Export JPG with AVM (WCS metadata) by bmorris3 · Pull Request #4065 · spacetelescope/jdaviz

bmorris3 · 2026-03-04T22:18:48Z

Description

The main goal of this PR is to allow users to export a screenshot of their image viewer and load that screenshot into aladin-lite or mast-aladin. In order to overlay the screenshot on the correct sky coordinates in aladin-lite, the screenshot must contain AVM.

AVM is a metadata standard for embedding WCS in common image formats, including PNG and JPG. The python module for embedding AVM from WCS is pyavm by @astrofrog, which is a new (and extremely minimal) dependency in this PR.

This PR adds a supported image viewer screenshot filetype ("jpg"). When selected, the Export plugin:

exports a PNG as normal
assembles WCS for the screenshot
converts PNG to JPG using PIL, since PNG w/ AVM isn't yet supported by aladin-lite
embeds the WCS into the final JPG, and cleans up temporary files

The result is a JPG file with AVM. You can check this by calling:

$ head imviz-0.jpg
��JFIF��^http://ns.adobe.com/xap/1.0/<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?> <x:xmpmeta xmlns:avm="http://www.communicatingastronomy.org/avm/1.0/" xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:x="adobe:ns:meta/"><rdf:RDF><rdf:Description><avm:MetadataVersion>1.1000000000000001</avm:MetadataVersion><photoshop:Source>jdaviz</photoshop:Source<avm:Spatial.CoordinateFrame>FK5</avm:Spatial.CoordinateFrame><avm:Spatial.Equinox>2000.0013661202186</avm:Spatial.Equinox><avm:Spatial.ReferenceValue><rdf:Seq><rdf:li>201.7042659999999898</rdf:li>...

See that madness? That's the WCS.

Now you can load the JPG with aladin-lite in your browser, or in an instance of mast-aladin. In either environment, right click* on the sky , select "Load a local file" > "FITS image"*, and select the imviz-0.jpg file (*see known issues below).

To try this out in a notebook with mast-aladin, run the following in one cell:

from mast_aladin import AppSidecar
import astropy.units as u
from astropy.coordinates import SkyCoord

# open mast-aladin and jdaviz
ma, viz = AppSidecar.open(anchor=['split-bottom', 'split-right'])
target = SkyCoord(ra=201.704266 * u.deg, dec=-47.44637979 * u.deg)
fov = 36 * u.arcsec

# set up the mast-aladin viewport
ma.target = target
ma.fov = fov
ma.survey = 'HST/color'

viz.load('mast:jwst/products/jw01478-o014_t003_nircam_clear-f115w_i2d.fits', format='Image')
viz.link_data('wcs')
viz.default_viewer.reset_limits()

# configure the colormap
plot_opts = viz.plugins['Plot Options']
plot_opts.image_colormap = 'viridis'
plot_opts.stretch_vmin = 5
plot_opts.stretch_vmax  = 1000
plot_opts.stretch_function = 'Arcsinh'

# set the jdaviz viewport to match mast-aladin
viz.default_viewer._obj.glue_viewer.aid.set_viewport(
    center=target,
    fov=fov
)

and in a second cell:

# export JPG with AVM
export = viz.plugins['Export']
export.viewer_format = 'jpg'
export.export(overwrite=True)

You will see this:

jdaviz-to-aladin-export-720.mov

Known issues

aladin-lite will happily load a JPG via the "load a local file > FITS image" button. This may be addressed by CDS soon: Feature request: export screenshots with AVM cds-astro/aladin-lite#349 (comment)
aladin-lite on OS X and in Chrome doesn't support ctrl+click to open the menu shown in this demo. This is a known issue that will be resolved shortly. Workaround: aladin-lite does recognize ctrl+click on OS X in Firefox. bug: right-click on HiPS opens menu in firefox but not chrome cds-astro/aladin-lite#348 (comment)
the WCS that I'm constructing for the screenshot underestimates the pixel scale. I haven't found the source of this yet.
aladin-lite cannot read PNG with AVM yet, though the idea was received positively in Feature request: export screenshots with AVM cds-astro/aladin-lite#349. If PNG+AVM support becomes available, I will replicate the AVM logic for exporting PNGs as well. One major advantage to PNG is that it supports transparency, so we could export screenshots where out-of-bounds portions of the image are transparent, rather than a black background.

