[Enhancement] Reduce the image contrast

[vntraam]

As the picture shows below, Vcodex's image contrast is too high, that make it difficult to see image's detail.
I hope you can enhance this in the future release.

Image1
Vcodex

Other firmware

Image 2
Vcodex

Other firmware

[franssjz]

Thank you for the comparison photographs. They made the problem clear: CPR-vCodex was losing dark texture and shadow detail that remained visible in the other firmware.

I traced this to the fixed-threshold four-level Bayer conversion. Around the quarter-tone boundaries, the previous calculation could push an entire dark Bayer cell to black instead of preserving the source image’s average luminance.

I have replaced it with proportional ordered dithering across the complete 0–255 grayscale range. It preserves the four physical e-ink levels while distributing the fractional gray value across the Bayer cell, so dark detail should no longer be crushed. The change applies to the shared JPEG/PNG image path and does not add a framebuffer or recurring heap allocation.

New regression tests verify black/white endpoints, monotonic output and preserved average luminance, including the dark range shown in the report. Both firmware targets compile successfully. The correction is prepared for the next release, but I would still like an on-device comparison of the same page and refresh mode before declaring the visual result fully confirmed.

[vntraam]

I tried 1.6.0.32-cpr-vcodex but the picture's contrast is the same as before.

[franssjz]

Can you share the sample epub? Thanks!