libvips has an arrayjoin operator that can join a set of tiles together into a large image.
You can use it like this (on the linux command-line):
vips arrayjoin "$(ls *.jpeg | sort -t_ -k2g -k1g)" x.tif[tile,pyramid,compression=jpeg] --across 20
That will load all the JPG image in the current directory, assemble them into a huge grid, 20 images across, and write as a TIFF pyramid. You'd need to check the size of your grid, obviously, and adjust the across parameter.
The $() part sorts the filenames of the form x_y.jpg by y first, then x, in numeric order. Without that, the tiles will be transposed, annoyingly.
That's assuming overlap 0. If your tiles have an overlap, you'll need to set the hspacing and vspacing options to control how tiles are positioned. For example:
vips arrayjoin "$(ls *.jpg | sort -t_ -k2g -k1g)" x.tif --across 20 --hspacing 254 --vspacing 254
Will position the tiles every 254 pixels horizontally and vertically.
arrayjoin has to be able to open all of the input images, so it needs a lot of file descriptors. Most linuxes default to a maximum of 1024 files open at once per process, so you'll probably need to raise that number. Usually you just edit a couple of config files and log out and in again. I set my system to 65536, but you can use any number.
Windows has a hard limit of 2000 files per process which you cannot change. You'll need to assemble in sections on that platform.
Here's a worked example. First, create a deepzoom pyramid with no overlaps:
john@kiwi:~/pics/x$ vips dzsave ~/pics/k2.jpg x --overlap 0
john@kiwi:~/pics/x$ cd x_files/11
john@kiwi:~/pics/x/x_files/11$ ls
0_0.jpeg 0_7.jpeg 1_5.jpeg 2_3.jpeg 3_1.jpeg 3_8.jpeg 4_6.jpeg 5_4.jpeg
0_1.jpeg 0_8.jpeg 1_6.jpeg 2_4.jpeg 3_2.jpeg 4_0.jpeg 4_7.jpeg 5_5.jpeg
0_2.jpeg 1_0.jpeg 1_7.jpeg 2_5.jpeg 3_3.jpeg 4_1.jpeg 4_8.jpeg 5_6.jpeg
0_3.jpeg 1_1.jpeg 1_8.jpeg 2_6.jpeg 3_4.jpeg 4_2.jpeg 5_0.jpeg 5_7.jpeg
0_4.jpeg 1_2.jpeg 2_0.jpeg 2_7.jpeg 3_5.jpeg 4_3.jpeg 5_1.jpeg 5_8.jpeg
0_5.jpeg 1_3.jpeg 2_1.jpeg 2_8.jpeg 3_6.jpeg 4_4.jpeg 5_2.jpeg
0_6.jpeg 1_4.jpeg 2_2.jpeg 3_0.jpeg 3_7.jpeg 4_5.jpeg 5_3.jpeg
You can see it's made a grid of tiles 6 across and 9 down.
Now reassemble the tiles and write as a TIFF pyramid:
john@kiwi:~/pics/x/x_files/11$ vips arrayjoin "$(ls *.jpeg | sort -t_ -k2g -k1g)" x.tif[tile,pyramid,compression=jpeg] --across 6
john@kiwi:~/pics/x/x_files/11$ vipsheader x.tif
x.tif: 1524x2286 uchar, 3 bands, srgb, tiffload_stream
With pyvips it would be something like:
#!/usr/bin/env python3
import pyvips
tiles_across = 142
tiles_down = 150
tiles = [pyvips.Image.new_from_file(f"{x}_{y}.jpeg", access="sequential")
for y in range(tiles_down) for x in range(tiles_across)]
im = pyvips.Image.arrayjoin(tiles, across=tiles_across)
im.write_to_file("x.jpg")
That took about 10 minutes and 6gb of ram to join 21,000 tiles on this laptop.
