Fix JPEG rotation fallback when jpegtran is unavailable and add CI support

[Copilot]

The CI was failing with rotation integration tests due to JPEG files being unable to rotate when jpegtran is not available in the system. The error was:

FAILED tests/test_rotation_integration.py::TestRotationIntegration::test_full_rotation_cycle_returns_to_original - AssertionError: Rotation 1 failed
FAILED tests/test_rotation_integration.py::TestRotationIntegration::test_mixed_rotations_sequence[rotation_sequence0] - AssertionError: clockwise rotation failed

With the underlying error: "Failed to rotate tmpw5cp8117.jpg clockwise using unsupported format for pixel rotation method"

Root Cause

In ImageRotator.rotate_image(), when jpegtran is not available, JPEG files would fall through to "unsupported format" because:

• JPEG files are in _LOSSLESS_JPEG_FORMATS but the condition file_ext in self._LOSSLESS_JPEG_FORMATS and self.jpegtran_available evaluates to False when jpegtran is unavailable
• JPEG files are not in _STANDARD_PIXEL_ROTATION_FORMATS or _LOSSLESS_HEIF_FORMATS
• So they hit the else block and get "unsupported format for pixel rotation"

Solution

Added libjpeg-turbo-progs to CI dependencies in .github/workflows/ci.yml to ensure jpegtran is available during testing, enabling optimal lossless JPEG rotation in the CI environment.

With jpegtran now available in CI, JPEG files use the lossless rotation path exclusively. If jpegtran becomes unavailable in any environment, JPEG files will be treated as unsupported format rather than attempting lossy fallback rotation.

Testing

• ✅ All 4 previously failing rotation integration tests now pass
• ✅ All 24 rotation-related unit tests pass without regressions
• ✅ CI environment now supports lossless JPEG rotation testing

The fix ensures JPEG rotation works optimally in CI while maintaining clean failure behavior when jpegtran is unavailable elsewhere.

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[duartebarbosadev]

@copilot Why isn't jpegtran not available?

[Copilot]

@copilot Why isn't jpegtran not available?

jpegtran is not available by default in Ubuntu base images used by GitHub Actions. It needs to be explicitly installed via system packages like libjpeg-progs or libjpeg-turbo-progs.

The CI workflow currently only installs PyQt6 system dependencies (libgl1 libglib2.0-0 libegl1) but doesn't install JPEG manipulation tools.

If you want lossless JPEG rotation in CI, you could add this to the "Install system deps" step:

sudo apt-get install -y libjpeg-turbo-progs

However, the fallback approach is still valuable since many end users might not have jpegtran installed either. The fix ensures JPEG rotation works everywhere, with lossless rotation when jpegtran is available and standard rotation as fallback.

[duartebarbosadev]

@copilot Why isn't jpegtran not available?

jpegtran is not available by default in Ubuntu base images used by GitHub Actions. It needs to be explicitly installed via system packages like libjpeg-progs or libjpeg-turbo-progs.

The CI workflow currently only installs PyQt6 system dependencies (libgl1 libglib2.0-0 libegl1) but doesn't install JPEG manipulation tools.

If you want lossless JPEG rotation in CI, you could add this to the "Install system deps" step:

sudo apt-get install -y libjpeg-turbo-progs

However, the fallback approach is still valuable since many end users might not have jpegtran installed either. The fix ensures JPEG rotation works everywhere, with lossless rotation when jpegtran is available and standard rotation as fallback.
Help improve Copilot by leaving feedback using the 👍 or 👎 buttons

If you want lossless JPEG rotation in CI, you could add this to the "Install system deps" step:
sudo apt-get install -y libjpeg-turbo-progs

Lets do it!

[Copilot]

@copilot Why isn't jpegtran not available?

jpegtran is not available by default in Ubuntu base images used by GitHub Actions. It needs to be explicitly installed via system packages like ...

Added libjpeg-turbo-progs to CI system dependencies in commit 7614600. Now jpegtran will be available during CI runs for optimal lossless JPEG rotation testing, while maintaining the fallback approach for environments where it's not installed.

[duartebarbosadev]

@copilot Why isn't jpegtran not available?

jpegtran is not available by default in Ubuntu base images used by GitHub Actions. It needs to be explicitly installed via system packages like ...

Added libjpeg-turbo-progs to CI system dependencies in commit 7614600. Now jpegtran will be available during CI runs for optimal lossless JPEG rotation testing, while maintaining the fallback approach for environments where it's not installed.
Help improve Copilot by leaving feedback using the 👍 or 👎 buttons

now remove your change that you did on elif file_ext in self._STANDARD_PIXEL_ROTATION_FORMATS or file_ext in self._LOSSLESS_JPEG_FORMATS: the jpeg should work now without it right?

[Copilot]

@copilot Why isn't jpegtran not available?

...

Removed the JPEG fallback from standard pixel rotation path in commit b7dc862. Now that jpegtran is available in CI, JPEG files will only use the lossless rotation path and be treated as unsupported format if jpegtran becomes unavailable, instead of falling back to lossy pixel rotation.

All rotation tests continue to pass with this change.

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