utils.py

import numpy as np
import cv2
import torch
import time
import torchvision
import random


def box_iou(box1, box2):
    # https://github.com/pytorch/vision/blob/master/torchvision/ops/boxes.py
    """
    Return intersection-over-union (Jaccard index) of boxes.
    Both sets of boxes are expected to be in (x1, y1, x2, y2) format.
    Arguments:
        box1 (Tensor[N, 4])
        box2 (Tensor[M, 4])
    Returns:
        iou (Tensor[N, M]): the NxM matrix containing the pairwise
            IoU values for every element in boxes1 and boxes2
    """

    def box_area(box):
        # box = 4xn
        return (box[2] - box[0]) * (box[3] - box[1])

    area1 = box_area(box1.T)
    area2 = box_area(box2.T)

    # inter(N,M) = (rb(N,M,2) - lt(N,M,2)).clamp(0).prod(2)
    inter = (torch.min(box1[:, None, 2:], box2[:, 2:]) - torch.max(box1[:, None, :2], box2[:, :2])).clamp(0).prod(2)
    return inter / (area1[:, None] + area2 - inter)  # iou = inter / (area1 + area2 - inter)


def plot_one_box(x, image, color=None, label=None, line_thickness=None):
    # Plots one bounding box on image img
    tl = line_thickness or round(
        0.002 * (image.shape[0] + image.shape[1]) / 2) + 1  # line/font thickness
    color = color or [random.randint(0, 255) for _ in range(3)]
    c1, c2 = (int(x[0]), int(x[1])), (int(x[2]), int(x[3]))
    cv2.rectangle(image, c1, c2, color, thickness=tl, lineType=cv2.LINE_AA)
    if label:
        tf = max(tl - 1, 1)  # font thickness
        t_size = cv2.getTextSize(label, 0, fontScale=tl / 3, thickness=tf)[0]
        c2 = c1[0] + t_size[0], c1[1] - t_size[1] - 3
        cv2.rectangle(image, c1, c2, color, -1, cv2.LINE_AA)  # filled
        cv2.putText(image, label, (c1[0], c1[1] - 2), 0, tl / 3,
                    [225, 255, 255], thickness=tf, lineType=cv2.LINE_AA)


def clip_coords(boxes, img_shape):
    # Clip bounding xyxy bounding boxes to image shape (height, width)
    boxes[:, 0].clamp_(0, img_shape[1])  # x1
    boxes[:, 1].clamp_(0, img_shape[0])  # y1
    boxes[:, 2].clamp_(0, img_shape[1])  # x2
    boxes[:, 3].clamp_(0, img_shape[0])  # y2


def scale_coords(img1_shape, coords, img0_shape, ratio_pad=None):
    # Rescale coords (xyxy) from img1_shape to img0_shape
    if ratio_pad is None:  # calculate from img0_shape
        gain = max(img1_shape) / max(img0_shape)  # gain  = old / new
        pad = (img1_shape[1] - img0_shape[1] * gain) / \
              2, (img1_shape[0] - img0_shape[0] * gain) / 2  # wh padding
    else:
        gain = ratio_pad[0][0]
        pad = ratio_pad[1]

    coords[:, [0, 2]] -= pad[0]  # x padding
    coords[:, [1, 3]] -= pad[1]  # y padding
    coords[:, :4] /= gain
    clip_coords(coords, img0_shape)
    return coords


def xywh2xyxy(x):
    # Convert nx4 boxes from [x, y, w, h] to [x1, y1, x2, y2] where
    # xy1=top-left, xy2=bottom-right
    y = torch.zeros_like(x) if isinstance(
        x, torch.Tensor) else np.zeros_like(x)
    y[:, 0] = x[:, 0] - x[:, 2] / 2  # top left x
    y[:, 1] = x[:, 1] - x[:, 3] / 2  # top left y
    y[:, 2] = x[:, 0] + x[:, 2] / 2  # bottom right x
    y[:, 3] = x[:, 1] + x[:, 3] / 2  # bottom right y
    return y


def letterbox(img, new_shape=(416, 416), color=(114, 114, 114), auto=True,
              scaleFill=False, scaleup=True):
    # Resize image to a 32-pixel-multiple rectangle
    # https://github.com/ultralytics/yolov3/issues/232
    shape = img.shape[:2]  # current shape [height, width]
    if isinstance(new_shape, int):
        new_shape = (new_shape, new_shape)

    # Scale ratio (new / old)
    r = min(new_shape[0] / shape[0], new_shape[1] / shape[1])
    if not scaleup:  # only scale down, do not scale up (for better test mAP)
        r = min(r, 1.0)

