Arm backend: Fix conversion from uint8 to fp32 for img_class application

[gggekov]

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18607

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 6 Cancelled Jobs, 4 Unrelated Failures

As of commit 6efa5e8 with merge base 07c5a54 ():

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• periodic / test-models-linux (buck2, mv3, portable, linux.2xlarge, 90) / linux-job (gh)
  ##[error]The operation was canceled.
• periodic / test-models-linux (buck2, mv3, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job (gh)
  ##[error]The operation was canceled.
• periodic / test-models-linux (cmake, mv3, portable, linux.2xlarge, 90) / linux-job (gh)
  ##[error]The operation was canceled.
• periodic / test-models-linux (cmake, mv3, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job (gh)
  ##[error]The operation was canceled.
• periodic / test-models-linux (cmake, vit, portable, linux.2xlarge, 90) / linux-job (gh)
  ##[error]The operation was canceled.
• periodic / test-models-linux (cmake, vit, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job (gh)
  ##[error]The operation was canceled.

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / test-huggingface-transformers-macos (olmo-1b|coreml_fp32_gpu|--quantize) / macos-job (gh) (detected as infra flaky with no log or failing log classifier)

BROKEN TRUNK - The following jobs failed but was present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• trunk / unittest-release / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[github-actions]

This PR needs a release notes: label

If your change should be included in the release notes (i.e. would users of this library care about this change?), please use a label starting with release notes:. This helps us keep track and include your important work in the next release notes.

To add a label, you can comment to pytorchbot, for example
@pytorchbot label "release notes: none"

For more information, see
https://github.com/pytorch/pytorch/wiki/PyTorch-AutoLabel-Bot#why-categorize-for-release-notes-and-how-does-it-work.

[Copilot]

Pull request overview

This PR updates the image preprocessing used by the Arm Ethos-U image classification runtime example so that RGB pixel values are converted from uint8 [0..255] into fp32 values in the model’s expected [-1..1] range.

Changes:

• Adjust input normalization from / 255.0 to / 127.5 - 1 to map [0..255] → [-1..1].
• Add explanatory comments describing the normalization rationale.
• Update the copyright header year range.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

There’s a missing space in the comment: 127.5(the middle of the range) reads as a typo. Please add a space after 127.5 for readability.

Suggested change

	# To pass from [0;255] to [-1;1], we divide by 127.5(the middle of the range)
	# To pass from [0;255] to [-1;1], we divide by 127.5 (the middle of the range)