imgUtils.py

#!/usr/bin/env python

import cv2

def scaleW(img, newWidthPx=640):
    ''' Scale image img to have a new width newWidthPx pixels, retaining the 
        image aspect ratio.
        Returns a new opencv image.
    '''
    h, w, c = img.shape
    #print("initial w,h=%d,%d" % (w,h))
    wNew = newWidthPx
    hNew = int(h*wNew/w)
    #print("new w,h=%d,%d" % (wNew, hNew))
    imgScaled = cv2.resize(img, (wNew, hNew))
    return(imgScaled)

# LetterBox class from ultralytics augment.py github.com/ultralytics/ultralytics/yolo/data/augment.py
class LetterBox:
    """Resize image and padding for detection, instance segmentation, pose."""

    def __init__(self, new_shape=(640, 640), auto=False, scaleFill=False, scaleup=True, stride=32):
        """Initialize LetterBox object with specific parameters."""
        self.new_shape = new_shape
        self.auto = auto
        self.scaleFill = scaleFill
        self.scaleup = scaleup
        self.stride = stride

    def __call__(self, labels=None, image=None):
        """Return updated labels and image with added border."""
        if labels is None:
            labels = {}
        img = labels.get('img') if image is None else image
        shape = img.shape[:2]  # current shape [height, width]
        new_shape = labels.pop('rect_shape', self.new_shape)
        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 self.scaleup:  # only scale down, do not scale up (for better val 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 self.auto:  # minimum rectangle
            dw, dh = np.mod(dw, self.stride), np.mod(dh, self.stride)  # wh padding
        elif self.scaleFill:  # stretch
            dw, dh = 0.0, 0.0
            new_unpad = (new_shape[1], new_shape[0])
            ratio = new_shape[1] / shape[1], new_shape[0] / shape[0]  # width, height ratios

        dw /= 2  # divide padding into 2 sides
        dh /= 2
        if labels.get('ratio_pad'):
            labels['ratio_pad'] = (labels['ratio_pad'], (dw, dh))  # for evaluation

        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=(114, 114, 114))  # add border

        if len(labels):
            labels = self._update_labels(labels, ratio, dw, dh)
            labels['img'] = img
            labels['resized_shape'] = new_shape
            return labels
        else:
            return img

    def _update_labels(self, labels, ratio, padw, padh):
        """Update labels."""
        labels['instances'].convert_bbox(format='xyxy')
        labels['instances'].denormalize(*labels['img'].shape[:2][::-1])
        labels['instances'].scale(*ratio)
        labels['instances'].add_padding(padw, padh)
        return labels