What are minimal image dimensions allowed for find_trim?

[Nakilon]

# vips getpoint /tmp/t.v 0 0
123 123 123 
# vips find_trim /tmp/t.v --threshold 0 --background "123 123 123"
rank: window too large

# vipsheader -f width /tmp/t.v
2
# vipsheader -f height /tmp/t.v
17
# vips pngsave /tmp/t.v /tmp/temp.png
# xxd /tmp/temp.png 
00000000: 8950 4e47 0d0a 1a0a 0000 000d 4948 4452  .PNG........IHDR
00000010: 0000 0002 0000 0011 0802 0000 0078 96ea  .............x..
00000020: 4600 0000 0970 4859 7300 000b 1200 000b  F....pHYs.......
00000030: 1201 d2dd 7efc 0000 0049 4944 4154 0899  ....~....IIDAT..
00000040: 75cb a10d 4021 0c00 d1eb a73b 20d1 9d91  u...@!.....; ...
00000050: d9e8 0c75 354c 8201 4382 faea 9297 9cf4  ...u5L..C.......
00000060: de01 5d6b 011f 00c8 1803 90bd f7c3 9bd2  ..]k............
00000070: 5a8b 08cd cc87 6a66 7f83 ba3b 506a ad73  Z.....jf...;Pj.s
00000080: ce8b 07f7 2e17 99fe 5162 c300 0000 0049  ........Qb.....I
00000090: 454e 44ae 4260 82                        END.B`.

# vips -v
vips-8.7.2-Wed Dec  5 17:37:43 UTC 2018

[jcupitt]

Oh, interesting, I've never tried it on really small images.

It does a median filter, so 3x3 I think.

john@yingna ~/pics $ vips black x.v 3 3
john@yingna ~/pics $ vips find_trim x.v
0
0
3
3
john@yingna ~/pics $ vips black x.v 2 2
john@yingna ~/pics $ vips find_trim x.v
rank: window too large

[Nakilon]

Oh, thanks. Probably it needs to be mentioned in docs or better have a more clear error message.