Module armor 

Armor mode: robust steganography resistant to JPEG recompression.

Armor mode trades undetectability for robustness by using:

• STDM (Spread Transform Dither Modulation) for embedding, which distributes each bit across multiple coefficients via spreading vectors
• Reed-Solomon error correction to recover from bit errors introduced by recompression
• Stability analysis to select coefficient positions that survive quality factor changes

Phase 2 adaptive robustness: When the message is small relative to the image capacity, the encoder automatically maximizes robustness by:

• Increasing RS parity (up to 240/255 symbols, from fixed 64/255)
• Repeating the RS-encoded bitstream r times across spare capacity
• Using soft majority voting with STDM log-likelihood ratios on decode
• Increasing the STDM delta for larger decision regions

Phase 2 activates transparently when r >= 3. Phase 1 images (r <= 1) are decoded using the original path for full backward compatibility.

The pipeline: encrypt -> frame -> RS encode -> [repeat r×] -> STDM embed.

Modules

capacity

Armor mode capacity estimation.

dft_payload

DFT ring payload: a resize-robust second payload layer.

ecc

Reed-Solomon error correction over GF(2^8).

embedding

STDM (Spread Transform Dither Modulation) embedding and extraction.

fft2d

Deterministic 2D FFT/IFFT using only WASM-intrinsic f64 operations.

fortress

Fortress sub-mode: BA-QIM embedding in DC block averages.

pipeline

Armor encode/decode pipeline.

repetition

Repetition coding with soft majority voting.

resample

Bilinear resampling for undoing geometric transforms.

selection

Frequency-based coefficient selection for Armor embedding.

spreading

Spreading vector generation for STDM embedding.

template

DFT template generation, embedding, detection, and transform estimation.