Example implementation of the python edge expansion approach

import cv2
 
# big_pad=True: edge padding when target image height and width are both larger than the original image
# big_pad=False: scale to the smallest scale of the target size before edge filling
# borderType=cv2.BORDER_CONSTANT: indicates constant fill, borderValue is fill constant 0~255 (black~white)
# borderType=cv2.BORDER_REPLICATE: Border Replication Fill
# borderType=cv2.BORDER_REFLECT: Border Reflection Fill
# borderType=cv2.BORDER_WRAP: Border Wrap Fill
 
def image_padding(image, target_shape, big_pad=True, 
                  borderType=cv2.BORDER_REFLECT, borderValue=(0, 0, 0)):
    # Target size size
    ph, pw = target_shape
    # Original image size
    h,  w, _ = 
    if big_pad and ph > h and pw > w: # Edge fill centered on the original image
        top = bottom = (ph - h) // 2  # Get the top and bottom fill sizes
        top += (ph - h) % 2 # To ensure target size, +1 if not divisible
        left = right = (pw - w) // 2
        left += (pw - w) % 2 # To ensure target size, ditto upper left + 1
        image_padded = (image, top, bottom, left, right,
                                          borderType=borderType, value=borderValue)
    else: # Minimum scaled fills (large sizes: larger changes in height/width ratios will be filled, small sizes vice versa)
        # Calculate image size after scaling
        scale = min(pw/w, ph/h) # Get the minimum ratio of height/width changes
        nw, nh = int(scale * w), int(scale * h)
        # Scale the original image to the smallest percentage of the target size
        img_resized = (image, (nw, nh))
        top = bottom = (ph - nh) // 2  # Get the top and bottom fill sizes
        top += (ph - nh) % 2 # To ensure target size, +1 if not divisible
        left = right = (pw - nw) // 2
        left += (pw - nw) % 2 # To ensure target size, ditto upper left + 1
        image_padded = (img_resized, top, bottom, left, right, 
                                          borderType=borderType, value=borderValue)
    return image_padded
 
 
if __name__ == "__main__":
    path = './2_2.png'
    img = (path)
    img_pad = image_padding(img, (640,640))
    ('./1_BORDER_WRAP.png',img_pad)
    # ('./1_.png',img_pad[64:576,64:576])