catimg

#!/usr/bin/env python3
import argparse

helpmsg = ''.join((
    "Concatenate images along a specified dimension. ",
    "If no dimensions are specified (-x/-y), then the first unequal ",
    "dimension is used. If neither dimension has equal size, then ",
    "the Y dimension is used."
))
parser = argparse.ArgumentParser(
    description=helpmsg)
parser.add_argument('-x', action="store_true", help="Concatenate along X")
parser.add_argument('-y', action="store_true", help="Concatenate along Y")
parser.add_argument('-m', '--mode', nargs=1, metavar='MODE')
parser.add_argument('-b', '--border', nargs=2, metavar=('width', 'color'))
parser.add_argument('-o', '--output', required=True, help="Name of concatenated output file")
parser.add_argument('filename', nargs='+', help="Images to concatenate")

args = parser.parse_args()

img_mode = args.mode and args.mode[0]

from PIL import Image
import numpy as np

images = []
for filename in args.filename:
    im = Image.open(filename)
    if img_mode: im = im.convert(mode=img_mode)
    else: img_mode = im.mode
    im = np.asarray(im)
    images.append(im)

shape = images[0].shape
equal = [True, True]
for image in images[1:]:
    # determine which dimensions match
    for dim, s in enumerate(image.shape[:2]):
        ed = equal[dim]
        sd = shape[dim]
        equal[dim] = ed and (sd == s)

# if user chose a dimension, use it
if args.x:
    dim = 0
elif args.y:
    dim = 1
# otherwise, choose the first equivalent dimension, or Y
elif equal[1] and not equal[0]:
    dim = 0
else:
    dim = 1

if args.border:
    width, color = args.border
    width = int(width)
    height = shape[abs(dim-1)]
    border_shape = [height, width]
    if dim: border_shape.reverse()
    border = Image.new(img_mode, border_shape, color=color)
    border = np.asarray(border)
    for i in reversed(range(1, len(images))):
        images.insert(i, border)

# do the actual concatenation along the specified dimension
output = np.concatenate(images, axis=dim)
output = Image.fromarray(output)
output.save(args.output)