Add OKLab color space support

[adamjtaylor]

Summary

• Adds OKLab color space as a new colormap option alongside existing LAB and RGB
• OKLab provides superior perceptual uniformity where Euclidean distance directly corresponds to perceived color difference (no need for complex CIEDE2000 calculations)
• Addresses known CIELAB non-uniformities, particularly in the blue-purple range

Changes

• ucie.py: Added generate_oklab_grid(), oklab_to_rgb_vectorized(), updated get_target_hull() and optimize_embedding() to support OKLAB target
• core.py: Added assign_colours_oklab() function, added OKLAB to CLI choices and default 3D colormap list
• init.py: Exported assign_colours_oklab
• tests: Added comprehensive tests for all new OKLab functionality

Usage

# Use OKLab colormap
paint_miniature input.tiff output.png --colormap OKLAB

# Generate all 3D colormaps (now includes OKLAB)
paint_miniature input.tiff output.png --colormap ALL --n_components 3

Test plan

• All existing tests pass
• New OKLab tests pass (test_assign_colours_oklab, test_generate_oklab_grid, test_oklab_to_rgb_vectorized, test_optimize_embedding_oklab, test_get_target_hull_oklab)
• Visual comparison of LAB vs OKLAB output on sample images

🤖 Generated with Claude Code

[claude]

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Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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