Delta E

[joshqsumner]

Describe your changes
Adds delta E calculation as part of color card detection and as a standalone function in plantcv.plantcv.transform. The main function is kept as a helper in transform which is called by a user-facing function with the intent of being used on calibrated images to show a calibrated difference from the expectation and is called by detect_color_card with the intent of showing the starting difference.

Type of update
This is a new feature.

Associated issues
Closes #1770

Additional context
Currently this only compares against expected values for color chips, we could have something where you give it one image, run the correction, then compare the delta E raw vs corrected. I did it this way because I don't think it's as useful to say "the color correction changed the image" to X degree when we don't know if the change is good or bad so to speak. I'd like to hear argument against that if anyone has it. I think we could add that functionality in the piece I already wrote with some logic to handle if card_type is an image.

this also does not make a bar plot like the one from imageZebra but it could if we wanted that. There is an example in my last comment in #1770 about what that might look like.

For the reviewer
See this page for instructions on how to review the pull request.

• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[deepsource-io]

DeepSource Code Review

We reviewed changes in ce0b36e...8a6996b on this pull request. Below is the summary for the review, and you can see the individual issues we found as inline review comments.

See full review on DeepSource ↗

PR Report Card

Overall Grade

Security   Reliability   Complexity   Hygiene   Coverage

Code Review Summary

Analyzer	Status	Updated (UTC)	Details
Python		Jun 9, 2026 8:15p.m.	Review ↗
Code coverage		Jun 9, 2026 8:15p.m.	Review ↗

Code Coverage Summary

Language	Line Coverage (New Code)	Line Coverage (Overall)
Aggregate	100% [✓ above threshold]	99.9% [▼ down 0.1% from main]
Python	100% [✓ above threshold]	99.9% [▼ down 0.1% from main]

➟ Additional coverage metrics may have been reported. See full coverage report ↗

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[Copilot]

Pull request overview

This PR adds Delta E color-difference reporting for detected color cards, exposing a new pcv.transform.deltaE function and integrating automatic Delta E metadata generation into color-card detection.

Changes:

• Adds _delta_e calculation logic and exports user-facing deltaE.
• Updates detect_color_card to optionally compute Delta E metadata.
• Adds tests and documentation for the new Delta E workflow.

Reviewed changes

Copilot reviewed 8 out of 10 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
plantcv/plantcv/transform/delta_e.py	Adds Delta E computation, metadata output, and debug plotting.
plantcv/plantcv/transform/detect_color_card.py	Adds deltaE wrapper and automatic Delta E calculation option.
plantcv/plantcv/transform/__init__.py	Exports deltaE from the transform namespace.
tests/plantcv/transform/test_deltaE.py	Adds tests for Macbeth, Astro, and debug plotting behavior.
docs/transform_deltaE.md	Adds documentation page for Delta E usage.
docs/transform_detect_color_card.md	Updates color-card detection docs for Delta E metadata.
docs/updating.md	Records new/updated transform signatures.
mkdocs.yml	Adds Delta E documentation to navigation.

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