wai-rs: validate jpegai_icci against the reference decoder (ground truth, 2.4e-07) #26
2026-07-18
wai-rs: validate jpegai_icci against the reference decoder (ground truth, 2.4e-07)
Adds a calibration test driving the merged IcciPath with ground truth captured from the
ISO reference decoder running on the real test256.bin: the reference's own
process_dwt444_2 outputs (48-ch network input + the plane's 16 subbands), the selected
model's weights, and the reference's process_comp output.
Result: max|Δ| = 2.4e-07 (float epsilon). This is the first validation of the eICCI
implementation against real chain data rather than against my reading of the source, and
it confirms the whole plane path: conv_first + BN-fold + ReLU -> residual blocks (rect
[1,3]/[3,1] kernels, folded BN, scaled residual) -> conv_last -> out*scale + subbands
-> two-level inverse Haar.
Two things this pinned down, both of which had produced false confirmations earlier:
- the decoder never calls the model's `forward` (which is what post_filters/model_*.onnx
exports); it calls process_dwt444_2 once and process_comp per plane, so the exported
ONNX is the wrong artifact to drive. Weights must come from the reference state_dict,
whose tensors are unfolded and complete (the ONNX initializers are pre-folded and
lack BNY, scaleU/scaleV and the per-block scale).
- model_selection is 1-based (0 = plane not filtered), so [6,3,3] selects active[5] and
active[2] — confirmed by hooking the reference, not by re-reading the code.
Separately verified in the same run (numpy, same ground truth): the joint-UV path — one
shared trunk feeding conv_last_u/conv_last_v with distinct scaleU/scaleV — reproduces
U at 1.62e-07 and V at 1.65e-07, and the two-level Haar DWT reproduces the reference's
Y16/U16/V16 and the 48-channel concat exactly (0.0).
Co-Authored-By: Claude Opus 4.8 <[email protected]>