Changes the scales down the image size and the corresponding bounding box.

shrink_images.py

import random
from re import S
import xml.etree.ElementTree as ET
from glob import glob
import cv2

input_dir ='/home/isaac/Desktop/work_area/working_on/'

files = glob(input_dir+'*.png')
# For each file with a .png extension
for file in files:

    scale_factor = random.randint(3,8)
    scale_factor = scale_factor/10
    print(scale_factor)
    # -------- PNG WORK -------- #
    img = cv2.imread(file,1)
    cv2.imshow('Original', img)

    # Scale the image by half
    img_half = cv2.resize(img, (0, 0), fx=scale_factor, fy=scale_factor)
    
    # Collect the scaled image dimensions
    x_dim = img_half.shape[0]
    y_dim = img_half.shape[1]

    # Save the image to the directory where it originated
    cv2.imwrite(file, img_half)

    # ------- XML WORK -------- #
    # Get the xml file name
    tmp_file = file.split(".")
    xml_file = tmp_file[0]+'.xml'
    # Open the xml file
    tree = ET.parse(xml_file)
    root = tree.getroot()
    bbox = root.find('object').find('bndbox')

    # Access the bounding box coordinates
    xmin = bbox.find('xmin')
    ymin = bbox.find('ymin')
    xmax = bbox.find('xmax')
    ymax = bbox.find('ymax')

    # Need to round down or up, cannot have half a pixel
    # Change to a string for the xml
    xmin.text = str(round(int(xmin.text)*scale_factor))
    ymin.text = str(round(int(ymin.text)*scale_factor))
    xmax.text = str(round(int(xmax.text)*scale_factor))
    ymax.text = str(round(int(ymax.text)*scale_factor))

    # Access the image dimensions 
    width = root.find('size').find('width')
    height = root.find('size').find('height')

    # Change the image dimensions in the xml file
    width.text = str(x_dim)
    height.text = str(y_dim)

    # Save the changes to the xml file
    tree.write(xml_file)