candle/candle-examples/src/object_detection.rs

/// A bounding box around an object.
#[derive(Debug, Clone)]
pub struct Bbox {
    pub xmin: f32,
    pub ymin: f32,
    pub xmax: f32,
    pub ymax: f32,
    pub confidence: f32,
    pub keypoints: Vec<KeyPoint>,
}

#[derive(Debug, Clone, Copy, PartialEq)]
pub struct KeyPoint {
    pub x: f32,
    pub y: f32,
    pub mask: f32,
}

/// Intersection over union of two bounding boxes.
pub fn iou(b1: &Bbox, b2: &Bbox) -> f32 {
    let b1_area = (b1.xmax - b1.xmin + 1.) * (b1.ymax - b1.ymin + 1.);
    let b2_area = (b2.xmax - b2.xmin + 1.) * (b2.ymax - b2.ymin + 1.);
    let i_xmin = b1.xmin.max(b2.xmin);
    let i_xmax = b1.xmax.min(b2.xmax);
    let i_ymin = b1.ymin.max(b2.ymin);
    let i_ymax = b1.ymax.min(b2.ymax);
    let i_area = (i_xmax - i_xmin + 1.).max(0.) * (i_ymax - i_ymin + 1.).max(0.);
    i_area / (b1_area + b2_area - i_area)
}

pub fn non_maximum_suppression(bboxes: &mut [Vec<Bbox>], threshold: f32) {
    // Perform non-maximum suppression.
    for bboxes_for_class in bboxes.iter_mut() {
        bboxes_for_class.sort_by(|b1, b2| b2.confidence.partial_cmp(&b1.confidence).unwrap());
        let mut current_index = 0;
        for index in 0..bboxes_for_class.len() {
            let mut drop = false;
            for prev_index in 0..current_index {
                let iou = iou(&bboxes_for_class[prev_index], &bboxes_for_class[index]);
                if iou > threshold {
                    drop = true;
                    break;
                }
            }
            if !drop {
                bboxes_for_class.swap(current_index, index);
                current_index += 1;
            }
        }
        bboxes_for_class.truncate(current_index);
    }
}