Question: Possible to determine if an image is tiled?

[AntiSol]

Hi, thanks for pyvips, I've just started using it for a project and it's working great.

Is there a way to get information about the file I've loaded (e.g image format and importantly whether it's tiled) using pyvips? I've been messing around and looking through the docs but I haven't found what I'm looking for.

I am dealing with large (in the realm 40k x 40k) images in my project, but I'm only working with relatively small regions in these images, so when dealing with tiled tiff images pyvips is giving me really excellent performance, orders of magnitude faster than the old imagemagick code it's replacing. Much much faster than e.g jpeg.

Due to the advantage of tiled tiff, I'd like to have a feature in my software to detect if a user-provided image is a tiled tiff and offer to automatically convert it if it isn't.

I've written a 'convert to tiled tiff' method which saves my files in a format optimal for processing and this works well, but I can't seem to find any way to determine whether a file the user has provided is a tiled tiff or not.

I think I could perhaps use tiffload rather than Image.new_from_file, but I'd like my users to be able to easily load any image type supported by vips, so that's not ideal.

Does pyvips have any way to figure this out? I've been looking at Image.sequential, it seems like this is close to what I want, but it seems that open any file in random mode, e.g a jpeg. I also had a look at the output from .get_fields, but there doesn't seem to be much there that's helpful to me. Does pyvips have any way of figuring out what I want to know?

Any tips you have would be great. Thanks very much for your time :)

[jcupitt]

Hi @AntiSol,

I think this should work:

#!/usr/bin/python3

import sys
import pyvips

x = pyvips.Image.new_from_file(sys.argv[1], access="sequential")

if x.get_typeof("vips-sequential") != 0:
    print("sequential image")

If an image supports true random access, then opening it in seq mode will still give you a random access image. I see:

$ ~/try/access.py k2.jpg
sequential image
$ vips copy k2.jpg x.tif[tile]
$ ~/try/access.py x.tif
$

This will work for things like binary PPM too, not just tiled TIFF.

[AntiSol]

hi @jcupitt, awesome! this looks like exactly what I need! thanks so much! and thanks also for the super-fast response!

[AntiSol]

Hi @jcupitt

Sorry to bother you, but it looks like something has changed with a (somewhat) recent update.

I've been checking if x.get_typeof("vips-sequential") == 0 after opening with access="sequential"to see if an image is tiled, and this has been working fine, but since updating today (to vips-8.17.1), get_typeof("vips-sequential") is now returning 24 for the images that I've saved in a tiled tiff format.

I assume something has changed here? Are there docs for what these values are? I had a bit of a look but didn't find much.

If it helps, here's an example image that I've optimised and saved as a tiled tiff:
deepfield_hubble_orion.optimised.tiff

[jcupitt]

Hello again, libvips 8.18 (out fairly soon) adds a new feature that lets you see the cache geometry of any loaded image:

libvips/libvips#4637

It should be a lot safer than checking sequential.

You're right, 8.17.1 is showing seq for random-access images, I'll have a look.

[jcupitt]

This is off topic, but did you see vipsdisp?

https://github.com/jcupitt/vipsdisp

It's a gtk4 image viewer I did that uses libvips to fetch image tiles. It keeps a sparse pyramid of asynchronously computed tiles as textures on your GPU and composites the visible set to the screen at 60fps as you pan and zoom. It's on flathub, brew and as a win binary, so it should be easy to test.

I don't know if that would fit at all with your stack, but there might at least be ideas you could reuse. If you're using gtk4, the viewer has an imagedisplay widget you ought to be able to just copy-paste into your code.

[AntiSol]

I hadn't seen vipsdisp. It looks like a pretty handy tool for dealing with large images! I'll definitely check it out.

But I'm afraid it doesn't help much for this issue, I'm a) using python and b) not using gtk4 (I've abandoned gtk due to their disregard for backwards compatibility). The project this is for isn't even a gui (https://gitlab.com/AntiSol/awpgen2)

I had a look at the PR you linked to and it looks promising. If I understand correctly once this is applied, it won't have the tile-width and tile-height fields for images which aren't tiled, so I think an appropriate test to see if I'm looking at a tiled would be: if 'tile-width' in image.get_fields(), right? I think doing .get('tile-width') would raise an error for a non-tiled image.

I'll probably also need to check the vips version for a little while so that I'm able to support older versions too.

I'll look forward to hearing back on what's going on with vips-sequential. Thanks! 👍

[jcupitt]

It looks like this was changed a while ago:

libvips/libvips@907d17c

I think we had to change the behaviour to fix a caching issue, sorry. Testing sequential will work in libvips 8.12, but stopped working in 8.13.

I can't think of a libvips workaround for this :( I think you'll need to run tiffinfo and look at the output, perhaps:

$ tiffinfo x.tif | grep "Tile Width"
  Tile Width: 128 Tile Length: 128

[AntiSol]

argh, annoying. running a thirdparty program is very not optimal. Maybe I'll try downgrading back to 8.12