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TAV: improved compression using some coefficient preprocessing

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minjaesong
2025-09-29 01:17:53 +09:00
parent 01278815c7
commit 66909537a0
5 changed files with 280 additions and 47 deletions
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terranmon.txt
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@@ -961,6 +961,23 @@ note: metadata packets must precede any non-metadata packets
uint8 Quantiser override Y (use 0 to disable overriding; shared with A channel)
uint8 Quantiser override Co (use 0 to disable overriding)
uint8 Quantiser override Cg (use 0 to disable overriding)
## Coefficient Storage Format (Significance Map Compression)
Starting with encoder version 2025-09-29, DWT coefficients are stored using
significance map compression for improved efficiency:
For each channel (Y, Co, Cg, optional A):
uint8 Significance Map[(coeff_count + 7) / 8] // 1 bit per coefficient
int16 Non-zero Values[variable length] // Only non-zero coefficients
The significance map uses 1 bit per coefficient position:
- Bit = 1: coefficient is non-zero, read value from Non-zero Values array
- Bit = 0: coefficient is zero
This format exploits the high sparsity of quantized DWT coefficients (typically
85-95% zeros) to achieve 15-20% compression improvement before Zstd compression.
## Legacy Format (for reference)
int16 Y channel DWT coefficients[width * height + 4]
int16 Co channel DWT coefficients[width * height + 4]
int16 Cg channel DWT coefficients[width * height + 4]