f96b6ab29c
## Summary * **What is the goal of this PR?** Replace simple threshold-based grayscale quantization with ordered dithering using a 4x4 Bayer matrix. This eliminates color banding artifacts and produces smoother gradients on e-ink display. * **What changes are included?** - Add 4x4 Bayer dithering matrix for 16-level threshold patterns - Modify `grayscaleTo2Bit()` function to accept pixel coordinates and apply position-based dithering - Replace simple `grayscale >> 6` threshold with ordered dithering algorithm that produces smoother gradients ## Additional Context * Bayer matrix approach: The 4x4 Bayer matrix creates a repeating pattern that distributes quantization error spatially, effectively simulating 16 levels of gray using only 4 actual color levels (black, dark gray, light gray, white). * Cache invalidation: Existing cached `cover.bmp` files will need to be deleted to see the improved rendering, as the converter only runs when the cache is missing.
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