String issue for Python multiprocessing

facing some issues with string parsing and the multiprocessing library. Here is my code, and I also outline the function calls and error.

def semi_func(tile):
        with open(tile, 'rb') as f:
           img = Image.open(BytesIO(f.read()))
           resized_im, seg_map = MODEL.run(img)
           vis_segmentation_tiles(str(tile),resized_im, seg_map)
           x = np.unique(seg_map)
           x = x.tolist()
           print("THIS IS X", x)
           ans_tiles[str(tile)] = x
           print(x)
        return ans_tiles
    
def split_tiles_new(image_path, tiledir):
        print("1")
        pool = Pool(processes=5)
        print("2")
        num_tiles = 9
        tiles = image_slicer.slice(image_path, num_tiles, save=False)
        print("3")
        print(tiles)
        image_slicer.save_tiles(tiles, directory=tiledir)
        print(tiles)
        print("TILES ABOEVE")
        
        onlytiles = [os.path.join(tiledir,f) for f in listdir(tiledir) if isfile(join(tiledir, f))]
       
        ans_tiles = {}
        print(onlytiles)
        onlytiles = list(map(str, onlytiles))
        for t in onlytiles:
            print(t)
        for tile in onlytiles:
            print(tile)
            pool.map(semi_func,tile)
        pool.close()
        pool.join()
        print(ans_tiles)
        return ans_tiles

Here's what I'm feeding in terms of my functions:

ans_tiles = split_tiles_new(local_jpg, tiledir)

local_jpg = 'wheat044146108.jpg'

tiledir = 'tiles044146108'

Inside tiledir (the directory), there's a bunch of tiled images:

['tiles044146108/_03_02.png', 'tiles044146108/_03_01.png', 'tiles044146108/_02_02.png', 'tiles044146108/_01_01.png', 'tiles044146108/_03_03.png', 'tiles044146108/_01_02.png', 'tiles044146108/_02_01.png', 'tiles044146108/_02_03.png', 'tiles044146108/_01_03.png']

That's what is in the variable 'onlytiles'.

But my issue is this error:

multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/usr/lib/python3.7/multiprocessing/pool.py", line 121, in worker
    result = (True, func(*args, **kwds))
  File "/usr/lib/python3.7/multiprocessing/pool.py", line 44, in mapstar
    return list(map(*args))
  File "serve_wh.py", line 128, in semi_func
    with open(tile, 'rb') as f:
FileNotFoundError: [Errno 2] No such file or directory: 't'
"""

I am not sure why it is doing further slicing of the string? Any idea what I can do to ensure it just grabs each file from 'onlyfiles' list separately in this?