To do items before merge:

I haven't accounted for jdaviz users beginning in any orientation other than Default Orientation
should add logic to ensure that tmp files are removed if the export fails out early (prevent leaving tmp files)

Change log entry

Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
Do the proposed changes follow the STScI Style Guides?
Are tests added/updated as required? If so, do they follow the STScI Style Guides?
Are docs added/updated as required? If so, do they follow the STScI Style Guides?
If new remote data is added that uses MAST, is the URI added to the cache-download.yml workflow?
Did the CI pass? If not, are the failures related?
Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone. Bugfix milestone also needs an accompanying backport label.
After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

codecov · 2026-03-10T16:46:19Z

Codecov Report

❌ Patch coverage is 33.33333% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.51%. Comparing base (20e3eaa) to head (44d8dbf).

Files with missing lines	Patch %	Lines
jdaviz/configs/default/plugins/export/avm.py	24.00%	19 Missing ⚠️
jdaviz/configs/default/plugins/export/export.py	41.66%	7 Missing ⚠️

❌ Your patch check has failed because the patch coverage (33.33%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4065      +/-   ##
==========================================
- Coverage   84.60%   84.51%   -0.10%     
==========================================
  Files         202      203       +1     
  Lines       29402    29436      +34     
==========================================
+ Hits        24876    24878       +2     
- Misses       4526     4558      +32

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astrofrog · 2026-03-12T12:51:59Z

@bmorris3 - just FYI I released pyavm 0.9.9 today which fixes a few bugs. I don't suspect these were affecting you here, but let me know if you have any issues with this new version.

bmorris3 · 2026-03-12T14:23:37Z

Thank you @astrofrog!

kecnry · 2026-03-17T17:15:17Z

            output file already exists. Otherwise, a message will be sent
            to application snackbar instead.
+
+        embed_avm : bool


would there be any harm to having this on by default (or not even have the option to turn it off)?

I don't think there's any harm. I think we should preserve the option to turn it off, just in case there's ever an upstream bug.

I guess the downside is that it might be confusing for non-supported filetypes if the user passes this as true (or leaves it at the default) and we don't have checking that raises an error 🤔

kecnry · 2026-03-17T17:16:04Z

+
+                try:
+                    # export PNG
+                    tmp_filename = Path(str(Path(filename)).replace('.jpg', '.png'))


can this be done by writing to a buffer instead of a temporary file to disk?

I think pyavm is built around a file on disk, see for example: https://github.com/astrofrog/pyavm/blob/9152f6809426b40647ecbaefcefceabe09236d94/pyavm/jpeg.py#L64-L66

Is that right @astrofrog?

astrofrog · 2026-03-17T18:17:27Z

Is there any reason not to allow PNG export already as other tools may be able to use them?

Co-authored-by: Kyle Conroy <kyleconroy@gmail.com>

pcuste1

Pulled this PR down locally and it is working as advertised. As noted, it hasn't been designed with rotation in mind, and it handles at bit weird once the imviz viewer is rotated. This is likely in part due to the missing alpha channel and the change in FOV caused by rotation. We'll want to look further into this in a future PR. I'm also curious how it will handle projection once we introduce the feature to update that into jdaviz. Preliminary tests also show that WCS near the poles are handled properly as well

github-actions Bot added the plugin Label for plugins common to multiple configurations label Mar 4, 2026

bmorris3 mentioned this pull request Mar 5, 2026

Feature request: export screenshots with AVM cds-astro/aladin-lite#349

Open

bmorris3 added 5 commits March 10, 2026 11:39

fix for AIDA get viewport with GWCS

0f55a9e

adding pyavm

15e4cda

in progress

a2c3cfb

export jpg with AVM

d65d260

export to PNG with AVM

270a752

bmorris3 force-pushed the support-avm branch from 0da5224 to 270a752 Compare March 10, 2026 15:40

bmorris3 marked this pull request as ready for review March 10, 2026 15:40

bmorris3 requested review from MatthewPortman, cshanahan1, gibsongreen, haticekaratay, javerbukh, kecnry and rosteen as code owners March 10, 2026 15:40

bmorris3 added this to the 4.6 milestone Mar 10, 2026

codestyle fixes, changelog

44d8dbf

kecnry reviewed Mar 17, 2026

View reviewed changes

Update jdaviz/configs/default/plugins/export/export.py

58b876f

Co-authored-by: Kyle Conroy <kyleconroy@gmail.com>

pcuste1 approved these changes Apr 7, 2026

View reviewed changes

rosteen modified the milestones: 4.6, 5.1 Apr 15, 2026

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Export JPG with AVM (WCS metadata)#4065

Export JPG with AVM (WCS metadata)#4065
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Description

Known issues

To do items before merge:

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