 0.0;
+        let mut level = 0.0;
+        let mut sum_intensity = 0.0;
+        for (index, count) in counts.indexed_iter(){
+            sum_intensity += (index as f64) * (*count).to_f64().unwrap();
+        }
+        for (index, count) in counts.indexed_iter(){
+            weight_b = weight_b + count.to_f64().unwrap();
+            sum_b = sum_b + (index as f64)* count.to_f64().unwrap();
+            let weight_f = total - weight_b;
+            if (weight_b > 0.0) && (weight_f > 0.0){
+                let mean_f = (sum_intensity - sum_b) / weight_f;
+                let val = weight_b * weight_f 
+			* ((sum_b / weight_b) - mean_f) 
+			* ((sum_b / weight_b) - mean_f);
+                if val > maximum{
+                    level = 1.0 + (index as f64);
+                    maximum = val;
+                }
+            }
+        }
+        threshold = level as f64 / scale_factor; 
+    }
+    Ok(threshold)
+}
+
+impl<T, C> ThresholdMeanExt<T> for Image<T, C>
+where
+    Image<T, C>: Clone,
+    T: Copy + Clone + Ord + Num + NumAssignOps + ToPrimitive + FromPrimitive + PixelBound,
+    C: ColourModel,
+{
+    type Output = Image<bool, C>;
+
+    fn threshold_mean(&self) -> Result<Self::Output, Error> {
+        let data = self.data.threshold_mean()?;
+        Ok(Self::Output {
+            data,
+            model: PhantomData,
+        })
+    }
+}
+
+impl<T> ThresholdMeanExt<T> for Array3<T>
+where
+    T: Copy + Clone + Ord + Num + NumAssignOps + ToPrimitive + FromPrimitive 
+{
+    type Output = Array3<bool>;
+
+    fn threshold_mean(&self) -> Result<Self::Output, Error> {
+        if self.shape()[2] > 1 {
+            Err(Error::ChannelDimensionMismatch)
+        } else {
+            let value = calculate_threshold_mean(&self)?;
+            let mask = apply_threshold(self, value);
+            Ok(mask)
+        }
+    }
+}
+
+fn calculate_threshold_mean<T>(array: &Array3<T>) -> Result<f64, Error>
+where
+    T: Copy + Clone + Num + NumAssignOps + ToPrimitive + FromPrimitive 
+{
+    Ok(array.sum().to_f64().unwrap() / array.len() as f64)
+}
+
+
+fn apply_threshold<T>(data: &Array3<T>, threshold: f64) -> Array3<bool>
+where
+    T: Copy + Clone + Num + NumAssignOps + ToPrimitive + FromPrimitive,
+{
+    let result = data.mapv(|x| x.to_f64().unwrap() >= threshold);
+    result
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ndarray::arr3;
+
+    #[test]
+    fn threshold_apply_threshold() {
+        let data = arr3(&[
+            [[0.2], [0.4], [0.0]],
+            [[0.7], [0.5], [0.8]],
+            [[0.1], [0.6], [0.0]],
+        ]);
+
+        let expected = arr3(&[
+            [[false], [false], [false]],
+            [[true], [true], [true]],
+            [[false], [true], [false]],
+        ]);
+
+        let result = apply_threshold(&data, 0.5);
+
+        assert_eq!(result, expected);
+    }
+
+    #[test]
+    fn threshold_calculate_threshold_otsu_ints() {
+        let data = arr3(&[
+            [[2], [4], [0]],
+            [[7], [5], [8]],
+            [[1], [6], [0]],
+        ]);
+        let result = calculate_threshold_otsu(&data).unwrap();
+        println!("Done {}", result);
+
+        // Calculated using Python's skimage.filters.threshold_otsu 
+        // on int input array. Float array returns 2.0156... 
+        let expected = 2.0;
+
+        assert_approx_eq!(result, expected, 5e-1);
+    }
+
+    #[test]
+    fn threshold_calculate_threshold_otsu_floats() {
+        let data = arr3(&[
+            [[n64(2.0)], [n64(4.0)], [n64(0.0)]],
+            [[n64(7.0)], [n64(5.0)], [n64(8.0)]],
+            [[n64(1.0)], [n64(6.0)], [n64(0.0)]],
+        ]);
+
+        let result = calculate_threshold_otsu(&data).unwrap();
+
+        // Calculated using Python's skimage.filters.threshold_otsu 
+        // on int input array. Float array returns 2.0156... 
+        let expected = 2.0156;
+
+        assert_approx_eq!(result, expected, 5e-1);
+    }
+
+    #[test]
+    fn threshold_calculate_threshold_mean_ints() {
+        let data = arr3(&[
+            [[4], [4], [4]],
+            [[5], [5], [5]],
+            [[6], [6], [6]],
+        ]);
+
+        let result = calculate_threshold_mean(&data).unwrap();
+        let expected = 5.0;
+
+        assert_approx_eq!(result, expected, 1e-16);
+    }
+
+    #[test]
+    fn threshold_calculate_threshold_mean_floats() {
+        let data = arr3(&[
+            [[4.0], [4.0], [4.0]],
+            [[5.0], [5.0], [5.0]],
+            [[6.0], [6.0], [6.0]],
+        ]);
+
+        let result = calculate_threshold_mean(&data).unwrap();
+        let expected = 5.0;
+
+        assert_approx_eq!(result, expected, 1e-16);
+    }
+}