Ability to Customise Annotation Label Font Size in Swift Integration

[aliceedwards-ultralytics]

Currently, the Swift implementation of the Ultralytics annotation and inference engine does not provide a way to adjust the font size of annotation labels. This limitation makes it difficult to visualise and distinguish multiple annotations within dense scenes, especially when objects overlap.

There was previously functionality allowing font size adjustments, but this no longer appears to have an effect after transitioning to the current Ultralytics annotation engine. Review of the relevant plotting utilities (e.g., Plot.swift) shows no available parameter for controlling font size.

Impact:

• Reduced visual clarity when displaying a high number of annotations in a single frame.
• Inability to tailor UI presentation for specific use cases or display densities.
• Developers may need to fork and modify internal code to achieve the desired visualisation behaviour.

[UltralyticsAssistant]

👋 Hello @aliceedwards-ultralytics, thank you for submitting a ultralytics/yolo-ios-app 🚀 Issue. This is an automated response, and an Ultralytics engineer will also assist you here soon.

To help us address your concern efficiently, please ensure you've provided the following information:

1. For bug reports:

   • A clear and concise description of the bug and when it occurs (e.g., during live inference, when rendering frames, etc.)
   • A minimum reproducible example MRE that demonstrates the issue (ideally a small Swift snippet or sample project)
   • Your environment details (iOS version, device model or simulator, Xcode version, Swift version, and the yolo-ios-app commit/branch)
   • Expected behavior vs. actual behavior (e.g., desired font scaling vs. current rendering)
   • Any relevant logs, console output, or screenshots/videos illustrating the issue

2. For feature requests:

   • A clear and concise description of the proposed feature
   • The problem this feature would solve and why it’s important for your workflow
   • Any alternative solutions or workarounds you’ve considered

3. For questions:

   • Provide as much context as possible about your question
   • Include any research you’ve already done on the topic
   • Specify which parts of the documentation, if any, you’ve already consulted

Please make sure you've searched existing issues to avoid duplicates. If you need to add any additional information, please comment on this issue. 🙏

Thank you for your contribution to improving our project! 💡

[pderrenger]

Thanks for the clear request—agreed this is a gap on iOS. We’ll add a public labelFontSize option in Plot.swift (nil = auto-scale) to mirror Python’s Annotator/results.plot behavior; happy to review a PR if you can open one. Until that lands, a quick local fix is to thread an optional font size through your renderer and use it when drawing labels, e.g. let font = UIFont.systemFont(ofSize: labelFontSize ?? autoFontSize(for: canvas)). For expected parity, see the Annotator font_size parameter and plot(font_size=…) in the Ultralytics Docs.