    # Compute padding
    ratio = r, r  # width, height ratios
    new_unpad = int(round(shape[1] * r)), int(round(shape[0] * r))
    dw, dh = new_shape[1] - new_unpad[0], new_shape[0] - \
             new_unpad[1]  # wh padding
    if auto:  # minimum rectangle
        dw, dh = np.mod(dw, 32), np.mod(dh, 32)  # wh padding
    elif scaleFill:  # stretch
        dw, dh = 0.0, 0.0
        new_unpad = new_shape
        ratio = new_shape[0] / shape[1], new_shape[1] / \
                shape[0]  # width, height ratios

    dw /= 2  # divide padding into 2 sides
    dh /= 2

    if shape[::-1] != new_unpad:  # resize
        img = cv2.resize(img, new_unpad, interpolation=cv2.INTER_LINEAR)
    top, bottom = int(round(dh - 0.1)), int(round(dh + 0.1))
    left, right = int(round(dw - 0.1)), int(round(dw + 0.1))
    img = cv2.copyMakeBorder(img, top, bottom, left, right,
                             cv2.BORDER_CONSTANT, value=color)  # add border
    return img, ratio, (dw, dh)


def non_max_suppression(
        prediction,
        conf_thres=0.1,
        iou_thres=0.6,
        multi_label=True,
        classes=None,
        agnostic=False):
    """
    Performs  Non-Maximum Suppression on inference results
    Returns detections with shape:
        nx6 (x1, y1, x2, y2, conf, cls)
    """

    # Settings
    merge = True  # merge for best mAP
    # (pixels) minimum and maximum box width and height
    min_wh, max_wh = 2, 4096
    time_limit = 10.0  # seconds to quit after

    t = time.time()
    nc = prediction[0].shape[1] - 5  # number of classes
    multi_label &= nc > 1  # multiple labels per box
    output = [None] * prediction.shape[0]
    for xi, x in enumerate(prediction):  # image index, image inference
        # Apply constraints
        x = x[x[:, 4] > conf_thres]  # confidence
        x = x[((x[:, 2:4] > min_wh) & (x[:, 2:4] < max_wh)).all(1)]

        # If none remain process next image
        if not x.shape[0]:
            continue

        # Compute conf
        x[..., 5:] *= x[..., 4:5]  # conf = obj_conf * cls_conf

        # Box (center x, center y, width, height) to (x1, y1, x2, y2)
        box = xywh2xyxy(x[:, :4])

        # Detections matrix nx6 (xyxy, conf, cls)
        if multi_label:
            i, j = (x[:, 5:] > conf_thres).nonzero().t()
            x = torch.cat((box[i], x[i, j + 5].unsqueeze(1),
                           j.float().unsqueeze(1)), 1)
        else:  # best class only
            conf, j = x[:, 5:].max(1)
            x = torch.cat(
                (box, conf.unsqueeze(1), j.float().unsqueeze(1)), 1)[
                conf > conf_thres]

        # Filter by class
        if classes:
            x = x[(j.view(-1, 1) == torch.tensor(classes,
                                                 device=j.device)).any(1)]

        # Apply finite constraint
        # if not torch.isfinite(x).all():
        #     x = x[torch.isfinite(x).all(1)]

        # If none remain process next image
        n = x.shape[0]  # number of boxes
        if not n:
            continue

        # Sort by confidence
        # x = x[x[:, 4].argsort(descending=True)]

        # Batched NMS
        c = x[:, 5] * 0 if agnostic else x[:, 5]  # classes
        boxes, scores = x[:, :4].clone() + c.view(-1, 1) * \
                        max_wh, x[:, 4]  # boxes (offset by class), scores
        i = torchvision.ops.boxes.nms(boxes, scores, iou_thres)
        if merge and (
                1 < n < 3E3):  # Merge NMS (boxes merged using weighted mean)
            try:  # update boxes as boxes(i,4) = weights(i,n) * boxes(n,4)
                iou = box_iou(boxes[i], boxes) > iou_thres  # iou matrix
                weights = iou * scores[None]  # box weights
                x[i, :4] = torch.mm(weights, x[:, :4]).float(
                ) / weights.sum(1, keepdim=True)  # merged boxes
                # i = i[iou.sum(1) > 1]  # require redundancy
            except BaseException:
                # https://github.com/ultralytics/yolov3/issues/1139
                # print(x, i, x.shape, i.shape)
                pass

        output[xi] = x[i]
        if (time.time() - t) > time_limit:
            break  # time limit exceeded

    return output